Chitosan nanoparticle based delivery systems for sustainable agriculture

Full text

International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
Contents
lists
available
at
ScienceDirect
International
Journal
of
Biological
Macromolecules
j
ourna
l
ho
me
pa
g
e:
www.elsevier.com/locate/ijbiomac
Review
Chitosan
nanoparticle
based
delivery
systems
for
sustainable
agriculture
Prem
Lal
Kashyapa,b,∗,
Xu
Xiangb,
Patricia
Heidenb
aICAR-National
Bureau
of
Agriculturally
Important
Microorganisms
(NBAIM),
Mau,
Uttar
Pradesh
275101,
India
bMichigan
Technological
University
(MTU),
Houghton,
MI
49931,
USA
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
18
October
2014
Received
in
revised
form
3
February
2015
Accepted
16
February
2015
Available
online
5
March
2015
Keywords:
Chitosan
Encapsulation
Agriculture
Plant
protection
Controlled
release
Nanoparticles
a
b
s
t
r
a
c
t
Development
of
technologies
that
improve
food
productivity
without
any
adverse
impact
on
the
ecosys-
tem
is
the
need
of
hour.
In
this
context,
development
of
controlled
delivery
systems
for
slow
and
sustained
release
of
agrochemicals
or
genetic
materials
is
crucial.
Chitosan
has
emerged
as
a
valuable
carrier
for
controlled
delivery
of
agrochemicals
and
genetic
materials
because
of
its
proven
biocompatibility,
biodegradability,
non-toxicity,
and
adsorption
abilities.
The
major
advantages
of
encapsulating
agro-
chemicals
and
genetic
material
in
a
chitosan
matrix
include
its
ability
to
function
as
a
protective
reservoir
for
the
active
ingredients,
protecting
the
ingredients
from
the
surrounding
environment
while
they
are
in
the
chitosan
domain,
and
then
controlling
their
release,
allowing
them
to
serve
as
efficient
gene
deliv-
ery
systems
for
plant
transformation
or
controlled
release
of
pesticides.
Despite
the
great
progress
in
the
use
of
chitosan
in
the
area
of
medical
and
pharmaceutical
sciences,
there
is
still
a
wide
knowledge
gap
regarding
the
potential
application
of
chitosan
for
encapsulation
of
active
ingredients
in
agriculture.
Hence,
the
present
article
describes
the
current
status
of
chitosan
nanoparticle-based
delivery
systems
in
agriculture,
and
to
highlight
challenges
that
need
to
be
overcome.
©
2015
Elsevier
B.V.
All
rights
reserved.
Contents
1.
Introduction
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37
1.1.
Chitosan
in
crop
production
and
protection.
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1.2.
Chitosan
as
a
promising
delivery
system
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41
1.3.
Strategies
for
production
of
chitosan
nanoparticles.
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41
1.4.
Emulsion
cross-linking.
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1.5.
Emulsion-droplet
coalescence
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44
1.6.
Ionotropic
gelation
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44
1.7.
Precipitation.
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44
1.8.
Reverse
micelles
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1.9.
Seiving
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1.10.
Spray
drying
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45
1.11.
Strategies
for
loading
active
ingredient
into
chitosan
nanoparticles
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45
1.12.
Release
kinetics
of
active
ingredients
from
chitosan
nanoparticles
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45
2.
Applications
of
chitosan
nanoparticles
as
a
delivery
system
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46
2.1.
Pesticide
delivery
for
crop
protection
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46
2.2.
Fertilizer
delivery
for
balanced
and
sustained
nutrition
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46
2.3.
Herbicide
delivery
for
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eradication
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47
2.4.
Micronutrient
delivery
for
crop
growth
promotion
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47
∗Corresponding
author
at:
ICAR-National
Bureau
of
Agriculturally
Important
Microorganisms
(NBAIM),
Mau,
Uttar
Pradesh
275103.
E-mail
address:
plkashyap@gmail.com
(P.L.
Kashyap).
http://dx.doi.org/10.1016/j.ijbiomac.2015.02.039
0141-8130/©
2015
Elsevier
B.V.
All
rights
reserved.

P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
37
2.5.
Soil
health
improvement
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47
2.6.
Delivery
of
genetic
material
for
plant
transformation
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47
3.
Conclusions
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48
References
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48
1.
Introduction
The
biggest
challenge
faced
by
agricultural
researchers
is
to
produce
sufficient
quantity
and
quality
of
food
to
feed
the
ever
increasing
global
population
without
degrading
the
soil
health
and
agro-ecosystem.
It
has
been
estimated
that
global
food
production
must
increase
by
70–100%
by
2050
to
meet
the
demand
of
the
growing
population
explosion
[1].
Agricultural
production
contin-
ues
to
be
challenged
by
a
large
number
of
insect
pests,
diseases,
and
weeds
accounting
for
40%
losses
to
the
tune
of
US
$2000
bil-
lion
per
year
[2].
To
manage
these
losses
and
enhance
productivity,
farmers
are
making
excessive
and
indiscriminate
use
of
agrochem-
icals
which
leads
to
deterioration
of
soil
health,
degradation
of
agro-ecosystems,
residue
problems,
environmental
pollution
and
pesticide
resistance
in
insects
and
pathogens.
Hence,
there
is
an
urgent
need
to
change
the
manner
in
which
we
use
agrochem-
icals.
Changes
can
include
(i)
judicious
deployment
of
pesticide
and
fertilizer,
(ii)
rapid
and
precise
detection
of
pathogens
and
pests,
as
well
as
pesticides
and
nutrient
levels,
and
(iii)
promoting
soil
health
by
agrochemical
degradation.
In
this
context,
nano-
technology
has
emerged
as
a
technological
advancement
that
can
transform
agriculture
and
allied
sectors
by
providing
with
novel
tools
for
the
molecular
management
of
biotic
and
abiotic
stresses,
rapid
disease
detection
and
enhancing
the
ability
of
plants
to
absorb
nutrients
or
pesticides
[3–5].
Besides
this,
nanobiotechnology
can
also
improve
our
understanding
of
crop
biology
and
thus
can
poten-
tially
enhance
crop
yields
or
their
nutritional
values.
Nanosensors
and
nano-based
smart
delivery
systems
are
some
of
the
nanotech-
nology
applications
that
are
currently
employed
in
the
agricultural
industry
to
aid
with
combating
crop
pathogens,
minimizing
nutri-
ent
losses
in
fertilization,
improving
crop
productivity
through
optimized
water
and
nutrient
management
as
well
as
to
enhance
the
efficiency
of
pesticides
at
lower
dosage
rates
[6,7].
Nanotech-
nology
derived
devices
are
also
being
explored
in
the
field
of
plant
breeding
and
genetic
transformation
[8,9].
Table
1
describes
some
of
the
advancements
made
in
the
field
of
agricultural
nano-
technology.
Among
all
these
advancements,
encapsulating
active
ingredients,
such
as
fertilizers,
herbicides,
fungicides,
insecticides,
and
micronutrients
in
controlled
release
matrices
is
one
of
the
most
promising
and
viable
options
for
tackling
current
challenges
in
the
area
of
agricultural
sustainability
and
food
security
in
the
face
of
climate
change.
It
has
been
shown
that
encapsulation
of
active
ingredients
in
nanoparticles
enhances
the
efficacy
of
chemical
ingredients,
reducing
their
volatilization,
and
decreasing
toxicity
and
environmental
contamination
[40].
Chitosan
has
emerged
as
one
of
the
most
promising
polymers
for
the
efficient
delivery
of
agrochemicals
and
micronutrients
in
nanoparticles
(Fig.
1;
Table
2).
The
enhanced
efficiency
and
effi-
cacy
of
nanoformulations
are
due
to
higher
surface
area,
induction
of
systemic
activity
due
to
smaller
particle
size
and
higher
mobility,
and
lower
toxicity
due
to
elimination
of
organic
solvents
in
com-
parison
to
conventionally
used
pesticides
and
their
formulations
[62,63].
Chitosan
nanoparticles
have
been
investigated
as
a
car-
rier
for
active
ingredient
delivery
for
various
applications
(Fig.
1)
owing
to
their
biocompatibility,
biodegradability,
high
perme-
ability,
cost-effectiveness,
non-toxicity
and
excellent
film
forming
ability
[64].
Over
the
past
three
decades,
various
procedures
like
cross-linking,
emulsion
formation,
coacervation,
precipitation
and
self-assembly,
etc.
have
been
employed
to
synthesize
chitosan
nanoparticles
[65,66].
Chitosan
has
also
known
for
its
broad
spec-
trum
antimicrobial
and
insecticidal
activities
[67,68].
