MRI based on iron oxide nanoparticles contrast agents: effect of oxidation state and architecture

Abstract

Iron oxide nanoparticles (IONPs) extensively employed beyond regenerative medicines to imaging disciplines because of their great constituents for magneto-responsive nano-systems. The unique superparamagnetic behavior makes IONPs very suitable for hyperthermia and imaging applications. From the last decade, versatile functionalization with surface capabilities, efficient contrast properties and biocompatibilities make IONPs an essential imaging contrast agent for magnetic resonance imaging (MRI). IONPs have shown signals for both longitudinal relaxation and transverse relaxation; therefore, negative contrast as well as dual contrast can be used for imaging in MRI. In the current review, we have focused on different oxidation state of iron oxides, i.e., magnetite, maghemite and hematite for their T1 and T2 contrast enhancement properties. We have also discussed different factors (synthesis protocols, biocompatibility, toxicity, architecture, etc.) that can affect the contrast properties of the IONPs.
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Full text

REVIEW
MRI based on iron oxide nanoparticles contrast agents: effect
of oxidation state and architecture
Ya s i r J a v e d &Kanwal Akhtar &Hafeez Anwar &
Ya s i r J a m i l
Received: 4 July 2017 /Accepted: 9 October 2017
#Springer Science+Business Media B.V. 2017
Abstract Iron oxide nanoparticles (IONPs) extensively
employed beyond regenerative medicines to imaging
disciplines because of their great constituents for
magneto-responsive nano-systems. The unique
superparamagnetic behavior makes IONPs very suitable
for hyperthermia and imaging applications. From the
last decade, versatile functionalization with surface
capabilities, efficient contrast properties and biocom-
patibilities make IONPs an essential imaging contrast
agent for magnetic resonance imaging (MRI). IONPs
have shown signals for both longitudinal relaxation
and transverse relaxation; therefore, negative contrast
as well as dual contrast can be used for imaging in
MRI. In the current review,wehavefocusedon
different oxidation state of iron oxides, i.e., magnetite,
maghemite and hematite for their T
1
and T
2
contrast
enhancement properties. We have also discussed different
factors (synthesis protocols, biocompatibility, toxicity,
architecture, etc.) that can affect the contrast properties
of the IONPs.
Keywords Iron oxide nanoparticles .Magnetic
resonance imaging .Contrast agents .Longitudinal
relaxation (T
1
).Transverse relaxation (T
2
).
Functionalization .Biocompatibility.Biomedical
applications
Introduction
Nanoparticles (NPs) have revolutionized the medical
field through attractive change toward diagnostic,
theranostic and therapeutic tools because of their
comparable sizes to biomolecules. However, due to
toxicity issues, only few selective designed NPs have
reached clinical and preclinical trials. Among all
these NPs, IONPs hold the great potential for success
in contrast imaging techniques because of reduced
toxicity, biodegradability and rapid response to the
magnetic field. Additionally, their bio-distributed
quantitative evaluation is also extensively investigat-
ed through in vivo and in vitro trails (Dürr et al.
2013; Tombácz et al. 2015). In living organisms, iron
is most important transition metal that is indispensable
for biological processes and can be incorporated in
human body with natural metabolic pathways (Ling
and Hyeon 2013;Mazueletal.2016).
Owing to their physiochemical properties, IONPs
have been benefited for both in vitro applications such
as magnetic transfection and magnetic detection/sensing
and in vivo applications such as tissue engineering,
targeted drug delivery, molecular imaging and magnetic
particle imaging (Chatterjee and Sarkar 2013;Wuetal.
2013; Xu and Sun 2013). Ferrite colloids including
maghemite (γ-Fe
2
O
3
) and magnetite (Fe
3
O
4
) are con-
sidered as primary representative of superparamagnetic
IONPs in MRI techniques (Reddy et al. 2012;Bashir
et al. 2014;Riazetal.2014). High-quality conventional
IONPs synthesis has been reported by using top down
approach including physical vapor deposition techniques
JNanopartRes (2017) 19:366
https://doi.org/10.1007/s11051-017-4045-x
Y. Javed (*):K. Akhtar :H. Anwar :Y. Jamil
Department of Physics, University of Agriculture, University
Main Rd, Faisalabad 38000, Pakistan
e-mail: myasi60@hotmail.com

(Liu and Chi 2016) and bottom up approaches such as
sol-gel (Arshad et al. 2016;Bhosaleetal.2016; Masthoff
et al. 2016;Zengetal.2016), assisted sol gel (Masthoff
et al. 2016), hydrothermal reactions (Bhavani et al. 2016),
electrospinning (Leonardi et al. 2016; Patel and Hota
2016), co-precipitation (Primc et al. 2016;Soodetal.
2016), thermal decomposition (Glasgow et al. 2016;
Wetterskog et al. 2016) and non-aqueous sol-gel
(Masthoff et al. 2016). Doping of iron oxide with other
metal alloys and magnetically susceptible elements are
also under investigation for biomedical applications
(Ling and Hyeon 2013).
During the last decade, combining nanotechnology
with molecular imaging methods generates new
noninvasive diagnosis strategies (Chen et al. 2011).
Imaging techniques facilitate in visualization of
structural and functional analysis of biological processes
which leads to open up new pathways for researcher to
recognize and diagnose diseases at early stages
(Padmanabhan et al. 2016). Molecular imaging can be
classified into optical fluorescence, photo-acoustic
tomography, single photon emission tomography,
ultrasound, MRI, positron emission tomography,
optical bioluminescence and magnetic resonance
spectroscopy (Bulte and Kraitchman 2004; Hao et al.
2010). MRI provides enhanced soft tissue contrast with
fantabulous anatomical detail. MRI results can be fur-
ther improved by acquisition techniques with the use of
different imaging agents including superparamagnetic
multi-functional IONPs (Harisinghani et al. 2003).
Superparamagnetic nature of IONPs can be exploited
in MRI that uses strong magnetic field for diagnostic
purposes of different pathological changes and lesion in
body. Combination of radiofrequency pulse with mag-
netic field is used in MRI for imaging different body
organs that contain IONPs. IONPs not only meliorate
contrast of image but also ensure targeted imaging of
particular organs in geriatrics and pediatric patients
(Mulens et al. 2013; Umair et al. 2016).
According to relaxation process, MRI images are
classified into longitudinal relaxation time weighted
images (T
1
contrast) and transverse relaxation time
weighted images (T
2
contrast). Contrast agents in MRI
are used for better visualization of internal body struc-
ture (Bulte and Kraitchman 2004;JenningsandLong
2009; Na et al. 2009; Hao et al. 2010). Small-sized
IONPswithdiameter(<4nm)arepreferredasT
1
contrast agents while nanoparticles having diameter
greater than 4 nm that are used as T
2
contrast agents
(Lawaczeck et al. 2004;Kimetal.2011;DeMontferrand
et al. 2013). IONPs-based MR contrast agents provide
high spatial resolution with excellent visualization to
human body’s fine structure (Kim et al. 2009). These
IONPs-based MR contrast agents provide clear images
by maintaining an influence on both longitudinal relaxa-
tion time and transverse relaxation time on all nearby
tissues for diagnosis. Superparamagnetic IONPs are also
widely used for ultrasensitive negative contrast agents for
early-stage cancer detection because of strong T
2
short-
ening effect (Chen et al. 2009;Neamnarketal.2009;Liu
et al. 2011).
This review summarizes the discussion on IONPs for
MRI contrast agents depending on different parameters
such as oxidation state, composition, assembly and
doping.
Preparation methods for IONPs
Synthesis of magnetic NPs with customized shape and
size is one of the most technologically and scientifically
challenging task. Different physical and chemical
approaches are being used for this purpose. The
examples of physical methods are sputtering
(Sheng-Nan et al. 2014; Couture et al. 2017;Sood
et al. 2017), evaporation, electron beam lithography
and gas phase deposition while chemical methods are
sol gel (Cui et al. 2013; Di Carlo et al. 2014;Ba-Abbad
et al. 2017), co-precipitation (Kandpal et al. 2014),
thermal decomposition (Hufschmid et al. 2015), polyol
(Hachani et al. 2016a) and hydrothermal and reflex
method (Gupta and Curtis 2004; Gupta and Wells
2004). Electron beam lithography and gas phase depo-
sition suffer with size control inabilities in the
nanometric range. Chemical approaches are easier, sim-
pler and more manageable with respect to size, shape
and composition in comparison to physical ap-
proaches (Gupta and Gupta 2005).
Co-precipitation Co-precipitation is considered the
most conventional method that consist of mixed
ferrous and ferric ions at room temperature in basic
solution with 1:2 molar ratio. When pH of solution
is less than 11, nucleation of iron ions is much
easier while growth mechanism is faster at pH
higher than 11. After Massart work on Fe
3
O
4
NPs
synthesis, co-precipitation method start reported on
large scale with extraordinary advantages involving
366 Page 2 of 25 J Nanopart Res (2017) 19:366

gram scale facility and production (Wu et al.
2015a). Many co-precipitation modified methods
have been established and reported as well. Wu et al.
synthesized powder of magnetic Fe
3
O
4
by
ultrasonic-assisted co-precipitation method with aver-
age size ~ 15 nm (Wei et al. 2007;Wuetal.2011;
Pereira et al. 2012). Co-precipitation method involve
fast formation of NPs that is why particle size and
distribution is hardly controllable.
Thermal decomposition Thermal decomposition is used
to avoid such limitations. Thermal decomposition is
used to synthesize monodisperse and highly crystalline
NPs (Sun and Zeng 2002; Woo et al. 2004;Lietal.
2008). During NPs synthesis, thermal decomposition
generally offers two routes for good control over
nucleation and growth mechanism. One route involves
direct injection of organometallic compounds in hot sur-
factant solution that results in instantaneous formation of
nuclei. Another route involve control heating of these
compounds in surfactant solution for nuclei formation
(Hyeon et al. 2001). At high temperature, particles start
growing after nucleation occurred. NPs growth can be
stopped through quick decrease of reaction temperature.
NPs size can be controlled with variations in solvents, Fe/
oleic acid ratio, and precursor concentrations (Park et al.
2005;Rocaetal.2006; Baaziz et al. 2014). Single core
iron oxide based nanocubes with 20 to 160 nm have been
synthesized in benzyl ether and oleic acid with iron
acetylacetonate (Kim et al. 2008). Iron pentacarbonyl
and iron oleate were used as alternative precursors
(Roca et al. 2006;Rocaetal.2007).
Micro-emulsion Micro-emulsion is a widely used
synthesis technique along with better control on size
of NPs. Particle size is controlled strictly with water
droplet size. Micro-emulsion is defined as stabilized
isotropic dispersion of two mutually saturated immiscible
liquids. Stabilized microdomains of one or both liquids
are obtained through interfacial film. In aqueous phase,
water in oil micro-emulsion, microdroplets (1–
50 nm) are formed by monolayers that consist of
surfactant molecules (Lawrence and Rees 2000;
Bagwe et al. 2001). With incorporation of soluble
metal salt in micro-emulsion, aqueous phase will
result in residing oil surrounded microdroplets. These
microdroplets will constantly coalesce, collide and
break again. When reactants (A and B) are dissolved
and mixed separately in water in oil micro-emulsions,
AB precipitate will form. Growth mechanisms in
micro-emulsion result in inter-droplet exchange and
aggregation of nuclei. It involves preparation of two
separate inverse micro-emulsions with use of some
suitable surfactants (Chin and Yaacob 2007;Yen
et al. 2013). First micro-emulsion solution consists
of FeCl
3
and FeSO
4
while second micro-emulsion is
a base that can be either NH
4
OH or NaOH. After
stirring both emulsions, second micro-emulsion is
drop-wise added to first micro-emulsion. Micro-
emulsion solutions are placed in ultrasonic bath so
that reactants mixed well with the collision of water
droplets, as a result NPs will produce (Santra et al.
2001;TartajandSerna2002).
Sol gel method This is a progressively used synthesis
technique for metal oxides and need low temperature to
modify precursors. This method provides many advan-
tages over other preparation techniques such as low cost,
good homogeneity and high purity (Jitianu et al. 2006).
Metalorganic precursor was used for magnetite prepara-
tion in recent past. In order to achieve more uniformity
along with high crystallinity, different synthesis tech-
niques can be used but they usually involve complicated
synthetic steps and toxic reagents (Chen and He 2001;
Trewyn et al. 2007;Jagadaleetal.2008). Sol gel method
involve inorganic species with successive condensation
and hydrolysis reactions. In the start of chemical reac-
tion, with release of alcohol molecule, reactive group is
released from water molecule. NPs are formed with the
poly-addition and poly-condensation reactions. Kinetics
of condensation and hydrolysis is greatly influenced by
temperature, solvent type/nature, pH and precursor con-
centration (Clapsaddle et al. 2003;Naginenietal.2005;
Xu et al. 2007). Dispersion phase called sol can be
prepared from organic or inorganic precursors. Dis-
persed phase of suspension is small enough (~1–
1000 nm) that result in negligible gravitational and
short-range forces due to dominant interactions.
Brownian motion is driven due to dispersion phase that
produces small inertia. Colloidal suspension in liquid of
solid particles referred as gel (Laurent et al. 2010;Jain
et al. 2012; Matijevic and Borkovec 2012).
Polyol Process Polyol method is modification of
thermal decomposition method because here solvent used
for reactions is polyethylene glycol or its derivatives.
In a stoichiometric polyol mixture, there is alkaline
hydrolysis of Fe
3+
and Fe
2+
. In metallic precursor,
JNanopartRes (2017) 19:366 Page 3 of 25 366