Further,
it
is
biodegradable
giving
non-toxic
residues
with
its
rate
of
degrada-
tion
corresponding
to
molecular
mass
and
degree
of
deacetylation
[69,70].
However,
the
low
solubility
of
bulk
chitosan
in
aqueous
media
limits
its
wide
spectrum
activity
as
an
antimicrobial
agent.
Therefore,
various
strategies
have
been
employed
to
enhance
its
antifungal
potential
[41].
Chitosan
is
able
to
chelate
various
organic
and
inorganic
compounds,
making
it
well-suited
for
improving
the
stability,
solubility
and
biocidal
activity
of
chelated
fungicides
or
other
pesticides
[64].
For
example,
copper
(Cu)
compounds
are
well
known
for
their
antifungal
nature
and
have
been
used
with
chi-
tosan
for
antibacterial
and
antifungal
activities.
The
majority
of
the
research
on
chitosan
nanoparticles
in
agricultural
research
studied
their
biocidal
and
antagonistic
effects
on
bacteria
and
fungi,
and
gave
encouraging
results
[71–73].
Chitosan-based
nanocompos-
ite
films,
especially
silver-containing
ones,
showed
antimicrobial
activity
against
several
pathogens
[74],
but
some
effect
was
also
observed
with
chitosan
films
alone
[75].
Other
studies
investigated
the
use
of
chitosan–PVA
hydrogels
for
antimicrobial
and
food
pack-
aging
applications
[76–78].
The
combination
of
silver
nanoparticles
within
a
chitosan–PVA
polymeric
material
also
emerged
as
one
of
the
most
promising
candidates
for
new
antimicrobial
materials
[44].
Recently,
application
of
chitosan
particles
loaded
with
copper
has
been
reported
in
waste
water
treatment
[79,80].
Considering
the
growing
interest,
and
recent
advances,
in
chitosan-based
nano-
materials
in
medical
and
pharmacological
applications,
the
purpose
of
this
article
is
to
review
the
current
and
ongoing
research
and
developmental
efforts
into
chitosan
nanoparticles
as
a
delivery
sys-
tem,
with
particular
focus
on
describing
methods
that
would
be
suitable
for
promoting
crop
productivity.
1.1.
Chitosan
in
crop
production
and
protection
There
have
been
several
reports
describing
the
use
of
chitosan
for
biotic
and
abiotic
stress
management
in
agriculture
[73,81–85].
Table
3
lists
some
of
the
applications
of
chitosan
in
crop
pro-
duction
and
protection.
For
the
first
time,
Allan
and
Hadwiger
[130]
described
the
application
of
chitosan
as
an
antimicrobial
agent.
This
has
led
to
the
exploitation
of
its
antimicrobial
potential
in
various
sectors
of
agriculture.
Since
the
1980s,
the
study
of
chitosan
has
been
shift
from
a
general
sewage
treatment
agent
to
plant
growth
regulator,
soil
conditioner,
vegetables
and
fruits
antistaling
agent,
and
seed
coating
agent,
especially
in
the
crop
disease
management.
Several
studies
showed
that
chitosan
is
not
only
an
antimicrobial
agent
but
also
an
effective
elicitor
of
plant
systemic
acquired
resistance
to
pathogens
[73,82,84,131].
This
polymer
has
been
reported
to
be
the
enhancer
and
regulator
of
plant
growth,
development
and
yield
[85,132,133].
Chitosan
has
been
demonstrated
to
induce
plant
defences
in
tomato
[87,89],
cucumber
[97],
chilli
seeds
[102],
strawberry
fruits
[88]
and
rose
shrubs
[99].
Chitosan
can
activate
innate
immunity
by
stimulating
hydrogen
peroxide
(H2O2)
production
in
rice
[134,135],
induce
a
defense
response
by
nitric
oxide
(NO)
pathways
in
tobacco
[136,137],
promote
the
development
and
drought
resistance
of
coffee
[138],
support
the
synthesis
of
phytoalexin
[139],
impact
the
jasmonic
acid–ethylene
(JA/ET)
signaling
marker
in
oilseed
rape
[140],
cause
changes
in
protein
phosphorylation
[141],
activate
mitogen-activated
protein
kinases
(MAPKs)
[142]
and
trigger

38
P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
Table
1
Major
advancements
of
nanotechnology
in
agriculture.
Year
Advancement/application(s)
Institute(s)/company
Reference
2003
Soil
binder
product
based,
on
a
nano-siliica
component,
to
prevent
soil
runoff
and
allow
seeds
blended
into
the
product
to
germinate
US
based
company
(ETC
Group,
2004)
[10]
2005
Inorganic
Zn–Al
layered
double
hydroxide
(ZAL)
nanocomposite
based
controlled
release
of
herbicide
(2,4-dichlorophenoxyacetate
(2,4-D))
Advanced
Materials
Laboratory,
Institute
of
Advanced
Technology
(ITMA),
Malaysia
[11]
2006
Rapid
analysis
of
pirimicarb
residues
in
vegetables
using
molecularly
imprinted
polymers
(methacrylic
acid
with
carboxyl
functional
groups)
as
recognition
elements
University
of
Hong
Kong,
Hong
Kong
SAR,
China. [12]
2006
Nano-TiO2on
glassy
carbon
electrode
to
detect
parathion
(pesticide)
residue
in
vegetables
Wuhan
University,
Wuhan,
China;
Chinese
Academy
of
Sciences,
Beijing,
China
[13]
2006
Porous
hollow
silica
nanoparticles
(PHSNs)
for
controlled
delivery
system
for
water-soluble
pesticide
(validamycin)
Beijing
University
of
Chemical
Technology,
Beijing,
China
[14]
2006
Filters
coated
with
TiO2nanoparticles
for
the
photocatalytic
degradation
of
agrochemicals
in
contaminated
waters
University
of
Ulster,
UK [15]
2007
Pesticide
detection
with
aliposome-based
nano-biosensor
University
of
Crete,
GR
[16]
2007
Mesoporus
silica
nanoparticles
transporting
DNA
to
transform
plant
cells
Iowa
State
university,
US
[8]
2008
Primo
MAXX®,
nano
emulsions
as
plant
growth
regulator
and
stress
alleviator
Syngenta
Crop
Protection,
Greensboro,
NC
[17]
2008
Starch
nanoparticles
conjugated
with
fluorescent
material
transporting
DNA
to
transform
plant
cells
Université
de
Perpignan
via
Domitia,
Perpignan,
France;
Institute
for
Bioengineering
of
Catalonia,
Barcelone,
Spain
[18]
2008
Nanofibres
from
wheat
straw
and
soy
hulls
for
bio-nanocomposite
production
Canadian
Universities
and
Ontario
Ministry
of
Agriculture,
Food
and
Rural
Affairs,
CA
[19]
2009
PEG
coated
nanoparticles
loaded
with
garlic
essential
oil
for
control
of
storage
pests
(Tribolium
castaneum)
Huazhong
Agricultural
University,
Wuhan,
China
[20]
2009
Cadmium
telluride
quantum
dots
(CdTe
QDs)
to
detect
2,
4-dichlorophenoxyacetic
acid
(2,
4-D),
(herbicide)
Central
Food
Technological
Research
Institute,
Mysore,
India.
[21]
2009
Methyl
parathion
and
chlorpyrifos
residue
detection
using
nano
size
polyaniline
matrix
with
SWCNT,
single
stranded
DNA
and
enzyme
Institute
of
Animal
Reproduction
and
Food
Research,
Tuwima,
Poland
[22]
2009
Nano-sensor
for
early
detection
of
grain
spoilage
during
storage
University
of
Manitoba,
Winnipeg
[23]
2009
Pesticide
detection
using
gold
nanoparticles
based
dipstick
competitive
immuno-assay
Central
Food
Technological
Research
Institute,
Mysore,
India.
[24]
2009
Fluorescence
silica
nanoparticles
in
combination
with
antibody
to
detect
Xanthomonas
axonopodis
pv.
Vesicatoria
in
solanaceaous
crops
MingDao
University,
Taiwan;
National
Chung-Hsing
University,
Taiwan
[25]
2010
Soil-enhancer
product,
based
on
a
nano-clay
component,
for
water
retention
and
release
Geohumus-Frankfurt,
DE
[7]
2010
Pesticide
detection
using
nano-Au/nafion
composite
in
vegetables
(cabbage,
spinach,
lettuce)
Beijing
University
of
Technology,
China
[26]
2010
Carbon
nanotube
(CNT)
conjugated
with
INF24
oligonucleotides
to
reduce
the
bean
rust
disease
severity
Universidad
de
Chile,
Chile
[27]
2010
Magnetic
carbon
coated
nanoparticles
as
smart
agrochemical
delivery
system
IFAPA,
Centro
Alameda
del
Obispo,
Área
de
Mejora
y
Biotecnología,
Córdoba,
Spain;
CSIC-Universidad
de
Zaragoza,
Spain;
CSIC,
Instituto
de
Agricultura
Sostenible,
Alameda
Córdoba,
Spain
[28]
2010
Polyhydroxybutyrate-co-hydroxyvalerate
microspheres
as
controlled
release
herbicide
delivery
system
for
atrazine
UNESP—Univ.
Estadual
Paulista,
Brazil;
UNICAMP,
Cidade
Universitária
Zeferino,
Brazil;
University
of
Sorocaba,
Sorocaba,
SP,
Brazil
[29]
2010
Pathogen
detection
(Tilletia
indica)
using
nano-gold
based
immunosensors
based
on
surface
plasmon
resonance
(SPR)
G.B
Pant
University
of
Agri.
&
Tech.,
Pantnagar,
India;
National
Physical
Laboratory,
New
Delhi,
India
[30]
2010
Pathogen
(Sclerotinia
sclerotiorum)
detection
based
on
electrochemical
sensor,
using
modified
gold
electrode
with
copper
nanoparticle
to
monitor
the
levels
of
salicylic
acid
in
oil
seeds
Huazhong
University
of
Science
and
Technology,
Hubei
China;
Chinese
Academy
of
Agricultural
Sciences-Key
Laboratory
for
Genetic
Improvement
of
Oil
Crops,
China
[31]
2011
Amino-functionalized
nanocomposite
with
tetra-ethylene-pent-amine
for
organochlorine
and
organophosphorus
pesticides
in
cabbage
Ningbo
Municipal
Center
for
Disease
Control
and
Prevention,
Zhejiang,
China.
[32]
2011
Optical
sensor
for
the
detection
of
pesticides
(Dipel,
Siven
85%
WP)
in
water
using
ZnCdSe
Quantum
dots
films
Universiti
Kebangsaan
Malaysia,
Malaysia
[33]
2012
Neem
oil
(Azadirachta
indica)
nanoemulsion
as
larvicidal
agent
VIT
University,
India
[34]
2012
Macronutrient
fertilizers
coated
with
zinc
oxide
nanoparticles
University
of
Adelaide,
AU
CSIRO
Land
and
Water,
AU
Kansas
State
University,
US
[35]
2012
Amphotericin
B
nanodisks
(AMB-NDs)
for
the
treatment
of
fungal
pathogens
in
chickpea
and
wheat
plants
Área
de
Mejora
y
Biotecnología,
Córdoba,
Spain
[36]
2013
Pheromone
nanogel
for
the
efficient
management
of
fruit-fly
Indian
Institute
of
Science
(IIS),
Bangalore,
India;
National
Bureau
of
Agriculturally
Important
Insects
(NBAII),
India
[37]
2013
1-Naphthylacetic
acid
silica
conjugated
nanospheres
for
control
release
and
as
a
plant
growth
regulator
China
Agricultural
University,
China
[38]
2014
Nanoformulation
based
on
chitosan/tripolyphosphate
nanoparticles
loaded
with
paraquat
herbicide
for
control
release
and
eco-friendly
weed
management
UNESP—Univ.
Estadual
Paulista,
Brazil;
UNICAMP,
Cidade
Universitária
Zeferino,
Brazil;
University
of
Sorocaba,
Sorocaba,
SP,
Brazil
and
Max
Rubner
Institut,
Karlsruhe,
Germany
[39]
2014
Poly(epsilon-caprolactone)
nanoparticles
containing
atrazine
herbicide
as
an
alternative
technique
to
control
weeds
and
reduce
damage
to
the
environment
UNESP—Univ.
Estadual
Paulista,
Brazil;
UNICAMP,
Cidade
Universitária
Zeferino,
Brazil;
[7]

P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
39
Fig.
1.
Strategies
for
the
production
of
chitosan
naoparticles
and
their
applications
as
a
delivery
system
in
agriculture.
Table
2
Some
examples
of
active
ingredients
encapsulated
in
chitosan-based
controlled
release
matrices
in
agriculture.
Matrices
Method
Active
ingredient
Characteristics
Reference(s)
Cu-chitosan
nanoparticles
Ionic
gelation
CuSO4Enhanced
antifungal
activity
against
Alternaria
alternate,
Macrophomina
phaseolina
and
Rhizoctonia
solani
[41]
!-Fe3O4-CS
nanocomposite
film
Cross-linking
!-Fe3O4Heavy
metals
monitoring
with
low
detection
limit
[42]
Chitosan
microspheres Emulsion
cross-linking
Urea
Controlled
release
of
the
urea
fertilizer
[43]
Chitosan–PVA
hydrogel
Cross-linking
Silver
nanoaprticles
Size
of
13
nm;
exhibits
good
antibacterial
activity
[44]
Alginate
reinforced
chitosan
and
starch
beads
Cross-linking
Imazaquin
(Herbicide)
Porous
spherical
beads
of
2.31
mm
size;
sustained
slow
release
of
active
material
[45]
Composite
gel
Cross-linking
Atrazine
(Herbicide)
and
imidacloprid
Sustained
release
of
active
material
in
water
for
572
h
for
atrazine
and
24
h
for
imidacloprid,
respectively
[46]
Chitosan
microspheres
Emulsion
cross-linking
Auxins
(Agrochemical)
Chitosan
microspheres
extended
action
of
auxin
release
(up
to
120
h)
[47]
Chitosan
microspheres
Cross-linking
Paraquat
(Herbicide)
Sustained
release
of
active
material
in
water
for
8
h
[48]
Chitosan–silver
nanoparticles
composite
micro-beads
Cross-linking
Silver
nanoparticles
Pesticide
removal
for
extended
periods
[49]
Chitosan-coated
NPK
compound
fertilizer
Urea,
calcium
phosphate
and
potassium
chloride
Size
of
78
nm;
controlled
release
of
the
NPK
fertilizer
[50]
Chitosan
hydrogels
Cross-linking
Potassium
nitrate
(KNO3)
and
Dihydrogen
ammonium
phosphate
[(NH4)2HPO4]
Hydrogel
in
the
form
of
circular
pads
with
2
mm
in
thickness
and
120
mm
in
diameter;
controlled
release
of
the
potassium
fertilizer;
enhanced
up
to
25%
water
retention
of
the
soil
[51]
Chitosan
microcapsules
Precipitation
3-Hydroxy-5-methylisoxazole
(Herbicide)
Size
of
5
"m;
sustained
release
of
active
material
in
water
for
80–160
h
[52]
Chitosan
gel
beads
(with
acetic
or
propionic
anhydride)
Cross-linking
Atrazine
(Herbicide)
and
urea
(Fertilizer)
Extended
release
period
of
atrazine
to
7
months;
chitosan-coated
urea
beads
extended
action
of
urea
release
(up
to
180
h)
[53]
Beauvericin–chitosan
nanoparticles
Ionic
gelation
Beauvericin
(Pesticidal
cyclodepsipeptide)
Improved
pesticidal
activity
against
groundnut
defoliator
Spodoptera
litura
[54]
Alginate–chitosan
microcrystals
Self-assembly
Imidacloprid
(Insecticide)
A
novel
photodegradable
insecticide;
controlled
and
sustained
release
of
midacloprid;
showed
toxicity
against
Martianus
dermestoides
adults
[55]
Chitosan
nanoparticles
+
chitosan
–
Dichlorprop
(Herbicide)
Enhanced
toxicity
to
fresh
water
green
algae
and
slow
release
of
Dichlorprop
[56]
Chitosan
microspheres
Coacervation–cross-linking
Brassinosteroids
(Hormones)
Controlled
delivery
of
brassinosteroids
with
biological
activity
as
agrochemicals
[57]
Chitosan
–
Dichlorprop
(Herbicide)
Controlled
and
slow
release
of
dichlorprop
[58]
Chitosan
nanoparticles
–
Hexavalent
chromium
(Metal)
Effective
agent
for
in
situ
subsurface
environment
remediation
[59]
N-(octadecanol-1-glycidyl
ether)-O-sulfate
chitosan
(NOSCS)
micelle
Reverse
micelle
Rotenone
(Insecticide)
Useful
as
a
prospective
carrier
for
control
released
agrochemical
[60]
Chitosan
–
1-Naphthylacetic
acid
(Hormone)
Controlled
and
slow
release
of
1-Naphthylacetic
acid
[61]
–,
Not
mentioned.

40
P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
Table
3
Principal
studies
reported
in
the
literature
involving
chitosan
use
for
plant
growth
promotion
and
protection
from
1984
to
2015.