liquid polyol plays the role of solvent. Polyols prevent
interparticle agglomeration with greater control on
shape and size of prepared materials. Structure and size
of synthesized particles are greatly influenced with
temperature variation, choice of solvent, nature of
precursor and duration for which reaction influenced
(Cheng et al. 2011;Hachanietal.2016b). In this
method, hydrophilic polyol ligand coatings on the
surfaces of NPs allow them for easy dispersion in
many polar solvents. High reaction temperature dur-
ing the synthesis provides greater control on size
along with higher crystallinity and magnetization.
Polyol synthesis provides narrower particles size in
comparison to organometallic compounds prepared
through thermal decomposition (Fornara et al. 2008;
Laurentetal.2008; Gutiérrez et al. 2015).
Pyrolytic method Physical pyrolytic methods are
usually not considered economical. But it is widely
used due to fast formation of magnetic NPs with
uniform sizes by controlling many experimental
parameters including nature of precursor, flow rate
of reagent in pyrolysis zone and laser power (Tartaj
et al. 2004; Bomatí-Miguel et al. 2005). One of the
major advantage of this technique is its flexibility along
with great control on crystallinity, size and chemical
compositions. This method also involves synthesis of
silica-coated maghemite NPs. Main restrictions usually
faced during synthesis is requirements of specific laser
resonance installation and availability of reagents
(David et al. 2004;Janaetal.2004; Basak et al. 2007).
Hydrothermal and reflex method Hydrothermal
methods is developed for synthesis of
polydispersed single-crystal IONPs. In this method,
decomposition of respective organometallic precur-
sors take place in the presence of suitable surfac-
tants (long-chain carbons having amines and
carboxylic functions) (Sun et al. 2004;Tangand
Chen 2007;Tavakolietal.2007;XuandTeja
2008). These aqueous hydrothermal reactions can
be carried under pressure and temperature ranges of
14 bars and 200 °C respectively. Water not only
plays the role of solvent but it accelerates the
hydrolysis reactions by acing as reagents. These methods
can also be carried out with organic solvents. Due to
stabilizing agents, non-aggregated crystals are formed
with high control over density, purity, and size (Mao
et al. 2006; Simeonidis et al. 2007; Takami et al. 2007).
Presence of different solvents in the preparation
methods played very important towards size, size distri-
bution, primary coating, etc. These coatings require to
replace by biocompatible polymer using some ligand
exchange method. Suspension phase change of NPs is
also necessary to make NPs colloids suitable for in vivo
trails. Therefore, it is necessary to follow appropriate
synthesis protocol so that minimum steps required for
making NPs suspension are acceptable for human
systems.
Bio-compatibility and toxicity of IONPs
Most important in vivo applications of IONPs include
non-invasive monitoring of immune or stem cell
migration after implantation. Cells are grown isolated
so IONPs can reach at specific targets in sufficient num-
bers, after that labelling is done with IONPs for MRI
detection purposes. MRI is considered as inherently
insensitive technique that provides enhanced cell moni-
toring abilities with high contrast generation for longer
duration by fulfilling the requirement of cell remain
loaded with large amount of IONPs (Díaz et al. 2008;
Jain et al. 2012). IONPs are extensively explored as
contrast agent in MRI for pharmacokinetics and tumor
localization (Li et al. 2013). IONPs have detrimental
effects such as inflammation, genotoxicity, oxidative
stress and intracellular interference signaling (Li and
Chen 2011; Bondarenko et al. 2013). Several mecha-
nisms of NPs can cause toxicity in body, but in vivo and
intracellular toxicities of NPs arise from excessive gen-
eration of reactive oxygen species (ROS). Dislocations
of IONPs induces oxidative stress in the body due to
catalysis of ROS formation and generation of OH
−
and
OOH
−
radicals vie Fenton reaction from H
2
O
2
.ROS
production can be minimized with use of inert
nanomaterials. Physiologically, ROS is necessary but
considered potentially destructive. Signal transduction,
gene expression, protein redox regulation and prolifera-
tive responses greatly affected with ROS level (Nel et al.
2006; Xia et al. 2006; Unfried et al. 2007;Mølleretal.
2010). Oxidative stress is produced due to high ROS
level; consequently, it can damage several cells by
disrupting DNA, peroxidizing lipids, protein alternation,
interfering gene transcription and signaling functions.
Cell signaling is greatly affected by oxidative stress
induced by NPs in three stages. Transcription of defense
genes are enhanced at low oxidative stress, inflammation
366 Page 4 of 25 J Nanopart Res (2017) 19:366

signaling is activated at high oxidative stress while
necrosis and apoptotic pathways are activated at very
high oxidative stress level (Bermudez et al. 2004;
Oberdörster et al. 2005; Sayes et al. 2005; Dalle-
Donne et al. 2007; Halliwell and Gutteridge 2015)
(Fig. 2). In cells, change in signaling pathways of
NPs results in causing carcinogenic effects. Accumu-
lationofNPscanresultinbreaking single stands
while double stands break due to induced oxidative
stresses that considered as lethal oxidative damage to
DNA. Excess ROS can cause mitochondrial damage
that leads toward several syndromes such as ataxia,
mitochondrial encephalomyopathy, retinitis pigmentosa
and neurogenic muscle weakness (Oberdörster 2004;
Warheitetal.2004;Lietal.2008; Petersen and
Nelson 2010).
These toxicity problems can be resolved by coating
nano-scaled inert materials organic/inorganic on iron
oxide surface (Fig. 1). Nanomaterial’s toxicity is dose
dependent in association with surface engineering and
size (Yang et al. 2011). In case of IONPs, it highly
relies on dosage, surface chemistry, solubility, structural
properties, biodegradability, routes of administration,
bio-distribution and pharmacokinetics (Markides et al.
2012; Gautam and van Veggel 2013). NPs toxicity can
be evaluated by toxicity assays such as lactate dehydro-
genase (LDH), mitochondrial metabolism (MTT) and
calcein acetoxymethyl ester assays. Originally, these
tests were built up for drug-associated toxicity effects
that are not well established for addressing mediated
NPstoxicity.MTTassayshavebeenusedtoevaluate
high level ROS (distributed in cells with natural
equilibrium redox state) and free amine groups on the
surface of NPs (Sohn et al. 2008; Monteiro-Riviere et al.
2009) (Fig. 2). Protein bindings influenced lactate
dehydrogenase in NPs that results its release in the
extracellular medium. All the above tests are used
generally for determination of cytotoxicity in single
parameter (cellular esterase, mitochondrial activity
and plasma membrane permeability) and is highly
recommended for multiple assays (Hoshino et al.
2004; Soenen et al. 2009). These can be further used
(even when effects appeared unlikely) for investiga-
tion of broad spectrum of NPs with possible potential
interferences with cellular components (Díaz et al.
2008; Soenen et al. 2009).
To control nanotoxicity, most important and relevant
parameter is surface coating of magnetic IONPS
(Pisanic et al. 2007). Homogenous surface coating is
required to obtain stabilized particles, prevent dissolu-
tion, avoid agglomeration and limit release of toxic ion.
Polyethylene glycol (PEG) is extensively used polymer
coating for IONPs. PEG induces no toxicity and its
circulation life time is based on its molecular
weight. PEG also reduces harmful interactions with
the biological system (Lartigue et al. 2012). Dextran
is a branched polysaccharide used for coating IONPs
and it was the part of initially approved IONPs with
Inorganic Shell
Iron Oxide
Contrast agent
Targeting Antibody
Fe3O4
γ-Fe2O3
α-Fe2O3
Au
SiO2
Other
Materials
PEG
DEXTRAN
PVP,
Citrate, ….
IgG
IgM
Polymer layer
Nanoparticle’s
Architecture
Spherical,
Cubes, triangles
Nanoflowers,
Dimers, …
Alloys, Core-
Shell …
Fig. 1 Schematic diagram of magnetic iron oxide NPs along with its different aspects for in-vivo applications
JNanopartRes (2017) 19:366 Page 5 of 25 366

the name of Feridex IV®. Amphiphilic is a micelle-like
coating that has a hydrophobic layer and hydrophilic
head (Fig. 3). Some toxic effects have been probed for
this polymer but due to better cover rate, it stays for a
longer time in the body. Steric hindrance of proper coat-
ings prevents accumulation and cellular uptake of NPs
while it facilitates endocytosis. Through coatings,
modified surface composition/charge greatly impact the
intracellular distribution and ROS production that causes
toxicity. Many coatings are degradable or labile that may
shed after their exposure to biological media. This results
in rendering nontoxic material into hazardous one.
Several studies have reported severe immunological
and inflammatory responses that occurred after a
certain duration of time (Kato et al. 2003; Otsuka
et al. 2003;Kirchneretal.2005;Morrisetal.2007).
Coatings are avoided for some NPs included
quantum dots, because in such cases, metallic coatings
are hydrophobic and the core of such materials are
consisted of heavy metals that causes toxicity. In such
cases, secondary coatings are done for increased water
stability/durability and to prevent the effect of ion
leaching (Chen and Gerion 2004;Zhaoetal.2010b;
Sharifi et al. 2012). However, surface coating itself has
certain limitations that can affect the efficacy of the NPs.
For example, surface coating greatly effects smooth
cellular uptake, biocompatibility and plasma half-life.
Above a specified concentration level, uncoated NPs
usually exhibit cytotoxicity (Liu et al. 2013; Mou et al.
2015; Hajba and Guttman 2016)(Fig.4).
Oxidave Stress
Iron Oxid e
Nanoparcles
Fenton Reacon
Generaon of
OH-and OOH-
Inert nano-material
Low Moderate High
Transcription of
defense genes Expression of
Inflammatory
pathways
Apoptosis and
necrosis
Fig. 2 Schematic representing ROS generation and different pos-
sible stages due to ROS
Fig. 3 Diagrammatic representation of polymer coating on the IONPs: different types of coating are available and can be used according to
different requirements or grafted during the synthesis method
366 Page 6 of 25 J Nanopart Res (2017) 19:366

Another important factor that needed more attention
is the interaction of NPs with various types of proteins
when injected in the body. These proteins can form a
layer around the NPs or even can replace the coated
layer with protein which results in the change in
complete identity of the NPs in the body and conse-
quently can affect the efficiency of nano-systems.
These protein interaction or binding to the NPs surface
is called protein corona and divided into soft and hard
corona. In soft corona, biomolecules (proteins) dynam-
ically show rapid exchange predominantly between par-
ticles and medium, while in the case of hard corona,
particle surface have high infinity with long residential
time for biomolecules (Aggarwal et al. 2009;Monopoli
et al. 2011). Hard corona makes identification and
isolation easier. Hard corona proteins make direct
interaction with NPs surface while soft corona show
indirect interaction according to Simberg model (they
interact through weak protein-protein interaction
with hard corona). Absorbed corona layer does not
mask completely the surfaces of NPs (Gessner et al.
2002; Lynch 2007). Superparamagnetic IONPs incuba-
tion in plasma result in protein corona formation but did
not significantly changes the lifetime for circulation as
reported in dextran-coated superparamagnetic IONPs
(Simberg et al. 2009; Walkey and Chan 2012). Protein
corona thickness is greatly affected by different factors
such as surface properties, particle size and protein
concentrations. Most of the proteins are present with
hydrodynamic diameter with 3–15 nm thickness. Co-
ronas of such NPs are thick enough which show that
they are usually consist of multiple layers that signifi-
cantly control environment interactions (Colvin 2003;
Cedervall et al. 2007; Tenzer et al. 2013).
NPs become coated with proteins as soon as they
enter in biological fluid that results in transmitting many
changes on biological effects due to alteration in protein
configuration, perturbed functioning, novel epitopes
exposure and arising of avidity effects due to spatial
close repetition by the same protein (Kasche et al.
DNA damage Cell membrane
leakage
Chromosome
Condensation Apoptotic
bodies
Fig. 4 Pictorial summary of potential toxicity of iron oxide NPs
JNanopartRes (2017) 19:366 Page 7 of 25 366

2003; Souto and Müller 2010). To determine the
different biological effects associated with different
receptors, rate of bindings and dissociation of proteins
play the critical role (Nyström and Fadeel 2012).
Protein-protein complexes lifetime typically vary from
microseconds to weeks while protein-ligands lifetime
varies from microseconds to days (Gref et al. 2000;
Gessner et al. 2003).
To understand the nature of NPs surface, complete
knowledge of stoichiometries, kinetic bindings,
equilibrium affinities, association and dissociation
rates of protein is important. A protein with more
specificity and high affinity for particular type of
receptor plays a key role. Many essential methods
have been developed to identify minor and major proteins
associated with NPs as well as binding competition
present between protein (especially major serum proteins,
fibrinogen and IgG) under thermodynamic and kinetic
control system (Sun et al. 2003; Cedervall et al. 2007).
Central problem is separation of free protein bounded to
NPs. Albumen is the most abundant protein that is almost
observed always on NPs surface and possibly retrieved if
it is present with low affinity. Other protein binds on
NPs surface on the following configuration assays:
alpha-1-antitrypsin, apolipoproteins and immuno-
globulins. Other than these proteins, there is very
low binding chances. Walkey et al. confirmed in their
studies that typical plasma protein usually consist
upon 2–6 high abundant proteins while many others
will absorbed with very low abundance (Labarre
et al. 2005;Salvador-Moralesetal.2006).
Surface charge on NPs is one of the most promising
influencing factors in protein interaction. NPs with
positive charge can adsorb protein having isoelectric
points < 5.5 (e.g. albumin) while NPs with negative
charge greatly enhances adsorption of protein with
isoelectric points > 5.5 (e.g. IgG). Surface charges in
some cases results in denaturing of adsorbed proteins
as reported in the study of Lynch (Gessner et al. 2002
; Lynch and Dawson 2008; Aggarwal et al. 2009).
Second major factor that decrease the protein
corona formation is surface re-functionalization and
pre-coatings. Aggarwal et al. reported a detailed
summary on efficacy of coatings, e.g. poloxamer,
polysorbate, PEG, polyoxyethylene and poloxamine,
on adsorbed quantity of plasma protein, and their
phagocytic uptake along with distribution. Major
changes in respective tissues/organs due to PEG-
coated NPs with selective bio-distribution along with
clearance confirmed that immune-adapted proteins
(fibrinogen and IgG) bind more than in comparison
to albumin irrespective of PEG chain length
(Lindman et al. 2007;Aggarwaletal.2009).
Third major factor is size of NPs. Protein binding
affinities are different due to surface curvature/flat
surfaces for different NPs. On flat surfaces, protein
adsorption data for NPs should not be extrapolated.
NPs having different sizes show different protein
corona formation (Monopoli et al. 2011). Composi-
tional and organizational changes are significant for
corona proteins. Less protein-protein interactions
were reported for high curved surfaces by Lynch
which confirmed fewer changes (Lynch and
Dawson 2008). For dextran-coated NPs, IgM-
dependent activation is more efficient on optimal size
range of approximately 250 nm, while large NPs do
not attract and activate much IgM. Dobrovolskaia
et al. reported that NPs with size range 30–50 nm
adsorbed more protein (Dobrovolskaia et al. 2009).
The term Bbiocompatibility^usually referred for
IONPs as necessary asset in the biological context.
When acute cytotoxic effects are not present, IONPs
are considered biocompatible. Biocompatibility can be
defined as when particle is taken by cells having no
effects on cell homeostasis (which means before and
after labelling, no difference in cellular parameters have
been observed) (Díaz et al. 2008; Soenen and De
Cuyper 2009; Soenen et al. 2011).
Before any cytotoxicity evaluation, an important
step is to thoroughly characterize IONPs with the
interpretation of all the obtained cytotoxicity data.
The following points should be checked carefully:
hydrodynamic radius, core size of particles (with
electron microscopy), contaminations present, purity
of particles, zeta potential (electrophoretic mobility
measurements), type and characteristic of stabilizing
coatings. Complete evaluation of IONPs potential
aggregation in serum and physiological saline con-
taining cell medium. There needs to be a standardi-
zation process that gives cytotoxic profile contain
complete assessment of those labelled IONPs effi-
ciency in comparison to already marketed IONPs
(Rivera Gil et al. 2010; Duzgunes and Düzgüneş
2012; Grabinski et al. 2014).
For MRI studies, IONPs are internalized in labeled
cells that are slightly adherent to plasma membranes.
When cells are transferred and put under some shear
stress, IONPs start dissolution. To study cytotoxic
366 Page 8 of 25 J Nanopart Res (2017) 19:366

effects of these internalized IONPs, internalization of
these NPs must be verified. For verification of these
intracellular localization of IONPs of labelled cells,
transmission electron microscopy (TEM) is preferably
used. NPs that usually reside in lysosomes or endosomal
structures (that are intracellular compartments of cell) can
be detected (Schäfer et al. 2007; Mailänder et al. 2008).
Cell viability assays are one of the most important
cytotoxicity assays and can be separated into many
subgroups depending on their detection modes; for
instance, cell metabolism (Alamar Blue1), cell membrane
integrity (e.g. lactate dehydrogenase assay (LDH),
Trypan blue exclusion assay), nucleic acid staining
(Propidium iodide staining) and lysosomal membrane
integrity (Neutral red). These different assays are used
for determining cellular toxicity aspects (Monteiro-
Riviere et al. 2009; Soenen and De Cuyper 2009).
For Fe
3+
ions, cytotoxic effects usually begins at
concentration of 4 mM, yet negative contrast signifi-
cantly observed 20-fold lower in comparative to toxic
level (Brunner et al. 2006; Pisanic et al. 2007). Dextran-
coated superparamagnetic IONPs is an illustrative and
powerful platform for multifunctional imaging agents.
These structures with their derivatives provide support
for diagnostic imaging through positron emission
tomography, MRI and optical fluorescence. Toxicity
and pharmacokinetic studies confirm that certain NPs
are sufficiently biodegradable and nontoxic with
FDA approval (Tassa et al. 2011).
Silica coatings on IONPs grown by stober method
results in excellent imaging performance with varying
concentration of iron for measurement of T
2
-weighted
signals and relaxivity (Yazdani et al. 2016). Non-
disperse and discrete mesoporous silica NPs that
consist upon mesoporous silica shell along with sin-
gle magnetite (Fe
3
O
4
) nanocrystal core are used as
imaging agents in fluorescence and MRI (Kim et al.
2008). To reduce toxicity of IONPS, different coatings
such as fluorophore-tagged superparamagnetic IONPs, L-
dopa-coated manganese oxide NPs were developed and
used in contrast imaging (Wang et al. 2015; Yalcin et al.
2015; Eghbali et al. 2016; McDonagh et al. 2016).
To assess safety of IONPs more efficiently, many
changes can be made with all possible effects of cell
labelling. Standardization protocols are needed for use
of certain materials (dextran-coated particles) along with
cell labelling. Iron oxide formulations are efficiently
compared to the systems having single cell model. More
in-depth analysis with more cautions of cell-NP
interactions is required to access all functionalities and
potential degradation related to intracellular fate of
IONPs.
Philosophy behind MRI contrast
Strong magnetic field is applied in MRI that align all
magnetic moments in the direction of field. This creates
balanced magnetization with a magnitude (M
0
)along
z-axis. At resonant frequency, a radio pulse transports
energy to protons which results in switching away
their magnetic moments to their respective z-axis.
Time taken by magnetic moments to come in
equilibrium state called relaxation time. In soft tissues,
magnetic resonance is produced by variations in spin-
spin and spin-net relaxation time of proton and protons
density. Spin net relaxation time (T
1
) is exponential time
constant procedure used to retrieve RF pulse along z-
axis. This procedure causes saturation effect because
before RF pulse full magnetization cannot achieve
(Gogola et al. 2013). After an RF pulse, T
2
is time
exponential constant of latitudinal magnetization. T
2
is linked with time required to align magnetic moments
of protons in xy-plane post RF pulse. This results zero
net magnetic moment in corresponding xy-plane
(Shabestari Khiabani et al. 2016).
Effects of exterior magnetic fields can be removed
with specified spin-echo (SE) arrangements that help in
creating T
1
-orT
2
-weighted contrasts supported by
molecular interplay. Two RF pulses in SE scan provide
flipping angles of 90° and 180° which create spin-echo.
Transverse magnetization is changed with 180° pulse.
Time amongst climax of echo signal and 90° pulse is
named as echo time (Stephen et al. 2011; Shabestari
Khiabani et al. 2016). T
1
contrast agents provide
positive contrast enhancement to T
1
-weighted images
with increased signal strength. T
2
contrast agent
causes negative contrast improvement to T
2
-weighted
images. The existence of paramagnetic ions near water
protons alters T
1
relaxation time and consequently
interaction with water molecules provide enhanced
contrast. Despite extensive usage of gadolinium
chelates, low detection sensitivity, short circulation
time and toxicity issues caused continuous interest
in enhancement of T
2
contrast with superparamagnetic
IONPs (Clarkson 2002; Budde and Frank 2009;Kamaly
and Miller 2010). IONPs show the potential for both T
1
and T
2
contrast; as a result, a lot of interest have been
developed in the last decade.
JNanopartRes (2017) 19:366 Page 9 of 25 366

Principle of MRI
There are two basic imaging modes in MRI; T
1
-weighted
imaging and T
2
-weighted imaging mode. Principle of
MRI is established on aligning of water protons in the
body tissues due to strong applied magnetic field (B
o
)
and precession with the Larmor frequency. Protons
are excited by applying pulse of radiofrequency exactly
at Larmor frequency and align antiparallel to external
applied magnetic field (B
o
) (Fig. 5). This suppresses
longitudinal magnetization while generating transverse
magnetization. Excited protons relaxed to proceed in
ground state with removal of RF pulse through the
following processes: (1) recovery of longitudinal
magnetization as a result of T
1
longitudinal relaxa-
tion, and (2) decay of transverse magnetization
(arises in proton nuclear spins due to loss between
phase coherence and de-phasing) as a result of transverse
relaxation (Shin et al. 2015; Hajba and Guttman 2016).
Local variation in relaxation arises due to proton density,
physical and chemical nature of tissues within specimen.
Typically, superparamagnetic NPs act as T
2
contrast
agent on accumulation in tissues, which provides dark
image with enhanced contrast (Frey et al. 2009).
IONPs-based contrast agents role in MRI
In regenerative medicines, cell therapy offers excellent
pathways for treating injured tissues (Mooney and
Vandenburgh 2008;DiMarinoetal.2013). To improve
and validate cell therapies, cell tracing by noninvasive
means is necessary for in vivo applications. Direct
radioactive imaging, optical gene reporting and MRI
are currently used in cell tracking approaches. Coupling
of MRI with magnetically labeled cells greatly
offer non-invasive and high-resolution cell tracking
ability. Superparamagnetic IONPs in combination
with poly-L-lysine and protamine sulfate as cationic
transfection agents play promising role for developing
iron-deficiency treatments and MR contrasts through
electrostatic interactions (Kircher et al. 2011; Thu et al.
2012;Wangetal.2013; Kim et al. 2016).
With the utilization of active targeting, MRI signals
can be improved significantly with controlled growth of
0
B0= Magnetic field
0= B0
Larmor frequency
Gyromagnetic ratio
X
Z
Y
Mz
X
Z
Y
Mz
Mxy
lanidutignoL
noitazitengaM
Time
Time
Transverse
Ma gnetization
T1effect
T2effect
ab
c
Fig. 5 Schematic summary of MRI principle using IONPs. a
Alignment of spins under applied magnetic field B
0
and precession
under Larmor frequency ω
0
.bSpin relaxation mechanisms of T
1
and T
2
after applying RF pulse. cHypothetical graphs of longitu-
dinal and transverse relaxation with time.
366 Page 10 of 25 J Nanopart Res (2017) 19:366

IONP contrast agents. To further extend the capabilities
of IONP as contrast agents, they are frequently
used with other imaging agents (radio-nucleotide,
fluorescence and CT agents). More than two imaging
agents in multimodal probe imaging areused to improve
diagnosticactivity for producing complementary signals
(Mulder et al. 2007; Fang and Zhang 2009; Thomas
et al. 2013).
In the absence of new imaging tags, multimodal
imaging is also possible by IONPs. At targeted
locations, enhanced imaging techniques (magneto-
motive photoacoustic, magneto-motive ultrasound
and magnetic particle imaging) are used for direct
visualization of IONPs. More precise information about
location and distribution can be obtained by combining
IONPs-based techniques with conventionally used
imaging techniques (fluorescent and MRI). In microwave
imaging (MWI), IONPs can be employed without any
modification to tumor-specified tagging. Microwave
imaging can be divided into two main parts including
standard microwave imaging module and polarizing
magnetic field (PMF). Polarizing magnetic field usually
modulate NPs magnetic susceptibilities in microwave
frequency ranges (Bucci et al. 2015;Shinetal.2015).
IONPs are mostly recognized as magnetic contrast
agent possessing signal void and hypo-intensities on
MR images produced with sequences of regular
pulses (spoiled gradient echo and fast spin echo)
(Wang et al. 2014). Superparamagnetic NPs are also
used as contrast-enhancement agents in molecular
imaging techniques. Magnetite NPs with diameter
smaller than 20 nm are preferred. At biological tem-
perature, their magnetization directions are subjected
to thermal fluctuations. Therefore, randomized value
for their overall magnetization in the absence of
external magnetic field is zero. Less magnetic inter-
actions between NPs suspended in collides provide
stabilized physiological solutions having good NPs
coupling with biological agents (Hao et al. 2010;Xu
and Sun 2013).
Zhang et al. determined bio-distribution and
quantification of iron oxide nanoparticle. They
employed longitudinal relaxation rates/time-based
T
1
contrast for cell targeting, drug delivery and
hyperthermia therapy inside primary clearance organs.
Iron concentration was linearly depending on tissues in
major organs of living organisms, which quantitatively
allowed to probe bio-distribution of IONPs in required
dosage range for MRI techniques (Zhang et al. 2016).
While in another study, synthesized IONPs with no-
table magnetic properties were studied for relaxivity
properties, where monodispersed maghemite NPs
possess less saturation magnetization as compare to
magnetite NPs. Maghemite NPs showed low r
1
(3.00,
3.53 and 10.8 mM
−1
s
−1
) and high r
2
(23.75, 28.26
and 204.2 mM
−1
s
−1
) values for size ranges (3.2, 4.8
and 7.5 nm) respectively (Kolesnichenko et al. 2016).
Stronger effect of transverse relaxivity as compare to
longitudinal makes them suitable candidate in MRI
as positive contrast agents. Superparamagnetic prop-
erties of iron oxide NPs become more prominent
when particle size reduced to 10 nm, that is why they
are preferred for diagnostic purposes. In addition,
there is efficient removal of IONPs at this size after
they settled down in tumor mass via vasculature
leakage (Kucheryavy et al. 2013; Umair et al.
2016). Similarly, Magnitsky et al. generated positive
contrast MRI signal through sweep imaging Fourier
transformation (SWIFT) pulse sequence with IONPs.
Labeled mesenchymal stem cells (MSCs) with differ-
ent concentration of IONPs were examined for cell
proliferation, viability and differentiation. Optimized
SWIFT sequence was used for detection and quanti-
fication of iron concentration present in muscle tis-
sues with injection of labeled MSCs and iron oxide
solution. At flip angle of 10°, maximum contrast
(R
1
= 2.3 ± 0.5 1/s) for 10 days was observed while
lower relaxivity value (1.9 ± 0.7 1/s) for 19 days was
observed at flip angle of 6° (Magnitsky et al. 2017).
Superparamagnetic IONPs are extensively
employed to study T
2
contrast agents in MRI be-
cause negative contrast can enhance the T
2
relaxivity by water protons. To achieve enhanced
T
2
contrast, Chitosan-coated IONPs coupled with
folic acid prepared through incineration method was
investigated (Jing et al. 2008;Chamundeeswarietal.
2013). Whereas substantial drop in signals and forma-
tion of darker images (dark contrast in T
2
-weighted
images) are also reported in literature (Albornoz et al.
2004;Hadjipanayisetal.2008). A similar effect with
increasing iron concentration was observed as well. In
conclusion, incorporation of IONPs as contrast agent in
MRI improve the detection and sensitivity considerably
(Table 1). There are also alloy materials and various
ferrite NPs such as CoFe
2
O
4
,MnFe
2
O
4
,NiFe
2
O
4
probed for negative contrast imaging. Optimization
of IONPs is still in progress with respect to size,
morphology, doping materials, etc.
JNanopartRes (2017) 19:366 Page 11 of 25 366

Magnetite as contrast agent in MRI
Superparamagnetic behavior with low toxicity makes
magnetite (Fe
3
O
4
) NPs, as auspicious candidate for
enzyme immobilization, biosensor, targeted drug
delivery and MRI (Freire et al. 2016). Bare IONPs
can be trapped easily by immune system that prevent
NPs to reach the target. Such type of IONPs oxidized in
air that results in loss of magnetic properties and
dispensability that make them less effective for
intended applications (Remya et al. 2016). Magnetite
NPs due to their prolonged circulation and targeted
imaging emerged as promising candidate for contrast
enhancement in MRI. Longer circulation time can be
maintained by homogenous polymer coatings. These
functionalized magnetite NPs have used in many
diagnostic applications (ultrasound/MR imaging)
(Bae et al. 2010; Zhang et al. 2017).
Bae and co-workers developed dual contrast MRI
agents of gadolinium-based magnetite NPs (GMNPs)
through bio-inspired manner for enhanced T
1
-and
T
2
-weighted images. These NPs were synthesized
through mixed layer formation of dopamine molecules
with poly-ethylene glycol (PEG) by strong coordination
bonds that result in consecutive immobilization on NPs
gadolinium chelates surface. Physical and structural
properties of magnetite NPs was not disturbed by sur-
face modification process that led toward potential
utilization in negative and positive contrasts. Pre-
pared GMNPs had ability of improved T
1
-weighted
image because of high r
1
(11.17 mM
−1
s
−1
)ascom-
pared to magnevist (5.39 mM
−1
s
−1
) already reported
(Bae et al. 2010). Gadolinium-manganese-doped
IONPs have also presented better T
1
and T
2
contrast
effects for liver. Doped iron oxide showed better T
1
contrast enhancement like control gadolinium-
diethylenetriamine penta-acetic acid. It also enhances
T2 contrast image identical to T2 control
superparamagnetic iron oxide contrast agent (Kuo
et al. 2016). These NPs proved very efficient contrast
agent using both T1 and T2 imaging for liver tumor.
Contrast effect can also be manipulated by two pa-
rameters as follows: size and doping. Size effect of
superparamagnetic IONPs have been investigated
with diameter range (4–12 nm). Magnetization
values (25, 43, 80, 120 emug
−1
) have been observed
for water-soluble IONPs with size ranges (4, 6, 9,
12 nm) respectively. This leads towards size-
controlled contrast effects in T
2
-weighted images
due to size-dependent magnetization. Similarly,
IONPs with enhanced magnetic properties can exten-
sively govern with doping of different transition
metals (Huh et al. 2005). Beg et al. (2017)synthe-
sized porous Fe
3
O
4
@SiO
2
nanorods with a diameter
of 180 nm and length of 520 nm with significantly
enhanced r
2
relaxivity values of 192 mM
−1
s
−1
.Sig-
nificant signal attenuation was observed with in-
crease in concentration of iron from 0.06 to
0.18 mM (Fig. 6a–d). Magnetite is the most widely
exploited oxidation state of IONPs due to its higher
stability. Preparation methods are simpler because
oxidation can take place in the open reaction and
IONPs supposed to remain relatively stable in the
biological environment (Table 2).
Maghemite as contrast agent in MRI
Maghemite have two nonequivalent magnetically
interpenetrating sublattices that make it promising
candidate because of their strong magnetic behavior
Tabl e 1 Transverse relaxation values of iron oxide core polymer shell-based NPs
Magnetic core Coating
(reference)
D
H
(nm) D
TEM
(nm) r
2
(mM
−1
s
−1
)M
s
(emug
−1
)B(T)
Fe/NiFe
2
O
4
DMSA (Bhosale et al. 2012; Blanco-Andujar et al. 2016;
Dong et al. 2017)
45 16 260 142 0.47
Fe/MnFe
2
O
4
DSMA (Safontseva and Nikiforov 2001;Yoonetal.2011;
Lee and Hyeon 2012)
45 16 356 146 0.47
Fe/CoFe
2
O
4
DMSA (Huang et al. 2013; Blanco-Andujar et al. 2016;
Weissleder et al. 2017)
45 16 243 133 0.47
α-Fe/Fe
3
O
4
DMSA (Brahma et al. 2002;Cheongetal.2011;
Zelina et al. 2012)
16 324 140 9.4
Bcc Fe/Fe
3
O
4
PEG (Lacroix et al. 2011;Yuetal.2011;
Wang et al. 2012b)
40–45 15 220 164 3
366 Page 12 of 25 J Nanopart Res (2017) 19:366