Year
Plant/crop
Effect/impact
of
chitosan
application
Reference
1984
Pea
Antifungal
activity
against
Fusarium
solani
due
to
synthesis
and
elicitation
of
pisatin
phytoalexin
[86]
1992
Tomato
Enhanced
resistance
of
tomato
plants
to
the
crown
and
root
rot
pathogen
Fusarium
oxysporum
f.
sp.
radicis-lycopersici
[87]
1992
Strawberry
Antifungal
activity
against
postharvest
pathogens
[88]
1994
Tomato
Induction
of
systemic
resistance
to
Fusarium
crown
and
root
rot
[89]
1998
Celery
Reduction
in
the
incidence
and
severity
of
Fusarium
yellows
[90]
2001
Pepper
Enhanced
biomass
production
and
yield
by
decreasing
transpiration
and
water
use
by
26–43%
[91]
2001
Maize
Induction
in
endogenous
hormone
content,
alpha-amylase
activity
and
chlorophyll
content
in
seedling
leaves
[92]
2002
Mulberry
Enhancement
in
respiration
rate
of
germination
seeds,
root
vigor,
chlorophyll,
protein
content
and
peroxidase
in
seedlings
as
well
as
nitrate
reductase
and
amylase
activities
[93]
2002
Cucumber,
Chilli,
pumpkin,
and
cabbage
Increment
in
the
seed
germination
rate
[94]
2002
Peanut
Enhancement
in
the
energy
of
germination
and
germination
percentage
[95]
2002
Soybean
Enhancement
in
growth
and
yield
[96]
2003
Cucumber
Containment
of
gray
mold
infection
in
plants
caused
by
Botyrtis
cinerea
[97]
2003
Potato
Enhancement
in
yield
and
late
blight
resistance
by
Arbuscular
mycorrhizal
fungi
band
chitosan
sprays
[98]
2004
Rose
shrubs Enhanced
resistance
against
foliar
diseases [99]
2004
Date
palm
Antifungal
activity
against
Fusarium
oxysporum
f.
sp.
albedinis
and
elicitor
of
defence
reactions
[100]
2005
Maize
Increased
in
plant
vigor
[101]
2006
Chilli
Enhanced
resitance
against
Colletotrichum
sp.;
promote
of
seedling
growth
[102]
2006
Grapevine
Induction
of
plant
defence
system
against
gray
mold
and
downy
mildew
[103]
2007
Rice
(Oryza
sativa)
Induction
of
defence
response
against
Pyricularia
grisea
[104]
2007
Papaya
Antifungal
activity
against
anthracnose
and
improvement
in
quality
retention
of
papaya
during
storage
[105]
2008
Tobacco
Elicitation
of
callose
apposition
and
abscisic
acid
accumulation
in
response
to
Tobacco
necrosis
virus
attack
[106]
2008
Pearl
millet
Enhanced
seed
germination
and
seedling
vigor
[107]
2009
Maize
Increased
chilling
tolerance
of
maize
seedlings
and
induced
higher
activities
of
antioxidative
enzymes
[108]
2010
Pear
Elevated
defense-related
enzymes
activity
[109]
2010
Grape
Direct
antifungal
activity
against
Botrytis
bunch
rot
and
induction
of
defense-related
enzymes
activities
[110]
2010
Sweet
cherry
Maintained
quality
attributes
and
extended
the
postharvest
life
by
inducing
defense-related
enzymes
activities
[111]
2010
Mango
Combined
effects
of
postharvest
heat
treatment
and
chitosan
coating
on
quality
and
antimicrobial
properties
of
fresh
cut
mangoes
[112]
2011
Hypericum
perforatum
Produced
xanthone-rich
extracts
with
antifungal
activity
[113]
2011
Tomato
Accumulated
phosphatidic
acid
and
nitric
oxide
[114]
2011
Apricot
Direct
inhibition
activity
against
fruit
rot
[115]
2011
Radish
Promoted
the
uptake
of
nutrients,
nitrogen,
potassium
and
phosphorous,
decreased
cadmium
concentration
[116]
2011
Barley
Induced
stomatal
closure
[117]
2012
Okra
Foliar
application
of
chitosan
(100
ppm)
enhanced
growth
and
fruit
yield [118]
2012
Sycamore
Enhanced
the
production
of
H2O2and
nitric
oxide
[119]
2012
Rice
Sheath
blight
induced
activity
of
defense-related
enzymes
[120]
2013
Ajowan
(Carum
copticum)
Improvement
in
the
germination
and
growth
performance
of
ajowan
(Carum
copticum)
under
salt
stress
[121]
2013
Safflower
and
sunflower
Elevated
activity
of
antioxidant
enzymes
[122]
2013
Rice
Showed
positive
and
promising
effects
in
increasing
rice
yield
and
inhibiting
brown
backed
rice
plant-hoppers
[123]
2013
Watermelon
Direct
killing
effect
and
protection
from
fruit
blotch
disease
[124]
2013
Peach
Reduced
brown
rot
infection
and
enhanced
antioxidant
and
defense-related
enzymes
[125]
2013
Pine
Up-regulated
the
expression
level
of
defense-related
enzymes
and
Pitch
canker
[126]
2013
Camellia
Accumulated
H2O2,
defense-related
enzymes,
and
soluble
protein
and
Anthracnose
[127]
2013
Broccoli
Antimicrobial
coating
served
as
carriers
for
bioactive
compounds
[128]
2014
Tomato
Alternatives
fungicide
for
controlling
Fusarium
crown
and
root
rot
[129]
2015
Wheat
Potential
application
as
a
plant
growth
regulator
[85]
defense-related
gene
expression
[143].
Even
applied
on
plants
together
with
biological
control
agents,
chitosan
enhanced
the
efficacy
in
the
control
of
pathogens
[144,145].
Soil
amendment
with
chitosan
has
frequently
been
shown
to
control
Fusarium
wilts
[90,146,147]
and
gray
molds
[97,103]
in
a
number
of
crops.
It
is
interesting
to
note
that
these
studies
show
chitosan
to
be
fungistatic
against
both
biotrophic
and
necrotrophic
pathogens.
Besides
this,
another
one
of
the
most
important
bioactivity
of
chitosan
on
plants
is
stimulation
of
seed
germination
in
response
to
abiotic
stress.
In
peanut,
seed
coated
with
chitosan
enhance
the
energy
of
germination
and
germination
percentage
[95].
Dzung
and
Thang
[96]
suggested
that
chitosan
could
enhance
growth
and
yield
in
soybean.
Seed
soaked
with
chitosan
increased
germination
rate,
length
and
weight
of
hypocotyls
and
radicle
in
rapeseed
[148].
Chandrkrachang
[94]
also
found
that
the
application
of
chitosan
could
increase
the
germination
rate
of
cucumber,
chilli,
pumpkin
and
cabbage.
Manjunatha
et
al.
[107]
reported
that
seed
priming
with
chitosan
enhances
seed
germination
and
seedling
vigor
in
pearl
millet.
Further,
it
is
also
noticed
that
seed
priming
with
acidic
chitosan
solutions
improved
the
maize
vigor
[101].
Similarly,
rice
seedlings
treated
with
chitosan
induced
defense
responses
against
the
rice
blast
pathogen,
Magnaporthe
grisea
by
inducing
the
production
of
the
phytoalexins
(sakuranetin
and
monilactone
A)
in
leaves
[104].
Moreover,
chitosan
also
stimulated
the
growth
and
yield
of
rice
along
with
reinforcing
the
defense
response
[149].
In
addition,
other
studies
also
supported
a
role
of
chitosan
in
modulating
the
plant
response
to
several
abiotic
stresses
including
salt
and
water
stress
[121,138,150].
For
instance,
Boonlertnirun
et
al.
[151]
found
that
chitosan
treatments
had
a
significant
effect
on
the
growth
or
yield
of
drought-stressed
rice
plants
compared
to

P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
41
Table
4
Pros
and
cons
of
various
strategies
used
for
the
synthesis
of
chitosan
encapsulated
active
compounds.
Strategies
Pros
Cons
Reference(s)
Ionotropic
gelation
Simple
and
mild
procedure;
no
chemical
cross-linking;
reduce
the
possible
toxic
side
effects
of
chemicals
or
reagents
used
in
the
procedure;
and
better
control
of
degradation
kinetics
Release
of
active
ingredient
depends
on
molecular
weight,
degree
of
deacetylation,
and
concentration
of
chitosan
[66,158–162]
Emulsion
cross-linking
High
drug
loading
efficiency;
controlled
release
with
improved
bioavailability;
and
easy
to
control
particle
size
Tedious
process,
uses
harsh
crosslinking
agents,
problem
of
reactivity
of
active
agent
with
cross-linking
agent,
and
challenge
of
complete
removal
of
unreacted
cross-linking
agent
[40,66,159,161,163]
Emulsion-droplet
coalescence
High
loading
efficiency
and
smaller
particle
size
Particle
size
depends
on
the
degree
of
deacetylation
of
chitosan.
The
decreased
degree
of
deacetylation
increases
particle
size
which
in
turn
decreases
drug
content
[66,164]
Precipitation
Efficient
control
of
particle
size
and
drug
release;
and
avoids
the
use
of
toxic
organic
solvents
Partial
protection
of
the
loaded
active
agent
from
nuclease
degradation
[40,159]
Reverse
micellar
method Thermodynamically
stable
particle
size
with
suitable
polydispersity
index;
and
narrow
size
distribution
with
smaller
particle
size
Tedious
and
laborious
process [40,66]
Sieving
method
Simple
procedure
and
can
be
easily
scaled
up
Irregular
particle
shape
[165]
Spray
drying
method
High
drug
stability,
good
entrapment
efficiency,
prolonged
drug
release
attributes
and
useful
method
to
prepare
powder
formulation
Particle
size
depends
on
size
of
nozzle,
spray
flow
rate,
pressure
inlet
air
temperature;
and
encapsulation
efficiency
depends
on
the
molecular
weight
of
chitosan
[40,159]
control
plants.
It
is
interesting
to
note
that
the
effect
was
greatest
when
chitosan
was
applied
before
the
onset
of
stressful
conditions.
Bittelli
et
al.
[91]
also
noticed
that
the
water
use
of
pepper
plants
treated
with
chitosan
reduced
by
26–43%,
with
no
significant
change
in
biomass
production
or
yield.
These
findings
indicate
that
chitosan
has
potential
to
be
developed
as
an
antitranspirant
in
agricultural
situations
where
excessive
water
loss
is
undesirable.
Recently,
chitosan
coatings
have
emerged
as
an
ideal
alterna-
tive
to
chemically
synthesized
pesticides.
It
has
been
reported
to
reduce
the
growth
of
decay
and
induced
resistance
in
the
host
tissue
[152].
Chitosan
can
also
help
to
protect
the
safety
of
edi-
ble
products.
The
protection
of
fresh
cut
broccoli
with
chitosan
against
E.
coli
and
Listeria
monocytogenes
was
assisted
with
bioac-
tive
components
such
as
bee
pollen
and
extracts
from
propolis
and
pomegranate
[153].
Chitosan
protection
by
exclusion
occurs
with
soybean
seed
treatments.
In
this
case
the
major
advantage
was
pro-
tection
from
insects
such
as
agarotis,
ypsilon,
soybean
pod
borer,
and
soybean
aphids.
Additionally,
the
treatment
was
also
accom-
panied
by
increases
in
seed
germination,
plant
growth
and
soybean
yield.
From
the
above
points,
it
is
clear
that
the
chitosan
products
are
more
effective
and
can
be
used
in
a
numbers
of
ways
to
reduce
disease
levels
and
enhance
crop
productivity
in
a
eco-friendly
and
sustainable
manner.
1.2.
Chitosan
as
a
promising
delivery
system
Chitosan
is
one
of
the
most
widely
used
polymers
in
the
field
of
drug
delivery.
Its
attractiveness
relies
on
its
useful
structural
and
biological
properties
[154,155],
which
include
a
cationic
char-
acter,
solubility
in
aqueous
acidic
media,
and
biodegradability.
Chitosan
has
a
low
solubility
at
physiological
pH
of
7.4
as
it
is
a
weak
base
(pKa6.2–7).
Chitosan
is
synthesized
by
removing
the
acetate
moiety
from
chitin
through
amide
hydrolysis
under
alkaline
conditions
(concentrated
NaOH)
or
through
enzymatic
hydrolysis
in
the
presence
of
chitin
deacetylase
[156].
Chitosan’s
amine
groups
readily
complex
with
a
variety
of
oppositely
charged
polymers
such
as
poly(acrylic
acid),
sodium
salt
of
poly(acrylic
acid),
carboxymethyl
cellulose,
xanthan,
carrageenan,
alginate
and
pectin,
etc.
[157].
Chitosan
also
provides
considerable
flexibility
for
development
of
formulation,
as
it
is
available
in
wide
range
of
molecular
weights
(500–1400
kDa)
and
degrees
of
acetylation.
Chitosan’s
amine
group
also
readily
lends
itself
to
other
chem-
ical
modifications.
Chitosan
easily
absorbs
to
plant
surfaces
(e.g.
leaf
and
stems),
which
helps
to
prolong
the
contact
time
between
agrochemicals
and
the
target
absorptive
surface.
Chitosan
nanopar-
ticles
are
known
to
facilitate
active
molecule
or
compound
uptake
through
the
cell
membrane.
The
absorption
enhancing
effect
of
chi-
tosan
nanoparticles
improves
the
molecular
bioavailability
of
the
active
ingredients
contained
within
the
nanoparticles
[158].
Taken
together,
these
advantages
indicate
that
chitosan
has
a
bright
future
as
a
drug
delivery
system
in
the
field
of
sustainable
agriculture.
1.3.
Strategies
for
production
of
chitosan
nanoparticles
Chitosan
nanoparicles
can
be
synthesized
by
various
techniques
viz.,
emulsion
cross-linking,
emulsion-droplet
coalescence,
precip-
itation,
ionotropic
gelation,
reverse
micelles
and
sieving
through
nano-scaled
controlled
release
devices.
A
comparison
of
these
tech-
niques,
their
merits
and
demerits
are
summarized
in
Table
4.
The
selection
of
methods
for
chitosan
nanoparticles
synthesis
depends
on
requirements
such
as
the
particle
size
and
shape,
thermal
sta-
bility,
release
time
of
the
active
ingredients,
and
residual
toxicity
of
the
final
product.
1.4.
Emulsion
cross-linking
Emulsions
are
a
standard
process
leading
to
nanoparticulate
phases,
while
cross-linking
is
a
common
way
to
stabilize
a
par-
ticle
structure
and
to
manipulate
the
controlled-release
properties
of
that
particle.
Altering
the
cross-linking
degree
of
a
particle
modifies
an
agrochemical’s
permeability
through
it.
Cross-linking
enhances
the
mechanical
strength
of
the
final
particle
by
introduc-
ing
a
three-dimensional
network
structure
into
the
nano-emulsion.
The
process
begins
when
a
chitosan
solution
is
emulsified
in
an
oil
phase
(water-in-oil
emulsion).
The
chitosan
phase
is
first
stabilized
by
a
suitable
surfactant,
and
is
then
reacted
with
an
appropriate
cross
linking
agent
(e.g.
formaldehyde,
glutaraldehyde,
genipin,
glyoxal,
etc.).
This
is
followed
by
washing
and
drying
of
the
resulting
nanoparticles
[159].
This
method
is
schematically
represented
in
Fig.
2(A)
.
The
particle
size
is
mainly
determined

42
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Kashyap
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/
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of
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77
(2015)
36–51
Fig.
2.
Schematic
representation
of
various
methods
for
the
synthesis
of
chitosan
nanoparticles.
(A)
Emulsion
cross-linking;
(B)
emulsion-droplet
coalescence;
(C)
ionotropic
gelation;
(D)
precipitation;
(E)
reverse
micelles;
(F)
sieving;
and
(G)
spray
drying.
The
term
‘drug’
is
used
to
represent
an
agrochemical
compound,
micronutrient
and
genetic
material,
etc.

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77
(2015)
36–51
43
Fig.
2.
(Continued
).
by
the
size
of
the
emulsion
droplet,
which
in
turn
is
dependent
on
the
type
of
surfactant,
degree
of
crosslinking
and
the
stirring
speed
[166].
The
molecular
weight
and
concentration
of
chitosan
also
affect
the
preparation
and
performance
of
the
nanoparti-
cles
[40,167].
The
major
drawback
of
this
method
is
that
it
is
somewhat
tedious
and
the
use
of
harsh,
and
often
expensive,
cross-
linking
agents
can
induce
undesirable
chemical
reactions
with
the
active
agent.
Recently,
Fan
et
al.
[47]
studied
the
synthesis
and
controlled
release
characteristics
of
auxin-loaded
chitosan
micro-
spheres
using
a
cross-linker.
They
found
that
the
cumulative
release

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of
the
auxins
from
the
particles
reached
a
maximum
(60%)
after
about
120
h.
They
also
observed
that
maximum
encapsulation
effi-
ciency
was
significantly
influenced
by
the
type
of
cross-linker,
cross-linking
time
and
the
oil/water
phase
ratio.