in biological and biomedical applications especially for
contrast enhancement in MRI (Wang et al. 2001;
Alexiou et al. 2006). Maghemite NPs are frequently
used as negative contrast agents in MRI (Wang et al.
2001;Kluchovaetal.2009). Properties of maghemite
NPs have been extensively studied (Rabias et al. 2008;
Rozanova and Zhang 2013), where size, surface, struc-
ture, chemical composition and morphology depends on
different synthesis conditions. Contrast agents based on
typical maghemite NPs are widely introduced to image
the functional and anatomical regions with alteration of
relaxation times between normal and effected tissues.
Fig. 6 a–dPorous magnetite-SiO
2
core shell nanorods. aTEM
micrograph of magnetite-SiO
2
nanorods. bContrast features of
nanorods at different iron concentrations. cr
2
plot against iron
concentration. dMR images of HeLa cells after 24-h incubation
(Adopted with permission from (Beget al. 2017)). e,fSiO
2
-coated
iron oxide nanoeyes. eTEM image of maghemite IONPs encap-
sulated in SiO2 shell. fCalculated r
2
values for different Fe
concentrations. MR image at different Fe concentrations (inset)
(reprinted with permission from Chen et al. (2014); Copyright
(2014) American Chemical Society).
Tabl e 2 Reported dual contrast (Blanco-Andujar et al. 2016)agents
Nano-particle (Core@shell) Coating
(reference)
D
TEM
(nm)
r
1
(mM
−1
s
−1
)
r
2
(mM
−1
s
−1
)
r
2
/r
1
B(T)
Fe
3
O
4
/SiO
2
/Gd
2
O(CO
3
)
2
(Jang et al. 2009; Leao Andrade et al. 2015;
Yang et al. 2015a;Nizameevetal.2017)
21.5 3.7 312 84 3
Fe
3
O
4
@SiO
2
(Gd-DTPA) DPTA (Ding et al. 2004; van Schooneveld
et al. 2008;Yangetal.2011)
27 4.2 17.4 4.1 3
Fe
3
O
4
@Al(OH)
3
BP-PEG (Zhao et al. 2010a; Cui et al. 2014) 4.9 121.9 24.8 3
JNanopartRes (2017) 19:366 Page 13 of 25 366

Superparamagnetic maghemite NPs enhances predomi-
nantly T
2
relaxation time (Rabias et al. 2015).
Dextran-coated ultra-small maghemite NPs were
prepared with modified co-precipitation method at
low temperature. Precise control on reaction time
and temperature were maintained for narrow size
distribution of NPs. Synthesized Gd-DTPA NPs ex-
hibit high relaxivity values (r
1
>6mM)thatmake
them effective contrast agents in MRI tomography as
well as in computer tomography (Rabias et al. 2015).
Major principle in formation of maghemite is hydrolysis
ratio when synthesized by polyol process. Measured
values for hydrodynamic radius and relaxivities (r
1
and r
2
)forγ-Fe
2
O
3
-DA coatings were 21 nm,
12.8 mM
−1
s
−1
and 33.6 mM
−1
s
−1
reported respectively.
Whereas hydrodynamic radius and relaxivity (r
1
)forγ
Fe
2
O
3
-DA coatingwas reported95 nm and 7.3 mM
−1
s
−1
respectively (Basti et al. 2010).
Superparamagnetic maghemite (γ-Fe
2
O
3
)NPs
were used for obtaining effective contrast effects
through middle ear to inner ear. Mediated oxidation
of ceric ammonium nitrate generated superparamagnetic
γ-Fe
2
O
3
NPs. Hydrodynamic radius, potential, satura-
tion magnetization, relaxivity (r
1
,r
2
) values for
superparamagnetic (γ-Fe
2
O
3
) NPS were (50–60 nm),
155.2 mV, 75.2 emu/g, 0.0015 mM
−1
s
−1
and
189 mM
−1
s
−1
respectively (Zou et al. 2016). Liu et al.
synthesized superparamagnetic iron oxide
Fe
3
O
4
@(α,γ)Fe
2
O
3
with one step approach by
solvothermal method. At room temperature, no
alteration in novel superparamagnetic properties
were observed. Unique superparamagnetic ferromagnetic
transitions of Fe
3
O
4
@(α,γ)Fe
2
O
3
at 30 K can be actively
used as contrast agents. Low values of transverse
relaxivity (0.0358 mM
−1
s
−1
) were reported (Liu
et al. 2016). Maghemite encapsulated in SiO
2
NPs
also presented higher r
2
values (285 mM
−1
s
−1
).
These nanoeyes (Fig. 6e, f) were polymerized by
poly-L-lysine and sodium alginate.
With one-step approach of thermal decomposition
method, monodispersed NPs of maghemite with size
ranges (15–20 nm) were prepared. Maghemite NPs
were dispersed in bentonite matrix for MRI diagnostics.
Resultant nanocomposites play effective role in negative
oral contrast agents in gastrointestinal track for MRI
(Kluchova et al. 2009). Tunable ultra-small-sized
superparamagnetic IONPs coated with polyethylene
glycol phosphonate moieties with size range (3–9nm)
fabricated for neovascularization MRI. Their r
2
relaxivity values were (8.9, 95.5, and 188.3 mM
−1
s
−1
)
for synthesis temperature (170, 210 and 250 °C)
respectively (Richard et al. 2016). Although many
studies have been reported based on maghemite
NPs, stability is still a big issue with these NPs
and special solvent conditions are necessary to maintain
their oxidation state. In many cases, cent percent
maghemite NPs are not obtained and reaction produce
both complex of magnetite and maghemite NPs that
hinders to know the exact effect of maghemite NPs on
the contrast enhancement.
Hematite as contrast agents
Fewer studies have been reported for hematite as
potential candidate of contrast enhancement in MRI due
to many constraints such as stability, monodispersity, etc.
(Guardia et al. 2007; Saeidian et al. 2009). Chen et al.
synthesized magnetic nanocapsules of stabilized iron
core with mesoporous silica shell. Synthesis of these
nanocapsules involves encapsulation of ellipsoidal
hematite in silica achieved with partial etching of
hematite core. These hematite cores provide high
values of saturation magnetization along with high
relaxivity (r
1
=8.6mM
−1
s
−1
and r
2
=285mM
−1
s
−1
)
that served as MRI contrast agents (Chen et al. 2014).
Single-wall carbon nanotubes having hematite traces
were functionalized by covalent carboxylic acid and
non-covalent lipid-PEG. For 0.07% iron content,
transversal relaxivity value (r
2
= 10,194 mM
−1
s
−1
)
was reported (Doan et al. 2012). Hematite NPs dissolute
very rapidly under acidic pH conditions as a result
separate use is not very feasible and have been utilized
with other stabilized materials. This reason limits the use
of hematite NPs in the MRI.
Contrast agents based on assembled IONPs
At nanoscale, physical properties can be considerably
modified by the behavior of the NPs in the biological
environment or during their systematic administration
(Nie et al. 2010; Tassa et al. 2011; Lee and Hyeon 2012).
Commonly, assembled IONPs possess significantly
high relaxivity values as compared to individually
well-dispersed NPs. Iron oxide self-assembled with
polymers and matrices of meso-porous silica have
developed as novel bio-responsive and multifunctional
nanoplatforms for various biomedical application in
MRI (Piao et al. 2008; Kim et al. 2009;Lingetal.2015).
366 Page 14 of 25 J Nanopart Res (2017) 19:366

Fluorescent-based superparamagnetic IONPs was re-
ported as one of the most stabilized contrast agents as
compared with the commercially available contrast
agents. To obtain more stability, contrast agents are
usually designed with covalent linkages in physiological
medium (Eghbali et al. 2016). Theoretically, estimated
maximum relaxivity (r
2
) of IONPs was attained with
ferrimagnetic iron oxide nanocubes by optimizing over-
all size with 22 nm edge length. In aqueous media, these
nanocubes encapsulated with PEG-phospholipids ex-
hibited greater colloidal stability. Nanocubes are consid-
ered biocompatible for T
2
contrast agents with no effects
on cell viability up to 0.75 mg Fe/ml concentration
which results to very high relaxivity (761 mM
−1
s
−1
).
With 3-T MR clinical scanner, these nanostructures with
high relaxivity were successfully used to perform
in vivo tumor MRI by intravenous injection (Lee et al.
2012). Yang et al. synthesized europium-doped iron
oxide nanocubes of diameter 14 nm for contrast imag-
ing. These nanocubes showed higher r
1
values as com-
pared to iron oxide (Fe
3
O
4
), although r
2
values were
slightly lower than magnetite NPs (Fig. 7g–i) (Yang
et al. 2015b). Another example of unconventional mor-
phology is octapod IONPs (Fig. 7a–c). These unique
Fig. 7 a–cOctapod-shaped IONPs. aLow resolution TEM mi-
crograph (Edge length 30 nm). bMR micrographs of octapod-
shaped iron oxide and spherical NPs inside liver tumor model at
different times. cThe liver to tumor quantification of octapod and
spherical NPs (reproduced with permission from Zhao et al.
(2013)). d–fMulticore iron oxide. dBright field TEM image of
28.8 ± 0.18 nm size nanoflowers. eMR images of MCF-7 cells
dispersed in agarose gels labeled with multicore NPs (upper line)
and BNF-starch (bottom line), (F) r
1
and r
2
relaxivities compari-
sons of different sizes multicore NPs, MC0 (24 ± 0.19 nm), MC1
(28.8 ± 0.18 nm), MC2 (22.2 ± 0.22 nm), MC3 (19.7 ± 0.17 nm),
SC (10.3 ± 0.30 nm), MC (multi-core), SC (spherical core)
(reprinted with permission from Lartigue et al. (2012); Copyright
(2012) American Chemical Society). g–iEuropium-iron oxide
nanocubes. gTEM image (20.1 ± 2.4 nm), hT2 MR-weighted
images of respective cancer cell lines SMMC-7721 for different
concentrations of europium iron oxide nanocubes and IONPs. iT
2
-
weighted MR images of liver at 3 T. T
2
contrast considerably
150 min post injection (adopted from (Yang et al. 2015b)with
permission).
JNanopartRes (2017) 19:366 Page 15 of 25 366

structures showed r
2
values (679.3 mM
−1
s
−1
)(Zhao
et al. 2013).
Multi-core maghemite NPs synthesized by single-
step hydrolysis approach under high temperature condi-
tions also showed enhanced MRI contrast effects. High
r
2
relaxivity values (365 mM
−1
s
−1
) were observed for
multi-core NPs as compared to single-domain spherical
NPs having relaxivity values (33–67 mM
−1
s
−1
). High r
2
relaxivities for stabilized hydrogel NP clusters (300–
500 mM
−1
s
−1
) provide enhanced T
2
contrast (Lartigue
et al. 2012)(Fig.7d–f). Zwitterion-coated gadolinium-
embedded iron oxide exhibited high T
1
contrast effect
for imaging purposes to detect tumor vie enhanced
retention effect, permeation and clearing ability in living
objects. Enhanced T
1
contrast effect was achieved with
combination of gadolinium species with spin coating
effect. This method provides highly sensitive and
effective IONPs-based contrast agents that provides
efficient passive tumor targeting with long circulation
time period (Zhou et al. 2013).
Systematically developed PEGylated iron oxide-
based T
1
contrast agent with adjustable crystalline core
size provides excellent relaxometric properties. Under
physiological conditions, optimized and dense coatings
of PEGylated iron oxide potentially used as T
1
contrast
with minimum toxicity and high stability (Tromsdorf
et al. 2009). To provide multifunctional effective con-
trast agents with different coatings such as polyol
(Bomati-Miguel et al. 2014), silica (Iqbal et al. 2015;
Haynes et al. 2016; Hurley et al. 2016), gold (Tarin et al.
2015; Azhdarzadeh et al. 2016; Rubio-Navarro et al.
2016), dopamine (Wu et al. 2015b), citrate (Poller et al.
2016), ethyleneglycol (Ramniceanu et al. 2016),
IONPs-based gadolinium (Szpak et al. 2014;Chen
et al. 2015) and fluorinated based NPs (Palekar et al.
2015) have been reported in literature. In recent years,
unconventional morphologies of the IONPs have shown
much improved T2 imaging contrast than conventional
spherical nanoparticles. Nanocubes, nanoflowers, trian-
gles and other assemblies with materials increased the
detection signal many folds. These assemblies have
increased the potential use of IONPs as T1 contrast
agent as well (Table 3).
Parameters controlling contrast enhancement
Important parameter that can strongly influence contrast
properties of IONPs is magnetic properties. Magnetic
properties play prominent role in contrast because
square of magnetic moments is directly proportional to
the relaxation rate (r
2
). At the same time, saturation
magnetization depends on NPs shape, size and compo-
sition. Effect of IONPs size on relaxivity has been
reportedinliterature(Joshietal.2009; Smolensky
et al. 2013). Magnetic moments decreases strongly
along with surface spin disorder as size of IONPs re-
duces up to 5 nm (Kim et al. 2011;Zengetal.2012). To
increase the saturation magnetization, alternative strate-
gy is tuning of composition of IONPs. Transverse
relaxivity values for different NPs have been reported
in literature according to their size, composition, shape
and saturation magnetization (Lee et al. 2007; Yoon
et al. 2011;Wangetal.2012a).
Compositional effect
Magnetic NPs composition greatly affect capabilities of
contrast because it dominantly controls magnetic
moments at atomic scale. Magnetic moment in
IONPs preferably used as T
2
-weighted contrast MRI
agents that can be changed with metal ions incorpora-
tion in iron oxide. Jae-Hyun et al. reported ferrites
exhibiting different magnetic properties with different
Tabl e 3 Relaxivity values for nanocube iron oxide (Blanco-Andujar et al. 2016) based particles
Magnetic core Coating
(reference)
D
H
(nm) D
TEM
(nm) r
2
(mM
−1
s
−1
)M
s
(emug
−1
)B(T)
Iron oxide PEG phospholipid (Laurent et al. 2008;
Tong et al. 2010; Lee et al. 2011)
–57.8 324 132.1 1.5
Co
0.5
Fe
1.5
O
4
PMAO (William et al. 2006; Ferguson
et al. 2015;Sathyaetal.2016)
–20 958 60 1.5
Iron oxide PEG phospholipid (Nitin et al. 2004;
Thorek et al. 2006; Lee et al. 2012)
43 22 761 05 3
Europium-iron oxide Citrate (Kahn et al. 2002; Long and
Grandjean 2013; Nachimuthu et al. 2014)
–14 97.52 39.6 0.5
366 Page 16 of 25 J Nanopart Res (2017) 19:366