Based
on
these
results
this
procedure
is
suitable
to
prepare
chitosan
nanoparticles
for
prolonged
controlled
release
of
compounds,
possibly
spanning
weeks
or
months,
and
do
so
with
greater
safety
to
non-target
orga-
nisms.
1.5.
Emulsion-droplet
coalescence
This
method
follows
the
principles
of
emulsion
by
cross-linking
but
uses
precipitation
techniques
[168,169].
An
emulsion
is
first
prepared
by
dispersing
chitosan
solution
and
liquid
paraffin
oil.
The
active
ingredient
and
a
sodium
hydroxide
solution
are
combined
and
added
to
the
first
emulsion
to
produce
additional
droplets.
High-speed
mixing
is
then
used
to
generate
collisions
between
the
different
droplets,
randomly
combining
them
and
precipitating
particles
of
small
size
[169].
The
particle
size
depends
primarily
on
the
degree
of
deacetylation
of
chitosan.
Generally,
at
lower
degree
of
deacetylation,
large
size
particles
with
less
ability
to
retain
the
active
ingredients
are
obtained
[170].
The
pictorial
representation
of
the
method
is
shown
in
Fig.
2B.
Using
this
procedure,
Toku-
mistu
et
al.
[164]
synthesized
gadopentetic
acid
loaded
chitosan
nanoparticles
(452
nm)
with
45%
drug
loading
efficiency.
A
similar
methodology
has
been
adopted
by
Anto
et
al.
[168]
to
encapsulate
5-fluorouracil.
Interestingly,
when
two
emulsions
with
equal
outer
phase
are
mixed
together,
droplets
of
each
collide
randomly
and
coalesce,
resulting
in
final
droplets
with
uniform
content.
1.6.
Ionotropic
gelation
The
chitosan
nanoparticles
produced
through
this
method
are
stable,
non-toxic
and
organic
solvent
free
[41,48,169–172].
It
is
very
simple,
and
employs
the
use
of
oppositely
charged
complexes
(polyanions)
to
bond
to
the
oppositely
charged
amino
groups
of
chi-
tosan
(NH3+).
Tripolyphosphate
(TPP)
is
the
most
commonly
used
ionic
cross-linker,
and
relies
on
electrostatic
interaction
instead
of
chemical
cross-linking,
avoiding
the
possible
toxicity
of
reagents
and
other
adverse
reactions.
However,
the
cross-linking
is
pH-
dependent.
In
this
procedure,
chitosan
is
dissolved
in
a
weak
acidic
medium
and
added
drop
wise
under
constant
stirring
to
an
aqueous
solution
containing
the
other
reagents
(Fig.
2C).
Due
to
the
com-
plexation
between
oppositely
charged
species,
chitosan
undergoes
ionic
gelation
and
the
spherical
nanoparticles
precipitate
[173].
The
chitosan/TPP
molar
ratio
largely
controls
the
mean
diameter
of
the
nanoparticles,
which
can
also
affect
the
drug
release
characteristics.
Interestingly,
the
mechanism
of
nanoparticle
formation
through
ionic
gelation
is
well
described
by
several
workers
[174,175].
It
has
been
suggested
that
all
ionic
groups
of
TPP
participated
in
interac-
tions
with
chitosan
amine
groups.
The
ion
pairs,
formed
through
the
negatively
charged
TPP
with
the
protonated
amine
function-
ality
of
chitosan
in
ionotropic
gelation
provided
chitosan
with
an
amphoteric
character,
which
enhanced
the
protein
adhesion
and
subsequently
accelerated
the
attachment
of
anchorage
dependant
cells.
Recently,
Koukaras
et
al.
[174]
provided
insights
into
the
intermolecular
interactions
responsible
for
the
ionic
cross-linking
during
ionotropic
gelation
by
means
of
all
electron
density
func-
tional
theory.
They
reported
that
the
maximum-interaction
relative
configurations
of
TPP
and
chitosan
oligomers
depended
on
the
pri-
mary
ionic
cross-linking
types
(H-,
M-
and
T-links).
In
all
three
of
the
linking
types,
there
is
a
high
degree
of
correspondence
between
chi-
tosan
monomers
and
TPP
polyanions,
and
thus,
these
correspond
to
low
#
(and
!)
ratios.
As
a
result,
at
low
#
ratios,
the
high
con-
centration
of
TPP
permits
the
formation
of
dense
H-links.
At
high
#
(and
!)
ratios,
the
dihedral
bias
deters
the
formation
of
parallel
CS
chains
and
impels
the
formation
of
irregular
and
smaller
size
nanoparticle
cores.
At
even
higher
#
ratios,
the
very
low
concen-
tration
of
TPP
results
in
low
nanoparticle
core
densities
because
of
the
increased
distance
between
successive
H-links,
ultimately
lead-
ing
to
an
increased
nanoparticle
size.
Besides
this,
a
recent
work
on
chitosan/TPP
nanoparticles
has
also
established
that
the
concentra-
tion
of
acetic
acid
used
to
dissolve
chitosan
and
the
temperature
at
which
the
cross-linking
process
occurs,
strongly
affect
the
size
dis-
tribution
of
the
obtained
nanoparticles
[176].
Fàbregasa
et
al.
[177]
found
that
the
stirring
speed
during
ionic
gelation
significantly
affect
reaction
yield.
Therefore,
manipulation
of
this
parameter
can
be
used
to
give
some
control
over
size
range
that
is
obtained
to
favor
the
maximum
yield
of
nanoparticles
of
desired
size.
1.7.
Precipitation
This
method
is
quite
simple.
Chitosan
nanoparticles
are
pro-
duced
by
blowing
a
chitosan
solution
into
an
alkaline
solution
[e.g.
NaOH(aq)]
or
methanol.
The
blowing
is
accomplished
with
a
com-
pressed
air
nozzle,
thereby
forming
the
coacervate
particles.
These
are
separated
and
purified
by
filtration
and
followed
by
washing
with
hot
and
cold
water
[178].
The
method
is
schematically
repre-
sented
in
Fig.
2D.
Generally,
various
parameters
viz.,
compressed
air
pressure,
spray
nozzle
diameter
and
chitosan
concentration
affects
the
particle
shape
and
size.
Although
this
method
is
simple,
cross-
linking
is
required
to
enhance
the
particle
stability,
and
even
then
particles
have
weak
mechanical
strength
and
irregular
morphol-
ogy.
1.8.
Reverse
micelles
This
method
uses
a
thermodynamically
stable
mixture
of
water,
oil
and
lipophilic
surfactant.
Using
this
method,
it
is
possible
to
obtain
very
small
polymeric
nanoparticles
(≤10
nm)
with
a
uniform
distribution
compared
with
other
methods.
The
size,
polydisper-
sity
and
thermodynamic
stability
of
the
particles
are
maintained
in
a
dynamic
equilibrium
system.
Briefly,
the
method
consists
of
preparing
a
surfactant
solution
(e.g.
sodium
bis(ethyl
hexyl)
sul-
fosuccinate
or
cetyl
trimethylammonium
bromide)
in
an
organic
solvent
(e.g.
n-hexane),
to
which
a
chitosan
solution
and
the
active
ingredient
are
added
under
constant
stirring,
forming
a
transpar-
ent
mini-
or
micro-emulsion.
Subsequently,
a
cross-linking
agent
(e.g.
glutaraldehyde)
is
added
and
the
system
is
maintained
under
constant
agitation.
The
organic
solvent
is
then
evaporated,
pro-
ducing
a
dry
and
transparent
mass
that
is
dispersed
in
water.
A
salt
is
then
added
to
this
system,
which
precipitates
the
surfac-
tant.
The
resulting
mixture
is
centrifuged
and
the
supernatant,
containing
nanoparticles
loaded
with
the
active
substance,
is
col-
lected.
The
nanoparticles
are
separated
by
dialysis
and
lyophilized
to
obtain
a
dry
powder
[165].
The
method
is
schematically
repre-
sented
in
Fig.
2E.
Brunel
et
al.
[179]
used
a
reverse
micellar
method
to
prepare
chitosan
nanoparticles.
They
emphasized
that
chitosan
of
low
molecular
weight
is
preferable
to
achieve
better
control
over
particle
size
and
distribution.
This
may
be
due
to
a
reduction
in
the
viscosity
of
the
internal
aqueous
phase
or
entanglement
of
the
polymer
chains
during
the
process.
In
recent
times,
this
method
has
been
use
for
enzyme
immobilization
[180]
and
to
encapsulate
oligonucleotides
[181].
To
date,
despite
some
of
the
advantages,
the
use
of
this
method
to
produce
chitosan
nanoparticles
is
limited,
due
to
the
difficulty
of
isolating
the
nanoparticles
and
need
to
use
a
large
quantity
of
organic
solvent.
1.9.
Seiving
method
This
method
involves
the
cross-linking
of
an
aqueous
acidic
solution
of
chitosan
using
glutaraldehyde.
The
cross-linked

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45
chitosan
is
then
passed
through
a
sieve
with
suitable
mesh
size
to
obtain
microparticles.
The
microparticles
are
then
washed
with
sodium
hydroxide
(0.1
N)
solution
to
remove
the
unreacted
glutataraldehyde
and
dried
at
40 ◦C
[159].
This
method
does
not
seem
to
be
being
extensively
researched
for
agricultural
use.
The
method
is
schematically
shown
in
Fig.
2F.
1.10.
Spray
drying
This
method
is
extensively
used
for
the
production
of
matri-
ces
to
produce
dry
powders,
granules
and
pellets
from
chitosan
solutions
and
suspensions
[160].
The
technique
is
quite
versatile
and
can
be
used
for
drugs
with
high
or
low
heat-sensitivity
and
with
high
or
low
water
solubility,
and
hydrophilic
or
hydropho-
bic
polymers
[182].
This
procedure
is
inexpensive
and
employs
a
single
step
to
produce
small-sized
particles
that
are
typically
micro-sized,
and
then
these
particles
are
often
reformulate
into
suspensions,
capsules
or
tablets
[183].
This
technique
uses
a
chi-
tosan
solution
in
acetic
acid,
to
which
the
active
ingredient
and
the
cross-linking
agent
(glutaraldehyde
or
sodium
tripolyphosphate)
are
consecutively
added
(Fig.
2G).
The
resulting
solution
is
atom-
ized
through
a
hot
air
stream,
causing
flash
evaporation
of
the
solvent
to
form
the
desired
particles
[184].
The
important
parame-
ters
to
modulate
particle
size
in
this
process
are
the
type
of
needle,
flow
speed
of
the
compressed
air,
air
temperature
and
degree
of
cross-linking
[185].
This
method
can
be
used
to
synthesize
particles
with
or
without
cross-linking,
and
has
been
used
to
prepare
chi-
tosan
micro-particles
for
the
delivery
of
cimetidine,
famotidine
and
nizatidine
[186].
Recently,
Tokárová
et
al.
[187]
used
spray-dried
chitosan
microcarriers
for
the
delivery
of
silver
nanoparticles.
1.11.
Strategies
for
loading
active
ingredient
into
chitosan
nanoparticles
Loading
active
ingredient
into
nanoparticulate
systems
can
be
done
at
the
time
of
preparation
of
particles
(incorporation)
or
after
the
formation
of
particles
(incubation).
In
these
systems,
the
active
ingredient
is
physically
embedded
within
the
matrix
or
adsorbed
on
the
surface.
Various
techniques
have
been
developed
to
improve
the
efficiency
of
loading
the
active
ingredient,
but
the
efficiency
largely
depends
on
the
method
of
preparation
and
the
physico-
chemical
properties
of
the
substance.
Loading
efficiency
is
generally
maximized
when
the
substance
is
incorporated
during
the
forma-
tion
of
particles,
while
incubations
typically
give
a
much
lower
degree
of
incorporation.
However,
the
degree
of
incorporation
is
also
influenced
by
the
specific
process
parameters
such
as
exact
method
of
preparation,
presence
of
additives
(e.g.
cross
linking
agent,
surfactant
stabilizers,
etc.),
and
agitation
intensity
[159].
Both
hydrophillic
and
hydrophobic
compounds
can
be
loaded
into
chitosan-based
particulate
systems.
Water-soluble
compounds
are
mixed
with
chitosan
solution
to
form
a
homogeneous
mixture,
and
then,
particles
can
be
produced
by
any
of
the
methods
described
earlier
in
the
section.
Water-insoluble
compounds
that
precipitate
in
the
acidic
chitosan
solutions
can
be
incorporated
after
particle
preparation
by
soaking
the
preformed
particles
with
a
saturated
solution
of
the
active
ingredient.
Water-insoluble
drugs
can
also
be
loaded
using
a
multiple
emulsion
technique.
In
this
method,
compound
is
dissolved
into
a
suitable
solvent
and
then
emulsi-
fied
in
the
chitosan
solution
to
form
an
oil-in-water
type
emulsion.
Sometimes,
compounds
can
be
dispersed
within
a
chitosan
solution
by
using
a
surfactant
to
form
a
suspension.
The
oil
in
water
(o/w)
emulsions
or
suspensions
prepared
in
this
manner
can
be
further
emulsified
into
liquid
paraffin
to
get
oil-water-oil
multiple
emul-
sions.
The
resulting
droplets
can
be
hardened
by
using
a
suitable
cross-linking
agent.
1.12.
Release
kinetics
of
active
ingredients
from
chitosan
nanoparticles
The
release
of
an
active
ingredient
from
chitosan-based
parti-
cles
depends
upon
the
morphology,
size,
density,
and
extent
and
rate
of
cross-linking
of
the
particles,
as
well
as
the
physicochemical
properties
of
the
drug.
If
any
adjuvant
is
used
this
can
also
affect
the
release
rate.
Studies
showed
that
under
in
vitro
conditions,
the
release
of
an
active
ingredient
is
affected
by
pH,
solvent
polarity,
and
the
presence
of
enzymes
in
the
dissolution
media
[188,189].
Generally,
the
release
of
drug
from
chitosan
particles
occurs
by
one,
or
a
combination
of
three
different
mechanisms:
(i)
an
osmot-
ically
driven
burst
mechanism,
(ii)
a
diffusion
mechanism,
and
(iii)
erosion
or
degradation
of
the
polymer.
In
agricultural
systems
the
release
mechanisms
are
by
diffusion
release
and/or
degradation
release.
The
diffusion
release
mechanism
includes
several
steps
viz.,
(i)
penetration
of
water
into
particulate
system,
which
causes
swelling
of
the
matrix;
(ii)
conversion
of
a
glassy
polymer
into
a
plasticized
or
rubbery
swollen
matrix,
and
(iii)
diffusion
of
com-
pound
from
the
swollen
matrix.
The
original
active
ingredient
content
contained
in
chitosan
par-
ticles
is
determined
in
different
ways,
but
the
release
from
the
chitosan
particles,
is
typically
measured
from
particles
placed
in
phosphate
buffer
saline
(PSB;
pH
7.4)
and
kept
in
a
thermostatic
incubator
at
37 ◦C.
Specified
volumes
of
the
buffered
medium
are
removed
at
regular
intervals
from
the
sample
being
analyzed,
and
that
same
amount
of
fresh
buffer
is
added
back
into
the
flask
to
keep
the
total
solution
volume
constant
throughout
the
duration
of
the
study.
The
aliquot
of
removed
sample
is
then
filtered
and
the
transparent
filtrate
is
analyzed.
The
quantity
of
active
ingre-
dient
in
the
aliquot
is
typically
determined
by
spectroscopic
or
chromatographic
methods.
Diffusion
release
of
active
ingredient
is
typical
for
hydrophilic
polymers
that
form
hydrogels
(e.g.
polyvinyl
alcohol),
while
dif-
fusion
and
degradation
release
occurs
with
chitosan.
It
is
not
uncommon
to
observe
an
initial
“burst”
release
of
active
ingre-
dient
from
particles
that
predominantly
release
active
ingredient
by
diffusion
or
degradation.
This
happens
due
to
the
adsorption
of
active
ingredients
onto
the
surface
of
the
particles.
Once
this
burst
is
exhausted,
a
slow
and
steady
release
is
observed
that
accel-
erates
if
and
when
the
particle
matrix
begins
to
degrade.
Kweon
and
Kang
[190]
synthesized
chitosan–polyvinylalcohol
(PVA)
par-
ticles
to
study
the
compound
release
mechanism
of
the
active
ingredient
under
various
conditions.
They
calculated
the
diffusion
controlled
release
by
analysis
of
the
linear
relationship
between
the
amount
of
active
ingredient
released
and
the
square
root
of
the
time.
Jamnongkan
and
Kaewpirom
[51]
demonstrated
potas-
sium
release
kinetics
and
water
retention
of
controlled-release
fertilizers
based
on
chitosan
hydrogels
is
through
a
quasi-Fickian
diffusion
mechanism.
Similarly,
Jameela
et
al.
[191]
obtained
a
good
correlation
fit
for
the
cumulative
drug
released
vs.
square
root
of
time,
demonstrating
that
the
drug
release
from
the
microsphere
matrix
is
diffusion-controlled
and
obeys
the
Higuchi
equation
[190].
It
was
demonstrated
that
the
rate
of
release
depends
upon
the
size
of
microspheres.
Orienti
et
al.