mass magnetization values because of cationic doping at
the respective octahedral sites. MnFe
2
O
4
NPs exhibit
high relaxivity values (~ 358 mM
−1
s
−1
) due to high
magnetization value at 1.5 T (Jae-Hyun et al. 2007).
Whereas at tetrahedral site, Zn
2+
dopants will again lead
toward high magnetization values at 4.7 T with high
relaxivity values (860 mM
−1
s
−1
) (Jang et al. 2009).
Further investigation due to the composition effects with
dopants (e.g. Gd
2
O
3
,MnO,GdF
3
)reportshorteningT
1
longitudinal relaxation time (Hadjipanayis et al. 2008;
Hao et al. 2010).
Effect of Surface Properties
MRI contrast came from the difference in signals that
reside in different environments due to water molecules
interactions. Interaction between magnetic NPs and wa-
ter molecules primarily occur on NPs surface. Magnetic
properties and enhancement of MRI contrast is influ-
enced due to surface properties of NPs, i.e. surface
charge, surface roughness, etc. For in vivo applications,
biocompatible magnetic NPs are developed with coating
of functionalizing and stabilizing agent. These coating
moieties can affect water molecules relaxation proper-
ties in many forms including increase in hydrodynamic
diameter, hydrogen binding, diffusion and hydration.
Duan et al. investigate and suggest that MRI contrast
effects are enhanced due to hydrophilic coatings on
surfaces of NPs. IONPs coated with copolymers at
different hydrophilicity levels including hyperbranched
polyethylenimine, octadecene, poly (maleic acid), PEG
grated polyethylenimine greatly effect proton relativities
values (Shin et al. 2009). Direct exchange of multivalent
ligands with hydrophobic surface ligands make more
access of water to the respective magnetic cores, as a
result rapid diffusion and exchange between adjacent
layers of NPs and bulk phase occur. Duan et al. reported
high relaxivity value of PEI hydrophilic polymer with
IONPs having size of 10 nm (Duan et al. 2008).
Size Effect
Relaxation rate dependency on NPs size have been
studied theoretically and experimentally. Then, r
2
relaxivity in magnetically induced inhomogeneous en-
vironment is generally predicted in two regimes. Proton
diffusion due to smaller NPs is faster in comparison to
frequency resonance shift and consequently produce
independent T
2
. Predicted relaxivity values are identical
in this region called motional averaging regime (Brooks
et al. 2001; Huang et al. 2012). In this regime, transverse
relaxivity value observed to be increase with increase in
NPs size. Proton diffusion factor for larger particles is
non-dominant for signal decay due to stronger
perturbing field that make 1/T
2
relaxation rate independent
to diffusion. In this regime, transverse relaxivity values
observed to be decrease with increase in NPs size. This
process is named as static dephasing regime (Jae-Hyun
et al. 2007; Jun et al. 2008a,b).
Conclusion, challenges and outlook
In this article, we critically focused on contrast agents
based on IONPs. We reviewed MR relaxivity of IONPs
for biocompatible T
1
contrast agents alongside highly
sensitive T
2
contrast agents. However, their large-scale
use has still to be fulfilled because of current limitations
of detection sensitivity and inefficiency of tissue speci-
ficity. For effective in vivo applications, IONPs with
size ~ 4 nm are preferred for assurance of long blood
circulation time. For attaining high relaxivity values, it is
very critical because T
2
strongly depends on magnetic
moments, that are directly related to size and volume
control of nanoparticles. To obtain optimal results, dis-
tribution of surface ligands should delicately be
controlled.
Although toxicity of polymer coatings has been
studied extensively, prompt formation of protein corona
after injection is also an important factor and many
groups are considering this parameter because this can
certainly hamper the contrast properties in vivo. Further
enhancement in contrast effects of IONPs with modified
magnetic properties can be achieved by narrow size
distribution, irregular morphologies and doping by
transition metals.
Another limitation of IONPs efficiency is inaccurate
quantification and targeting at single molecule level for
cellular disorders. Next challenge is to use nanotechnology
based materials for diagnostic purposes at single
atom/molecule level. So, it is essential to design
such strategies to enable IONPs for recognition of special
surface signatures for targeted cells to access specific
organelles for excellent contrast. To overcome this
problem, extensive studies/experiments on IONPs
are needed. Clinical availability of such synthesized
JNanopartRes (2017) 19:366 Page 17 of 25 366

NPs is still ambiguous. In clinical translation, IONPS
should clearly be addressed with ligands and magnetic
core materials for their pharmacokinetics profiles with
long-term toxicity.
Acknowledgements The authors acknowledge the Higher
Education Commission Pakistan for financial support under
NRPU project No. 6411.
Compliance with ethical standards
Conflict of interest The authors declare that they have no
conflict of interest.
References
Aggarwal P, Hall JB et al (2009) Nanoparticle interaction with
plasma proteins as it relates to particle biodistribution, bio-
compatibility and therapeutic efficacy. Adv Drug Deliv Rev
61(6):428–437
Albornoz C, Sileo EE et al (2004) Magnetic polymers of
maghemite (γ-Fe
2
O
3
) and polyvinyl alcohol. Phys B
Condens Matter 354(1):149–153
Alexiou C, Jurgons R et al (2006) Medical applications of mag-
netic nanoparticles. J Nanosci Nanotechnol 6(9-10):2762–
2768
Arshad M, Siddiqui HA et al (2016) Synthesis of iron oxide
magnetic nanoparticle by sol-gel method and their char-
acterization. Professor Dr. Muhammad Tufail Convener
98:98
Azhdarzadeh M, Atyabi F et al (2016) Theranostic MUC-1
aptamer targeted gold coated superparamagnetic iron oxide
nanoparticles for magnetic resonance imaging and
photothermal therapy of colon cancer. Colloids Surf B
Biointerfaces 143:224–232
Ba-Abbad MM, Takriff MS et al (2017) Size and shape controlled
of α-Fe2O3 nanoparticles prepared via sol–gel technique and
their photocatalytic activity. J Sol-Gel Sci Technol 81(3):
880–893
Baaziz W, Pichon BP et al (2014) Magnetic iron oxide nanoparti-
cles: reproducible tuning of the size and nanosized-dependent
composition, defects, and spin canting. J Phys Chem C
118(7):3795–3810
Bae KH, Kim YB et al (2010) Bioinspired synthesis and charac-
terization of gadolinium-labeled magnetite nanoparticles for
dual contrast T 1-and T 2-weighted magnetic resonance
imaging. Bioconjug Chem 21(3):505–512
Bagwe R, Kanicky J et al (2001) Improved drug delivery using
microemulsions: rationale, recent progress, and new hori-
zons. Crit Rev Ther Drug Carrier Syst 18(1):77
Basak S, Chen D-R et al (2007) Electrospray of ionic precursor
solutions to synthesize iron oxide nanoparticles: modified
scaling law. Chem Eng Sci 62(4):1263–1268
Bashir M, Riaz S et al (2014) Magnetic Properties of Fe 3 O 4
Stabilized Zirconia. IEEE Trans Magn 50(8):1–4
Basti H, Tahar LB et al (2010) Catechol derivatives-coated Fe 3 O 4
and γ-Fe 2 O 3 nanoparticles as potential MRI contrast agents. J
Colloid Interface Sci 341(2):248–254
Beg MS, Mohapatra J et al (2017) Porous Fe 3 O 4-SiO 2
core-shell nanorods as high-performance MRI contrast
agent and drug delivery vehicle. J Magn Magn Mater
428:340–347
Bermudez E, Mangum JB et al (2004) Pulmonary responses of mice,
rats, and hamsters to subchronic inhalation of ultrafine titanium
dioxide particles. Toxicol Sci 77(2):347–357
Bhavani P, Rajababu C et al (2016) Synthesis and characterization
of iron oxide nanoparticles prepared hydrothermally at dif-
ferent reaction temperatures and pH. Int J Mater Res 107(10):
942–947
Bhosale RR, Kumar A et al (2016) Propylene oxide assisted sol–
gel synthesis of zinc ferrite nanoparticles for solar fuel pro-
duction. Ceram Int 42(2):2431–2438
Bhosale RR, Shende RV et al (2012) Sol-gel derived NiFe 2 O 4
modified with ZrO 2 for hydrogen generation from solar
thermochemical water-splitting reaction. MRS Online
Proceedings Library Archive:1387
Blanco-Andujar C, Walter A et al (2016) Design of iron oxide-
based nanoparticles for MRI and magnetic hyperthermia.
Nanomedicine 11(14):1889–1910
Bomati-Miguel O, Miguel-Sancho N et al (2014) Ex vivo assess-
ment of polyol coated-iron oxide nanoparticles for MRI diag-
nosis applications: toxicological and MRI contrast enhance-
ment effects. J Nanopart Res 16(3):1–13
Bomatí-Miguel O, Morales MP et al (2005) Fe-based
nanoparticulate metallic alloys as contrast agents for
magnetic resonance imaging. Biomaterials 26(28):
5695–5703
Bondarenko O, Juganson K et al (2013) Toxicity of Ag, CuO and
ZnO nanoparticles to selected environmentally relevant test
organisms and mammalian cells in vitro: a critical review.
Arch Toxicol 87(7):1181–1200
Brahma P, Banerjee S et al (2002) Properties of nanocompos-
ites of α-Fe and Fe 3 O 4. J Magn Magn Mater 246(1):
162–168
Brooks RA, Moiny F et al (2001) On T2-shortening by weakly
magnetized particles: the chemical exchange model. Magn
Reson Med 45(6):1014–1020
Brunner TJ, Wick P et al (2006) vitro cytotoxicity of oxide
nanoparticles: comparison to asbestos, silica, and the effect
of particle solubility. Environ Sci Technol 40(14):4374–4381
Bucci OM, Crocco L et al (2015) On the optimal measurement
configuration for magnetic nanoparticles-enhanced breast
cancer microwave imaging. IEEE Trans Biomed Eng 62(2):
407–414
Budde MD, Frank JA (2009) Magnetic taggingof therapeutic cells
for MRI. J Nucl Med 50(2):171–174
Bulte JW, Kraitchman DL (2004) Iron oxide MR contrast agents
for molecular and cellular imaging. NMR Biomed 17(7):
484–499
Cedervall T, Lynch I et al (2007) Understanding the nanoparticle–
protein corona using methods to quantify exchange rates and
affinities of proteins for nanoparticles. Proc Natl Acad Sci
104(7):2050–2055
366 Page 18 of 25 J Nanopart Res (2017) 19:366

Chamundeeswari M, Sastry T et al (2013) Iron nanoparticles from
animal blood for cellular imaging and targeted delivery for
cancer treatment. Biochim Biophys Acta Gen Subj 1830(4):
3005–3010
Chatterjee S, Sarkar K (2013) A computational and mathematical
approach towards the design and synthesis of uniform Au
seed decorated Fe 3 O 4 nanoparticle for potential bio-appli-
cation. Procedia Technol 10:457–463
Chen D-H, He X-R (2001) Synthesis of nickel ferrite nanoparticles by
sol-gel method. Mater Res Bull 36(7):1369–1377
Chen F, Gerion D (2004) Fluorescent CdSe/ZnS nanocrystal–
peptide conjugates for long-term, nontoxic imaging and nu-
clear targeting in living cells. Nano Lett 4(10):1827–1832
Chen G, Chen W et al (2009) MRI-visible polymeric vector bearing
CD3 single chain antibody for gene delivery to T cells for
immunosuppression. Biomaterials 30(10):1962–1970
Chen H, Sulejmanovic D et al (2014) Iron-loaded magnetic
nanocapsules for pH-triggered drug release and MRI imag-
ing. Chem Mater 26(6):2105–2112
Chen R, Ling D et al (2015) Parallel comparative studies on mouse
toxicity of oxide nanoparticle-and gadolinium-based T1 MRI
contrast agents. ACS Nano 9(12):12425–12435
Chen X, Gambhir SS et al (2011) Theranostic nanomedicine. Acc
Chem Res 44(10):841–841
Cheng C, Xu F et al (2011) Facile synthesis and morphology evolu-
tion of magnetic iron oxide nanoparticles in different polyol
processes. New J Chem 35(5):1072–1079
Cheong S, Ferguson P et al (2011) Simple synthesis and
functionalization of iron nanoparticles for magnetic res-
onance imaging. Angew Chem Int Ed 50(18):4206–
4209
Chin AB, Yaacob II (2007) Synthesis and characterization of
magnetic iron oxide nanoparticles via w/o microemulsion
and Massart's procedure. J Mater Process Technol 191(1):
235–237
Clapsaddle BJ, Gash AE et al (2003) Silicon oxide in an iron
(III) oxide matrix: the sol–gel synthesis and characteriza-
tion of Fe–Si mixed oxide nanocomposites that contain
iron oxide as the major phase. J Non-Cryst Solids 331(1):
190–201
Clarkson R (2002) Blood-pool MRI contrast agents: properties and
characterization. Springer, Contrast Agents I, pp 201–235
Colvin, V. (2003). The potential environmental impact of
engineered nanomaterials. Nat Biotechnol 21:1166–1170.
Find this article online.
Couture P, Williams G et al (2017) Nanocrystalline
multiferroic BiFeO 3 thin films made by room tempera-
ture sputtering and thermal annealing, and formation of
an iron oxide-induced exchange bias. J Alloys Compd
695:3061–3068
Cui H, Liu Yet al (2013) Structure switch between α-Fe 2 O 3, γ-
Fe 2 O 3 and Fe 3 O 4 during the large scale and low
temperature sol–gel synthesis of nearly monodispersed iron
oxide nanoparticles. Adv Powder Technol 24(1):93–97
Cui X, Belo S et al (2014) Aluminium hydroxide stabilised MnFe 2 O
4 and Fe 3 O 4 nanoparticles as dual-modality contrasts agent for
MRI and PET imaging. Biomaterials 35(22):5840–5846
Dalle-Donne I, Rossi R et al (2007) S-glutathionylation in
protein redox regulation. Free Radic Biol Med 43(6):
883–898
David B, Pizúrová N et al (2004) Preparation of iron/graphite
core–shell structured nanoparticles. J Alloys Compd 378(1):
112–116
De Montferrand C, Hu L et al (2013) Iron oxide nanoparticles with
sizes, shapes and compositions resulting in different magne-
tization signatures as potential labels for multiparametric
detection. Acta Biomater 9(4):6150–6157
Di Carlo L, Conte DE et al (2014) Microwave-assisted fluorolytic
sol–gel route to iron fluoride nanoparticles for Li-Ion batte-
ries. Chem Commun 50(4):460–462
Díaz B, Sánchez-Espinel C et al (2008) Assessing methods for
blood cell cytotoxic responses to inorganic nanoparticles and
nanoparticle aggregates. Small 4(11):2025–2034
DiMarino AM, Caplan AI et al (2013) Mesenchymal stem cells in
tissue repair. Front Immunol 4:201
Ding Y, Hu Y et al (2004) Polymer–monomer pairs as a
reaction system for the synthesis of magnetic Fe3O4–
polymer hybrid hollow nanospheres. Angew Chem Int
Ed 43(46):6369–6372
Doan BT, Seguin J et al (2012) Functionalized single-walled
carbon nanotubes containing traces of iron as new negative
MRI contrast agents forin vivo imaging. Contrast Media Mol
Imaging 7(2):153–159
Dobrovolskaia MA, Patri AK et al (2009) Interaction of colloidal
gold nanoparticles with human blood: effects on particle size
and analysis of plasma protein binding profiles. Nanomed:
Nanotechnol, Biol Med 5(2):106–117
Dong Y, Wang H et al (2017) Electrical and hydrogen reduction
enhances kinetics in doped zirconia and ceria: I. grain growth
study. J Am Ceram Soc 100(3):876–886
Duan H, Kuang M et al (2008) Reexamining the effects of particle
size and surface chemistry on the magnetic properties of iron
oxide nanocrystals: new insights into spin disorder and pro-
ton relaxivity. J Phys Chem C 112(22):8127–8131
Dürr S, Janko C et al (2013) Magnetic nanoparticles for cancer
therapy. Nanotechnol Rev 2(4):395–409
Duzgunes N, DüzgüneşN (2012) Nanomedicine: Infectious
Diseases. Immunotherapy, Diagnostics, Antifibrotics,
Toxicology and Gene Medicine, Elsevier
Eghbali P, Fattahi H et al (2016) Fluorophore-tagged
superparamagnetic iron oxide nanoparticles as bimodal con-
trast agents for MR/optical imaging. J Iran Chem Soc 13(1):
87–93
Fang C, Zhang M (2009) Multifunctional magnetic nanoparticles
for medical imaging applications. J Mater Chem 19(35):
6258–6266
Ferguson RM, Khandhar AP et al (2015) Magnetic particle imag-
ing with tailored iron oxide nanoparticle tracers. IEEE Trans
Med Imaging 34(5):1077–1084
Fornara A, Johansson P et al (2008) Tailored magnetic
nanoparticles for direct and sensitive detection of bio-
molecules in biological samples. Nano Lett 8(10):3423–
3428
Freire T, Dutra L et al (2016) Fast ultrasound assisted synthesis of
CHITOSAN-based magnetite NANOCOMPOSITES as a
modified electrode sensor. In: Carbohydrate Polymers
Frey NA, Peng S et al (2009) Magnetic nanoparticles: synthesis,
functionalization, and applications in bioimaging and magnetic
energy storage. Chem Soc Rev 38(9):2532–2542
JNanopartRes (2017) 19:366 Page 19 of 25 366

Gautam A, van Veggel FC (2013) Synthesis of nanoparticles, their
biocompatibility, and toxicity behavior for biomedical appli-
cations. J Mater Chem B 1(39):5186–5200
Gessner A, Lieske A et al (2002) Influence of surface charge
density on protein adsorption on polymeric nanoparticles:
analysis by two-dimensional electrophoresis. Eur J Pharm
Biopharm 54(2):165–170
Gessner A, Lieske A et al (2003) Functional groups on polystyrene
model nanoparticles: influence on protein adsorption. J
Biomed Mater Res A 65(3):319–326
Glasgow W, Fellows B et al (2016) Continuous synthesis of iron
oxide (Fe 3 O 4) nanoparticles via thermal decomposition.
Particuology 26:47–53
Gogola D, Štrbák O et al (2013) Contrast agents based on magnetic
nanoparticles and its interaction with surrounding environment
during contrast imaging. MEASUREMENT:299–302
Grabinski CM, Salaklang J et al (2014) Multifunctionalized spions
for nuclear targeting: cell uptake and gene expression. Nano
9(01):1450009
Gref R, Lück M et al (2000) ‘Stealth’corona-core nanoparti-
cles surface modified by polyethylene glycol (PEG): in-
fluences of the corona (PEG chain length and surface
density) and of the core composition on phagocytic up-
take and plasma protein adsorption. Colloids Surf B
Biointerfaces 18(3):301–313
Guardia P, Batlle-Brugal B et al (2007) Surfactant effects in
magnetite nanoparticles of controlled size. J Magn Magn
Mater 316(2):e756–e759
Gupta AK, Curtis AS (2004) Surface modified superparamagnetic
nanoparticles for drug delivery: interaction studies with hu-
man fibroblasts in culture. J Mater Sci Mater Med 15(4):493–
496
Gupta AK, Gupta M (2005) Synthesis and surface engineering of
iron oxide nanoparticles for biomedical applications.
Biomaterials 26(18):3995–4021
Gupta AK, Wells S (2004) Surface-modified superparamagnetic
nanoparticles for drug delivery: preparation, characterization,
and cytotoxicity studies. IEEE Trans Nanobioscience 3(1):66–
73
Gutiérrez L, Costo R et al (2015) Synthesis methods to prepare
single-andmulti-core iron oxide nanoparticles for biomedical
applications. Dalton Trans 44(7):2943–2952
Hachani R, Lowdell M et al (2016a) Correction: polyol synthesis,
functionalisation, and biocompatibility studies of
superparamagnetic iron oxide nanoparticles as potential
MRI contrast agents. Nanoscale 8(7):4395
Hachani R, Lowdell M et al (2016b) Polyol synthesis, functional-
isation, and biocompatibility studies of superparamagnetic
iron oxide nanoparticles as potential MRI contrast agents.
Nanoscale 8(6):3278–3287
Hadjipanayis CG, Bonder MJ et al (2008) Metallic iron nanopar-
ticles for MRI contrast enhancement and local hyperthermia.
Small 4(11):1925–1929
Hajba L, Guttman A (2016) The use of magnetic nanoparticles in
cancer theranostics: toward handheld diagnostic devices.
Biotechnol Adv 34(4):354–361
Halliwell B, Gutteridge JM (2015) Free radicals in biology and
medicine. Oxford University Press, USA
Hao R, Xing R et al (2010) Synthesis, functionalization, and
biomedical applications of multifunctional magnetic nano-
particles. Adv Mater 22(25):2729–2742
Harisinghani MG, Barentsz J et al (2003) Noninvasive detection of
clinically occult lymph-node metastases in prostate cancer. N
Engl J Med 348(25):2491–2499
Haynes CL, Hurley KR et al (2016) Mesoporous silica-coated
nanoparticles. US Patent 20,160 051:471
Hoshino A, Fujioka K et al (2004) Physicochemical properties and
cellular toxicity of nanocrystal quantum dots depend on their
surface modification. Nano Lett 4(11):2163–2169
Huang H, Zhang X-F et al (2013) Manipulated electromagnetic
losses by integrating chemically heterogeneous components
in Fe-based core/shell architecture. J Appl Phys 113(8):
084312
Huang J, Zhong X et al (2012) Improving the magnetic resonance
imaging contrast and detection methods with engineered
magnetic nanoparticles. Theranostics 2(1):86
Hufschmid R, Arami H et al (2015) Synthesis of phase-pure and
monodisperse iron oxide nanoparticles by thermal decompo-
sition. Nanoscale 7(25):11142–11154
Huh Y-M, Jun Y-w et al (2005) In vivo magnetic resonance
detection of cancer by using multifunctional magnetic
nanocrystals. J Am Chem Soc 127(35):12387–12391
Hurley KR, Ring HL et al (2016) Predictable heating and positive
MRI contrast from a mesoporous silica-coated iron oxide
nanoparticle. In: Molecular pharmaceutics
Hyeon T, Lee SS et al (2001) Synthesis of highly crystalline
and monodisperse maghemite nanocrystallites without a
size-selection process. J Am Chem Soc 123(51):12798–
12801
Iqbal MZ, Ma X et al (2015) Silica-coated super-paramagnetic
iron oxide nanoparticles (SPIONPs): a new type contrast
agent of T 1 magnetic resonance imaging (MRI). J Mater
Chem B 3(26):5172–5181
Jae-Hyun L, Yong-Min H et al (2007) Artificially engineered
magnetic nanoparticles for ultra-sensitive molecular imaging.
Nat Med 13(1):95
Jagadale TC, Takale SP et al (2008) N-doped TiO2 nanoparticle
based visible light photocatalyst by modified peroxide sol–
gel method. J Phys Chem C 112(37):14595–14602
Jain S, Rathi VV et al (2012) Folate-decorated PLGA nanoparti-
cles as a rationally designed vehicle for the oral delivery of
insulin. Nanomedicine 7(9):1311–1337
Jana NR, Chen Y et al (2004) Size-and shape-controlled magnetic
(Cr, Mn, Fe, Co, Ni) oxide nanocrystals via a simple and
general approach. Chem Mater 16(20):3931–3935
Jang J t, Nah H et al (2009) Critical enhancements of MRI contrast
and hyperthermic effects by dopant-controlled magnetic
nanoparticles. Angew Chem 121(7):1260–1264
Jennings LE, Long NJ (2009) ‘Two is b e tte r t han o n e’—probes for
dual-modality molecular imaging. Chem Commun (24):
3511–3524
Jing, X.-h., L. Yang, et al. (2008). In vivo MR imaging track-
ing of magnetic iron oxide nanoparticle labeled,
engineered, autologous bone marrow mesenchymal stem
cells following intra-articular injection. Joint Bone Spine
75(4): 432-438.
Jitianu A, Raileanu M et al (2006) Fe3O4–SiO2 nanocomposites
obtained via alkoxide and colloidal route. J Sol-Gel Sci
Technol 40(2-3):317–323
Joshi HM, Lin YP et al (2009) Effects of shape and size of cobalt
ferrite nanostructures on their MRI contrast and thermal
activation. J Phys Chem C 113(41):17761–17767
366 Page 20 of 25 J Nanopart Res (2017) 19:366

Jun Y w, Lee JH et al (2008a) Chemical design of nanoparticle
probes for high-performance magnetic resonance imaging.
Angew Chem Int Ed 47(28):5122–5135
Jun YW, Seo JW et al (2008b) Nanoscaling laws of magnetic
nanoparticles and their applicabilities in biomedical sciences.
Acc Chem Res 41(2):179–189
Kahn E, Tessier C et al (2002) Distribution of injected MRI
contrast agents in mouse livers studied by confocal and
SIMS microscopy. Anal Quant Cytol Histol 24(5):295–302
Kamaly N, Miller AD (2010) Paramagnetic liposome nanoparti-
cles for cellular and tumour imaging. Int J Mol Sci 11(4):
1759–1776
Kandpal ND, Sah N et al (2014) Co-precipitation method of
synthesis and characterization of iron oxide nanoparticles. J
Sci Ind Res 73:87–90
Kasche V, de Boer M et al (2003) Direct observation of
intraparticle equilibration and the rate-limiting step in
adsorption of proteins in chromatographic adsorbents
with confocal laser scanning microscopy. J Chromatogr
B 790(1):115–129
Kato T, Yashiro Tet al (2003) Evidence that exogenous substances
can be phagocytized by alveolar epithelial cells and
transported into blood capillaries. Cell Tissue Res 311(1):
47–51
Kim BH, Lee N et al (2011) Large-scale synthesis of uniform and
extremely small-sized iron oxide nanoparticles for high-
resolution T 1 magnetic resonance imaging contrast agents.
J Am Chem Soc 133(32):12624–12631
Kim D, Lee N et al (2008) Synthesis of uniform ferrimag-
netic magnetite nanocubes. J Am Chem Soc 131(2):
454–455
Kim J, Kim HS et al (2008) Multifunctional uniform nanoparticles
composed of a magnetite nanocrystal core and a mesoporous
silica shell for magnetic resonance and fluorescence imaging
and for drug delivery. Angew Chem Int Ed 47(44):8438–
8441
Kim J, Piao Y et al (2009) Multifunctional nanostructured mate-
rials for multimodal imaging, and simultaneous imaging and
therapy. Chem Soc Rev 38(2):372–390
Kim SJ, Lewis B et al (2016) Superparamagnetic iron oxide
nanoparticles for direct labeling of stem cells and
in vivo MRI tracking. Contrast Media Mol Imaging
11(1):55–64
Kim YB, Bae KH et al (2009) Positive contrast visualization for
cellular magnetic resonance imaging using susceptibility-
weighted echo-time encoding. Magn Reson Imaging 27(5):
601–610
Kircher MF, Gambhir SS et al (2011) Noninvasive cell-tracking
methods. Nat Rev Clin Oncol 8(11):677–688
Kirchner C,Liedl Tet al (2005) Cytotoxicity of colloidal CdSe and
CdSe/ZnS nanoparticles. Nano Lett 5(2):331–338
Kluchova K, Zboril R et al (2009) Superparamagnetic maghemite
nanoparticles from solid-state synthesis—their
functionalization towards peroral MRI contrast agent and
magnetic carrier for trypsin immobilization. Biomaterials
30(15):2855–2863
Kolesnichenko, V., G. Goloverda, et al. (2016). Iron oxide nano-
particles with a variable size and an iron oxidation state for
imaging applications.
Kucheryavy P, He J et al (2013) Superparamagnetic iron oxide
nanoparticles with variable size and an iron oxidation
state as prospective imaging agents. Langmuir 29(2):
710–716
Kuo Y-T, Chen C-Y et al (2016) Development of bifunctional
gadolinium-labeled superparamagnetic nanoparticles (Gd-
MnMEIO) for in vivo MR imaging of the liver in an animal
model. PloS One 11(2):e0148695
Labarre D, Vauthier C et al (2005) Interactions of blood proteins
with poly (isobutylcyanoacrylate) nanoparticles decorated with
a polysaccharidic brush. Biomaterials 26(24):5075–5084
Lacroix L-M, Frey Huls N et al (2011) Stable single-crystalline
body centered cubic Fe nanoparticles. Nano Lett 11(4):1641–
1645
Lartigue L n, Hugounenq P et al (2012) Cooperative organization
in iron oxide multi-core nanoparticles potentiates their effi-
ciency as heating mediators and MRI contrast agents. ACS
Nano 6(12):10935–10949
Laurent S, Bridot J-L et al (2010) Magnetic iron oxide nanoparti-
cles for biomedical applications. Future 2(3):427–449
Laurent S, Forge D et al (2008) Magnetic iron oxide nanoparticles:
synthesis, stabilization, vectorization, physicochemical char-
acterizations, and biological applications. Chem Rev 108(6):
2064–2110
Lawaczeck R, Menzel M et al (2004) Superparamagnetic iron
oxide particles: contrast media for magnetic resonance imag-
ing. Appl Organomet Chem 18(10):506–513
Lawrence MJ, Rees GD (2000) Microemulsion-based media as
novel drug delivery systems. Adv Drug Deliv Rev 45(1):89–
121
Leao Andrade A, Domingos Fabris J et al (2015) Current status of
magnetite-based Core@Shell structures for diagnosis and
therapy in oncology short running title: biomedical applica-
tions of magnetite@shell structures. Curr Pharm Des 21(37):
5417–5433
Lee J-H, Huh Y-M et al (2007) Artificially engineered magnetic
nanoparticles for ultra-sensitive molecular imaging. Nat Med
13(1):95–99
Lee N, Choi Y et al (2012) Water-dispersible ferrimagnetic iron oxide
nanocubes with extremely high r 2 relaxivity for highly sensitive
in vivo MRI of tumors. Nano Lett 12(6):3127–3131
Lee N, Hyeon T(2012) Designed synthesis of uniformly sizediron
oxide nanoparticles for efficient magnetic resonance imaging
contrast agents. Chem Soc Rev 41(7):2575–2589
Lee N, Kim H et al (2011) Magnetosome-like ferrimagnetic iron
oxide nanocubes for highly sensitive MRI of single cells and
transplanted pancreatic islets. Proc Natl Acad Sci 108(7):
2662–2667
Leonardi S, Mirzaei A et al (2016) A comparison of the ethanol
sensing properties of α-iron oxide nanostructures prepared
via the sol–gel and electrospinning techniques.
Nanotechnology 27(7):075502
Li L, Jiang Wet al (2013) Superparamagnetic iron oxide nanopar-
ticles as MRI contrast agents for non-invasive stem cell
labeling and tracking. Theranostics 3(8):595–615
Li N, Xia T et al (2008) The role of oxidative stress in ambient
particulate matter-induced lung diseases and its implications
in the toxicity of engineered nanoparticles. Free Radic Biol
Med 44(9):1689–1699
Li YF, Chen C (2011) Fate and toxicity of metallic and metal-
containing nanoparticles for biomedical applications. Small
7(21):2965–2980
JNanopartRes (2017) 19:366 Page 21 of 25 366

Li Z, Tan B et al (2008) Direct coprecipitation route to monodis-
perse dual-functionalized magnetic iron oxide nanocrystals
without size selection. Small 4(2):231–239
Lindman S, Lynch I et al (2007) Systematic investigation of the
thermodynamics of HSA adsorption to N-iso-
propylacrylamide/N-tert-butylacrylamide copolymer nano-
particles. Effects of particle size and hydrophobicity. Nano
Lett 7(4):914–920
Ling D, Hyeon T (2013) Chemical design of biocompatible iron
oxide nanoparticles for medical applications. Small 9(9-10):
1450–1466
Ling D, Lee N et al (2015) Chemical synthesis and assembly of
uniformly sized iron oxide nanoparticles for medical appli-
cations. Acc Chem Res 48(5):1276–1285
Liu G, Gao J et al (2013) Applications and potential toxicity of
magnetic iron oxide nanoparticles. Small 9(9-10):1533–1545
Liu G, Xie J et al (2011) N-alkyl-PEI-functionalized iron oxide
nanoclusters for efficient siRNA delivery. Small 7(19):2742–
2749
Liu H, Chi D (2016) Synthesis of iron sulfide and iron oxide
nanocrystal thin films for green energy applications.
Procedia Eng 141:32–37
Liu W, Ma J et al (2016) Micron-size superparamagnetic iron-
oxides watercress with unique MRI properties. Mater Chem
Phys 170:123–128
Long GJ, Grandjean F (2013) Mössbauer spectroscopy applied to
inorganic chemistry. Media, Springer Science & Business
Lynch I (2007) Are there generic mechanisms governing interac-
tions between nanoparticles and cells? Epitope mapping the
outer layer of the protein–material interface. Physica A:
Statistical Mechanics and its Applications 373:511–520
Lynch I, Dawson KA (2008) Protein-nanoparticle interactions.
Nano Today 3(1):40–47
Magnitsky S, Zhang J et al (2017) Positive contrast from cells
labeled with iron oxide nanoparticles: quantitation of imag-
ing data. Magn Reson Med 78(5):1900–1910
Mailänder V, Lorenz MR et al (2008) Carboxylated
superparamagnetic iron oxide particles label cells intracellu-
larly without transfection agents. Mol Imaging Biol 10(3):
138–146
Mao B, Kang Z et al (2006) Synthesis of magnetite octahedrons
from iron powders through a mild hydrothermal method.
Mater Res Bull 41(12):2226–2231
Markides H, Rotherham M et al (2012) Biocompatibility and
toxicity of magnetic nanoparticles in regenerative medicine.
J Nanomater 2012:13
Masthoff I-C, Kraken M et al (2016) Study of the growth of
hydrophilic iron oxide nanoparticles obtained via the non-
aqueous sol–gel method. J Sol-Gel Sci Technol 77(3):553–
564
Matijevic E, Borkovec M (2012) Surface and colloid science.
Springer US.
Mazuel F, Espinosa A et al (2016) Massive intracellular biodeg-
radation of iron oxide nanoparticles evidenced magnetically
at single-endosome and tissue levels. ACS Nano 10(8):7627–
7638
McDonagh BH, Singh G et al (2016) L-dopa-coated manganese
oxide nanoparticles as dual MRI contrast agents and drug-
delivery vehicles. Small 12(3):301–306
Møller P, Jacobsen NR et al (2010) Role of oxidative damage in
toxicity of particulates. Free Radic Res 44(1):1–46
Monopoli MP, Walczyk D et al (2011) Physical–chemical aspects
of protein corona: relevance to in vitro and in vivo biological
impacts of nanoparticles. J Am Chem Soc 133(8):2525–2534
Monteiro-Riviere N, Inman A et al (2009) Limitations and relative
utility of screening assays to assess engineered nanoparticle
toxicity ina human cell line. Toxicol Appl Pharmacol 234(2):
222–235
Mooney DJ, Vandenburgh H (2008) Cell delivery mechanisms for
tissue repair. Cell Stem Cell 2(3):205–213
Morris MC, Gros E et al (2007) A non-covalent peptide-based
carrier for in vivo delivery of DNA mimics. Nucleic Acids
Res 35(7):e49
Mou X, Ali Z et al (2015) Applications of magnetic nanoparticles
in targeted drug delivery system. J Nanosci Nanotechnol
15(1):54–62
Mulder WJ, Griffioen AW et al (2007) Magnetic and fluorescent
nanoparticles for multimodality imaging. Nanomedicine
2(3):307–324
Mulens, V., M. d. P. Morales, et al. (2013). Development of
magnetic nanoparticles for cancer gene therapy: a compre-
hensive review. ISRN Nanomaterials 2013.
Na HB, Song IC et al (2009) Inorganic nanoparticles for MRI
contrast agents. Adv Mater 21(21):2133–2148
Nachimuthu RK, Jeffery RD et al (2014) Investigation of cerium-
substituted europium iron garnets deposited by biased target ion
beam deposition. IEEE Trans Magn 50(12):1–7
Nagineni VS, Zhao S et al (2005) Microreactors for syngas con-
version to higher alkanes: characterization of sol–gel-encap-
sulated nanoscale Fe–Co catalysts in the microchannels. Ind
Eng Chem Res 44(15):5602–5607
Neamnark A, Suwantong O et al (2009) Aliphatic lipid substitu-
tion on 2 kDa polyethylenimine improves plasmid delivery
and transgene expression. Mol Pharm 6(6):1798–1815
Nel A, Xia T et al (2006) Toxic potential of materials at the
nanolevel. Science 311(5761):622–627
Nie Z, Petukhova A et al (2010) Properties and emerging applica-
tions of self-assembled structures made from inorganic nano-
particles. Nat Nanotechnol 5(1):15–25
Nitin N, LaConte L et al (2004) Functionalization and peptide-
based delivery of magnetic nanoparticles as an intracel-
lular MRI contrast agent. JBIC. J Biol Inorg Chem 9(6):
706–712
Nizameev, I., A. Mustafina, et al. (2017). High performance
magneto-fluorescent nanoparticles assembled from terbium
and gadolinium 1, 3-diketones.
Nyström AM, Fadeel B (2012) Safety assessment of
nanomaterials: implications for nanomedicine. J Control
Release 161(2):403–408
Oberdörster E (2004) Manufactured nanomaterials (fuller-
enes, C60) induce oxidative stress in the brain of juve-
nile largemouth bass. Environ Health Perspect 112(10):
1058
Oberdörster G, Oberdörster E et al (2005) Nanotoxicology: an
emerging discipline evolving from studies of ultrafine parti-
cles. Environ Health Perspect 113(7):823
Otsuka H, Nagasaki Y et al (2003) PEGylated nanoparticles for
biological and pharmaceutical applications. Adv Drug Deliv
Rev 55(3):403–419
Padmanabhan P, Kumar A et al (2016) Nanoparticles in practice
for molecular-imaging applications: an overview. In: Acta
biomaterialia
366 Page 22 of 25 J Nanopart Res (2017) 19:366

Palekar RU, Jallouk AP et al (2015) Molecular imaging of athero-
sclerosis with nanoparticle-based fluorinated MRI contrast
agents. Nanomedicine 10(11):1817–1832
Park J, Lee E et al (2005) One-nanometer-scale size-controlled
synthesis of monodisperse magnetic Iron oxide nanoparti-
cles. Angew Chem 117(19):2932–2937
Patel S, Hota G (2016) Iron oxide nanoparticle-immobilized PAN
nanofibers: synthesis and adsorption studies. RSC Adv
6(19):15402–15414
Pereira C, Pereira AM et al (2012) Superparamagnetic MFe2O4
(M= Fe, Co, Mn) nanoparticles: tuning the particle size and
magnetic properties through a novel one-step coprecipitation
route. Chem Mater 24(8):1496–1504
Petersen EJ, Nelson BC (2010) Mechanisms and measurements of
nanomaterial-induced oxidative damage to DNA. Anal
Bioanal Chem 398(2):613–650
Piao Y, Burns A et al (2008) Designed fabrication of silica-based
nanostructured particle systems for nanomedicine applica-
tions. Adv Funct Mater 18(23):3745–3758
Pisanic TR, Blackwell JD et al (2007) Nanotoxicity of iron oxide
nanoparticle internalization in growing neurons.Biomaterials
28(16):2572–2581
Poller WC, Ramberger E et al (2016) Uptake of citrate-coated iron
oxide nanoparticles into atherosclerotic lesions in mice oc-
curs via accelerated transcytosis through plaque endothelial
cells. Nano Res 9(11):3437–3452
Primc D, Belec B et al (2016) Synthesis of composite nanoparti-
cles using co-precipitation of a magnetic iron-oxide shell
onto core nanoparticles. J Nanopart Res 18(3):1–13
Rabias I, Fardis M et al (2008) No aging phenomena in ferrofluids:
the influence of coating on interparticle interactions of
maghemite nanoparticles. ACS Nano 2(5):977–983
Rabias I, Fardis M et al (2015) Novel synthesis of ultra-small
dextran coated maghemite nanoparticles for MRI and CT
contrast agents via a low temperature co-precipitation reaction.
J Nanosci Nanotechnol 15(1):205–210
Ramniceanu G, Doan B-T et al (2016) Delayed hepatic uptake of
multi-phosphonic acid poly (ethylene glycol) coated iron
oxide measured by real-time magnetic resonance imaging.
RSC Adv 6(68):63788–63800
Reddy LH, Arias JL et al (2012) Magnetic nanoparticles: design
and characterization, toxicity and biocompatibility, pharma-
ceutical and biomedical applications. Chem Rev 112(11):
5818–5878
Remya N, Syama S et al (2016) Toxicity, toxicokinetics and
biodistribution of dextran stabilized iron oxide nanopar-
ticles for biomedical applications. Int J Pharm 511(1):
586–598
Riaz S, Ashraf R et al (2014) Microwave assisted iron oxide
nanoparticles—structural and magnetic properties. IEEE
Trans Magn 50(8):1–4
Richard S, Eder V et al (2016) USPIO size control through
microwave nonaqueous sol-gel method for neoangiogenesis
T2 MRI contrast agent. Nanomedicine 11(21):2769–2779
Rivera Gil P, Oberdörster G n et al (2010) Correlating physico-
chemical with toxicological properties of nanoparticles: the
present and the future. Acs Nano 4(10):5527–5531
Roca A, Morales M et al (2006) Structural and magnetic properties
of uniform magnetite nanoparticles prepared by high temper-
ature decomposition of organic precursors. Nanotechnology
17(11):2783
Roca AG, Marco JF et al (2007) Effect of nature and particle size
on properties of uniform magnetite and maghemite nanopar-
ticles. J Phys Chem C 111(50):18577–18584
Rozanova N, Zhang JZ (2013) Metal and magnetic nanostructures
for cancer diagnosis and therapy. Reviews in. Nanosci
Nanotechnol 2(1):29–41
Rubio-Navarro A, Carril M et al (2016) CD163-macrophages are
involved in rhabdomyolysis-induced kidney injury and may
be detected by MRI with targeted gold-coated iron oxide
nanoparticles. Theranostics 6(6):896
Saeidian H, Moghaddam FM et al (2009) Superabsorbent polymer
as nanoreactors for preparation of hematite nanoparticles and
application of the prepared nanocatalyst for the Friedel-Crafts
acylation. J Braz Chem Soc 20(3):466–471
Safontseva NY, Nikiforov IY (2001) On the shape of iron K
absorption edges for monoferrites with a Me (Mg, Mn,
Ni, Zn) Fe 2 O 4 spinel structure. Phys Solid State 43(1):
61–64
Salvador-Morales C, Flahaut E et al (2006) Complement activa-
tion and protein adsorption by carbon nanotubes. Mol
Immunol 43(3):193–201
Santra S, Tapec R et al (2001) Synthesis and characterization of
silica-coated iron oxide nanoparticles in microemulsion: the
effect of nonionic surfactants. Langmuir 17(10):2900–2906
Sathya A, Guardia P et al (2016) Co x Fe3–x O4 nanocubes for
theranostic applications: effect of cobalt content and particle
size. Chem Mater 28(6):1769–1780
Sayes CM, Gobin AM et al (2005) Nano-C 60 cytotoxicity is due
to lipid peroxidation. Biomaterials 26(36):7587–7595
Schäfer R, Kehlbach R et al (2007) Transferrin receptor up-
regulation: in vitro labeling of rat mesenchymal stem cells
with superparamagnetic iron oxide. Radiology 244(2):
514–523
Shabestari Khiabani S, Farshbaf M et al (2016) Magnetic nano-
particles: preparation methods, applications in cancer diag-
nosis and cancer therapy. Artif Cells Nanomed Biotechnol
45(1):6–17
Sharifi S, Behzadi S et al (2012) Toxicity of nanomaterials. Chem
Soc Rev 41(6):2323–2343
Sheng-Nan S, Chao W et al (2014) Magnetic iron oxide nanopar-
ticles: synthesis and surface coating techniques for biomed-
ical applications. Chin Phys B 23(3):037503
Shin J, Anisur RM et al (2009) Hollow manganese oxide nano-
particles as multifunctional agents for magnetic resonance
imaging and drug delivery. Angew Chem Int Ed 48(2):321–
324
Shin T-H, Choi Y et al (2015) Recent advances in magnetic
nanoparticle-based multi-modal imaging. Chem Soc Rev
44(14):4501–4516
Simberg D, Park J-H et al (2009) Differential proteomics analysis
of the surface heterogeneity of dextran iron oxide nanoparti-
cles and the implications for their in vivo clearance.
Biomaterials 30(23):3926–3933
Simeonidis K, Mourdikoudis S et al (2007) Controlled synthesis
and phase characterization of Fe-based nanoparticles obtain-
ed by thermal decomposition. J Magn Magn Mater 316(2):
e1–e4
Smolensky ED, Park H-YE et al (2013) Scaling laws at the
nanosize: the effect of particle size and shape on the magne-
tism and relaxivity of iron oxide nanoparticle contrast agents.
J Mater Chem B 1(22):2818–2828
JNanopartRes (2017) 19:366 Page 23 of 25 366

Soenen SJ, Brisson AR et al (2009) Addressing the problem of
cationic lipid-mediated toxicity: the magnetoliposome mod-
el. Biomaterials 30(22):3691–3701
Soenen SJ, De Cuyper M (2009) Assessing cytotoxicity of (iron
oxide-based) nanoparticles: an overview of different methods
exemplified with cationic magnetoliposomes. Contrast
Media Mol Imaging 4(5):207–219
Soenen SJ, Himmelreich U et al (2011) Cytotoxic effects of iron
oxide nanoparticles and implications for safety in cell label-
ling. Biomaterials 32(1):195–205
Soenen SJ, Illyes E et al (2009) The role of nanoparticle
concentration-dependent induction of cellular stress in the
internalization of non-toxic cationic magnetoliposomes.
Biomaterials 30(36):6803–6813
Sohn O-J, Kim C-K et al (2008) Immobilization of glucose oxi-
dase and lactate dehydrogenase onto magnetic nanoparticles
for bioprocess monitoring system. Biotechnol Bioprocess
Eng 13(6):716–723
Sood A, Arora V et al (2016) Ascorbic acid-mediated synthesis
and characterisation of iron oxide/gold core–shell nanoparti-
cles. J Exp Nanosci 11(5):370–382
Sood A, Arora V et al (2017) Multifunctional gold coated iron
oxide core-shell nanoparticles stabilized using thiolated so-
dium alginate for biomedical applications. Mater Sci Eng C
80:274–281
Souto EB, Müller RH (2010) Lipid nanoparticles: effect on bio-
availability and pharmacokinetic changes. Springer, Drug
delivery, pp 115–141
Stephen ZR, Kievit FM et al (2011) Magnetite nanoparticles for
medical MR imaging. Mater Today 14(7):330–338
Sun DH, Trindade MC et al (2003) Human serum opsonization of
orthopedic biomaterial particles: protein-binding and
monocyte/macrophage activation in vitro. J Biomed Mater
Res A 65(2):290–298
Sun S, Zeng H (2002) Size-controlled synthesis of magnetite
nanoparticles. J Am Chem Soc 124(28):8204–8205
Sun S, Zeng H et al (2004) Monodisperse mfe2o4 (m= fe, co, mn)
nanoparticles. J Am Chem Soc 126(1):273–279
Szpak A, Fiejdasz S et al (2014) T1–T2 Dual-modal MRI contrast
agents based on superparamagnetic iron oxide nanoparticles
with surface attached gadolinium complexes. J Nanopart Res
16(11):1–11
Takami S, Sato T et al (2007) Hydrothermal synthesis of surface-
modified iron oxide nanoparticles. Mater Lett 61(26):4769–
4772
Tang Y, Chen Q (2007) A simple and practical method for the
preparation of magnetite nanowires. Chem Lett 36(7):840–
841
Tarin C, Carril M et al (2015) Targeted gold-coated iron oxide
nanoparticles for CD163 detection in atherosclerosis by MRI.
Scientific reports 5
Tartaj P, González-Carreño T et al (2004) From hollow to dense
spheres: control of dipolar interactions by tailoring the archi-
tecture in colloidal aggregates of superparamagnetic iron
oxide nanocrystals. Adv Mater 16(6):529–533
Tartaj P, Serna CJ (2002) Microemulsion-assisted synthesis of
tunable superparamagnetic composites. Chem Mater
14(10):4396–4402
Tassa C, Shaw SY et al (2011) Dextran-coated iron oxide nano-
particles: a versatile platform for targeted molecular imaging,
molecular diagnostics, and therapy. Acc Chem Res 44(10):
842–852
Tavakoli A, Sohrabi M et al (2007) A review of methods for
synthesis of nanostructured metals with emphasis on iron
compounds. Chem Pap 61(3):151–170
Tenzer S, Docter D et al (2013) Rapid formation of plasma protein
corona critically affects nanoparticle pathophysiology. Nat
Nanotechnol 8(10):772–781
Thomas R, Park I-K et al (2013)Magnetic iron oxide nanoparticles
for multimodal imaging and therapy of cancer. Int J Mol Sci
14(8):15910–15930
Thorek DL, Chen AK et al (2006) Superparamagnetic iron oxide
nanoparticle probes for molecular imaging. Ann Biomed Eng
34(1):23–38
Thu MS, Bryant LH et al (2012) Self-assembling nanocomplexes
by combining ferumoxytol, heparin and protamine for cell
tracking by magnetic resonance imaging. Nat Med 18(3):
463–467
Tombácz E, Turcu R et al (2015) Magnetic iron oxide nanoparticles:
recent trends in design and synthesis of magnetoresponsive
nanosystems. Biochem Biophys Res Commun 468(3):442–
453
Tong S, Hou S et al (2010) Coating optimization of
superparamagnetic iron oxide nanoparticles for high T2
relaxivity. Nano Lett 10(11):4607–4613
Trewyn BG, Slowing II et al (2007) Synthesis and
functionalization of a mesoporous silica nanoparticle based
on the sol–gel process and applications in controlled release.
Acc Chem Res 40(9):846–853
Tromsdorf UI, Bruns OT et al (2009) A highly effective, nontoxic
T 1 MR contrast agent based on ultrasmall PEGylated iron
oxide nanoparticles. Nano Lett 9(12):4434–4440
Umair M, Javed I et al (2016) Nanotoxicity of inert materials: the
case of gold, silver and iron. J Pharm Pharm Sci 19(2):161–
180
Unfried K, Albrecht C et al (2007) Cellular responses to nanopar-
ticles: target structures and mechanisms. Nanotoxicology
1(1):52–71
van Schooneveld MM, Vucic E et al (2008) Improved biocompat-
ibility and pharmacokinetics of silica nanoparticles by means
of a lipid coating: a multimodality investigation. Nano Lett
8(8):2517–2525
Walkey CD, Chan WC (2012) Understanding and controlling the
interaction of nanomaterials with proteins in a physiological
environment. Chem Soc Rev 41(7):2780–2799
Wang W, Pacheco V et al (2012a) Size and compositional effects
on contrast efficiency of functionalized superparamagnetic
nanoparticles at ultralow and ultrahigh magnetic fields. J
Phys Chem C 116(33):17880–17884
Wang H, Shrestha TB et al (2012b) Magnetic-Fe/Fe3O4-nanopar-
ticle-bound SN38 as carboxylesterase-cleavable prodrug for
the delivery to tumors within monocytes/macrophages.
Beilstein J Nanotechnol 3:444
Wang L, Tang W et al (2014) Improving detection specificity of
iron oxide nanoparticles (IONPs) using the SWIFT sequence
with long T 2 suppression. Magn Reson Imaging 32(6):671–
678
Wang Q, Shen M et al (2015) Low toxicity and long circulation
time of polyampholyte-coated magnetic nanoparticles for
blood pool contrast agents. Sci Rep 5:7774
366 Page 24 of 25 J Nanopart Res (2017) 19:366

Wang Y-XJ, Hussain SM et al (2001) Superparamagnetic iron
oxide contrast agents: physicochemical characteristics and
applications in MR imaging. Eur Radiol 11(11):2319–2331
Wang, Y., C. Xu, et al. (2013). Commercial nanoparticles for stem
cell labeling and.
Warheit DB, Laurence BR et al (2004) Comparative pulmonary
toxicity assessment of single-wall carbon nanotubes in rats.
Toxicol Sci 77(1):117–125
Wei W, Quanguo H et al (2007) Preparation and characterization
of magnetite Fe3O4 nanopowders. Rare Metal Mater Eng 36:
238–243
Weissleder R, Lee H (2017) et al. Magnetic nanoparticles, Google
Patents
Wetterskog E, Agthe M et al (2016) Precise control over shape and
size of iron oxide nanocrystals suitable for assembly into
ordered particle arrays. In: Science and Technology of
Advanced Materials
William WY, Chang E et al (2006) Aqueous dispersion of mono-
disperse magnetic iron oxide nanocrystals through phase
transfer. Nanotechnology 17(17):4483
Woo K, Hong J et al (2004) Easy synthesis and magnetic proper-
ties of iron oxide nanoparticles. Chem Mater 16(14):2814–
2818
Wu J, Ding T et al (2013) Neurotoxic potential of iron oxide
nanoparticles in the rat brain striatum and hippocampus.
Neurotoxicology 34:243–253
Wu S, Sun A et al (2011) Fe 3 O 4 magnetic nanoparticles
synthesis from tailings by ultrasonic chemical co-precipita-
tion. Mater Lett 65(12):1882–1884
Wu W, Wu Z et al (2015a) Recent progress on magnetic iron oxide
nanoparticles: synthesis, surface functional strategies and
biomedical applications. Sci Technol Adv Mater 16(2):
023501
Wu M, Zhang D et al (2015b) Nanocluster of superparamagnetic
iron oxide nanoparticles coated with poly (dopamine) for
magnetic field-targeting, highly sensitive MRI and
photothermal cancer therapy. Nanotechnology 26(11):
115102
Xia T, Kovochich M et al (2006) Comparison of the abilities of
ambient and manufactured nanoparticles to induce cellular
toxicity according to an oxidative stress paradigm. Nano Lett
6(8):1794–1807
Xu C, Sun S (2013) New forms of superparamagnetic nanoparti-
cles for biomedical applications. Adv Drug Deliv Rev 65(5):
732–743
Xu C, Teja AS (2008) Continuous hydrothermal synthesis of iron
oxide and PVA-protected iron oxide nanoparticles. J
Supercrit Fluids 44(1):85–91
Xu J, Yang H et al (2007) Preparation and magnetic prop-
erties of magnetite nanoparticles by sol–gel method. J
Magn Magn Mater 309(2):307–311
Yalcin S, Khodadust R et al (2015) Synthesis and characterization
of polyhydroxybutyrate coated magnetic nanoparticles: tox-
icity analyses on different cell lines. Synthesis and Reactivity
in Inorganic, Metal-Organic, and Nano-Metal. Chemistry
45(5):700–708
Yang H, Zhuang Y etal (2011) Targeted dual-contrast T1- and T 2-
weighted magnetic resonance imaging of tumors using mul-
tifunctional gadolinium-labeled superparamagnetic iron ox-
ide nanoparticles. Biomaterials 32(20):4584–4593
Yang M, Gao L et al (2015a) Characterization of Fe 3 O 4/
SiO 2/Gd 2 O (CO 3) 2 core/shell/shell nanoparticles as
T1 and T2 dual mode MRI contrast agent. Talanta 131:
661–665
Yang L, Zhou Z et al (2015b) Europium-engineered iron oxide
nanocubes with high T1 and T2 contrast abilities for MRI in
living subjects. Nanoscale 7(15):6843–6850
Yang X, Gondikas AP et al (2011) Mechanism of silver nanopar-
ticle toxicity is dependent on dissolved silver and surface
coating in Caenorhabditis elegans. Environ Sci Technol
46(2):1119–1127
Yazdani F, Fattahi B et al (2016) Synthesis of functionalized
magnetite nanoparticles to use as liver targeting MRI contrast
agent. J Magn Magn Mater 406:207–211
Yen SK, Padmanabhan P et al (2013) Multifunctional iron oxide
nanoparticles for diagnostics, therapy and macromolecule
delivery. Theranostics 3(12):986
Yoon TJ, Lee H et al (2011) Highly magnetic core–shell
nanoparticles with a unique magnetization mechanism.
Angew Chem Int Ed 50(20):4663–4666
Yu L, Yang X et al (2011) Preparation and magnetic properties of
doped Ni-Fe/Fe3O4 nanocomposite. Mater Manuf Process
26(11):1383–1387
Zelina P, Jašek O et al (2012) Versatile low-pressure plasma-
enhanced process for synthesis of iron and iron-based mag-
netic nanopowders. World Journal of. Engineering 9(2):161–
166
Zeng D-W, Xiao R et al (2016) Liquid foam assisted sol–gel
synthesis of iron oxides for hydrogen storage via chemical
looping. Int J Hydrog Energy 41(32):13923–13933
Zeng L, Ren W et al (2012) Ultrasmall water-soluble metal-iron
oxide nanoparticles as T 1-weighted contrast agents for mag-
netic resonance imaging. Phys Chem Chem Phys 14(8):
2631–2636
Zhang H, Malik V et al (2017) Synthesis and characterization of
Gd-doped magnetite nanoparticles. J Magn Magn Mater 423:
386–394
Zhang J, Ring HL et al (2016) Quantification and biodistribution
of iron oxide nanoparticles in the primary clearance organs of
mice using T1 contrast for heating. Magn Reson Med 78(2):
702–712
Zhao X, Wang J et al (2010a) Removal of fluoride from aqueous
media by Fe 3 O 4@ Al (OH) 3 magnetic nanoparticles. J
Hazard Mater 173(1):102–109
Zhao M-X, Xia Q et al (2010b) Synthesis, biocompatibility
and cell labeling of L-arginine-functional β-cyclodex-
trin-modified quantum dot probes. Biomaterials 31(15):
4401–4408
Zhao Z, Zhou Z et al (2013) Octapod iron oxide nanoparticles as
high-performance T2 contrast agents for magnetic resonance
imaging. Nat Commun 4:2266
Zhou Z, Wang L et al (2013) Engineered iron-oxide-based nano-
particles as enhanced T 1 contrast agents for efficient tumor
imaging. ACS nano 7(4):3287–3296
Zou J, Ostrovsky S et al (2016) Efficient penetration of ceric
ammonium nitrate oxidant-stabilized gamma-maghemite
nanoparticles through the oval and round windows into the
rat inner ear as demonstrated by MRI. In: Journal of
Biomedical Materials Research Part B: Applied Biomaterials
JNanopartRes (2017) 19:366 Page 25 of 25 366