[192]
studied
the
correlation
between
matrix
erosion
and
release
kinetics
of
indomethacin-
loaded
chitosan
microspheres.
Release
kinetics
was
correlated
with
the
concentration
of
chitosan
in
the
microsphere
and
pH
of
the
release
medium.
Nam
and
Park
[188]
have
demonstrated
the
in
vitro
release
test
of
drug
loaded
chitosan
microspheres.
Agni-
hotri
and
Aminabhavi
[165]
also
analyzed
the
dynamic
swelling
data
of
chitosan
microparticles
and
concluded
that
with
increase
in
cross-linking,
swelling
of
chitosan
microparticles
decreases.
Recently,
Khan
and
Ranjha
[193]
studied
the
swelling
behavior
of
chitosan/poly(vinyl
alcohol)
hydrogels
as
a
function
of
pH,
poly-
meric
compositions
and
degree
of
cross-linking.
They
noticed
that

46
P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
swelling
increased
by
increasing
poly(vinyl
alcohol)
contents
in
the
structure
of
hydrogels
at
higher
pH.
They
also
observed
that
the
cross-linking
ratio
was
inversely
related
with
the
swelling
of
hydrogels.
Similar
results
were
also
described
by
Martínez-
Ruvalcaba
et
al.
[194],
where
drug
release
increased
with
increasing
drug
contents
in
the
hydrogels,
while
release
of
drug
decreased
as
the
ratio
of
crosslinking
agent
increased
in
the
hydrogel
struc-
ture
owing
to
strong
physical
entanglements
between
polymers.
It
is
also
important
to
note
that
the
release
rate
of
drugs
from
hydrophilic
matrices
based
on
chitosan
is
greatly
affected
by
changes
in
pH.
The
increase
in
release
rates
could
be
due
to
an
associated
increase
in
the
fluid-filled
cavities
created
by
dissolu-
tion
and
diffusion
of
the
drug
particles
near
the
surface,
which
in
turn
results
in
an
increase
in
the
permeability
of
the
drug
[195].
2.
Applications
of
chitosan
nanoparticles
as
a
delivery
system
2.1.
Pesticide
delivery
for
crop
protection
The
difficulties
in
controlling
pests
along
with
concern
about
the
indiscriminate
use
of
pesticides
in
agriculture
have
been
the
subject
of
intense
debate
and
discussion.
The
pressure
to
devise
alternative
methods
of
pest
control,
to
reduce
the
dependency
on
synthetic
pesticides
and
reduce
residue
problem,
is
rising
steadily.
There
are
several
examples
of
slow
release
of
encapsulated
agrochemi-
cals
by
polymeric
nanoparticles.
For
example,
Liu
et
al.
[196]
used
polyvinylpyridine
and
polyvinylpyridine-co-styrene
nanoparticles
to
control
release
of
tebuconazole
and
chlorothalonil
fungicides
for
solid
wood
preservation.
That
method
has
given
near
quan-
titative
incorporation
of
the
active
ingredient.
A
few
years
later
polymeric
nanocapsules
were
described
as
vehicles
for
the
pesti-
cides
ivermectin
and
acetamiprid
[197],
while
Wang
et
al.
[198]
used
nanosized
inorganic
particles
such
as
TiO2,
SiO2,
Fe2O3,
or
Al2O3as
pesticide
carriers
for
increased
bioactivity
and
reduc-
tion
in
residues.
Boehm
et
al.
[199]
obtained
stable
polymeric
nanospheres
(135
nm)
with
3.5%
encapsulation
rate
and
despite
the
low
active
ingredient
content,
this
formulation
yielded
signif-
icant
improvements
in
the
bioavailability
of
the
insecticide
(RPA
107382)
to
plants.
These
researchers
also
performed
biological
studies
on
cotton
plants
infested
with
aphids
to
estimate
the
direct
contact
efficacy
of
nanosphere
formulations
on
insects.
The
nanosphere
formulations
performed
better
than
the
classical
sus-
pension
to
manage
the
infestation.
It
is
important
to
note
that
the
developed
nanosphere
formulations
are
not
better
than
the
clas-
sical
suspension
in
terms
of
speed
of
action
and
sustained
release.
Nevertheless,
nanosphere
formulation
performed
better
than
the
classical
suspension
to
enhance
the
systemicity
of
the
active
ingre-
dient
and
improve
its
penetration
through
the
plant.
It
has
been
reported
that
nanoparticles
loaded
with
essential
garlic
oil
are
effective
against
Tribolium
castaneum
[20].
It
has
also
been
reported
that
aluminosilicate-filled
nanotubes
stick
to
plant
surfaces
while
the
nanoscale
aluminosilicate
particles
leach
from
the
nanotubes
and
subsequently
stick
to
the
surface
hair
of
insect
pests.
These
particles
ultimately
enter
the
body
and
influence
certain
physio-
logical
functions
[200,201].
Recently,
a
pesticide
company
released
an
aqueous
dispersion
formulated
with
nano-sized
biocide
(Ban-
ner
MAXX®from
Syngenta)
having
a
broad
spectrum
systemic
fungicidal
action.
The
active
ingredient
controls
leaf
spots,
blights,
rusts
and
powdery
mildew
diseases
on
various
horticultural
and
ornamental
crops
[17,202].
At
present,
there
are
several
reports
available
regarding
the
production
and
use
of
chitosan
nanoparti-
cles
as
a
delivery
matrix
for
the
release
of
pesticides
in
agriculture.
As
an
example,
Paula
et
al.
[203]
prepared
and
characterized
micro-
spheres
composed
of
chitosan
and
cashew
tree
gum,
which
were
used
as
carriers
of
the
essential
oil
of
Lippia
sidoides,
which
pos-
sesses
insecticidal
properties.
The
findings
indicated
the
suitability
of
chitosan
for
use
as
matrices
to
carry
bioinsecticides
designed
to
control
the
proliferation
of
insect
larvae.
Similarly,
microcapsules
of
alginate
and
chitosan
were
prepared,
characterized,
and
evalu-
ated
as
a
carrier
system
for
imidacloprid
[55].
The
particles
obtained
were
stable
and
imidacloprid
was
encapsulated
with
an
efficiency
of
around
82%.
In
release
assays,
it
was
shown
that
the
release
time
of
the
encapsulated
insecticide
was
up
to
eight
times
longer,
compared
to
the
free
insecticide,
and
that
alterations
in
the
con-
centrations
of
alginate
and
chitosan
affected
the
release
profile.
In
another
independent
study,
Qui˜
nones
et
al.
[57]
described
the
use
of
chitosan
microspheres
to
carry
synthetic
analogs
of
brassinos-
teroids
and
diosgenin
derivatives.
The
release
kinetics
assay
using
water
revealed
that
the
least
efficiently
encapsulated
steroids
were
released
fastest
from
the
particles.
These
results
demonstrate
that
molecular
modifications
can
be
used
to
design
effective
systems
for
the
delivery
and
release
of
agrochemicals.
Besides
this,
amphiphilic
derivative
of
chitosan,
N-(octadecanol-1-glycidyl
ether)-O-sulfate
chitosan
has
been
evaluated
as
a
carrier
for
the
insecticide
rotenone
[60].
The
polymeric
micelles
formed
were
spherical,
with
a
size
range
of
between
167
and
204
nm,
and
the
nanoparticles
were
formed
by
self-assembly
in
aqueous
solution.
The
encapsulation
of
rotenone
increased
its
solubility
in
water
1300-fold,
while
in
vitro
release
assays
demonstrated
that
the
nanoparticles
provided
sus-
tained
release
of
the
insecticide.
The
properties
of
nanomicelles
based
on
NOSCS
enable
them
to
be
used
as
carriers
to
encapsulate
and
subsequently
release
insoluble
pesticides
employed
in
agri-
culture.
Feng
and
Peng
[204]
synthesized
a
new
compound
based
on
chitosan,
using
carboxymethyl
chitosan
(CM-C)
with
ricinoleic
acid
(RA)
for
use
as
a
carrier
of
the
biopesticide
azadirachtin
(AZA).
The
particles
presented
good
polydispersion,
with
a
size
range
of
200–500
nm,
as
well
as
smooth
spherical
morphology
and
high
zeta
potential.
The
AZA
encapsulation
efficiency
was
56%,
and
the
par-
ticles
were
able
to
release
the
pesticide
over
a
period
of
11
days.
The
use
of
the
carrier
assisted
the
solubilization
in
water
of
this
lipid-soluble
pesticide,
and
could
therefore
offer
advantages
in
agri-
cultural
applications.
2.2.
Fertilizer
delivery
for
balanced
and
sustained
nutrition
The
extent
and
quality
of
plant
growth
is
largely
dependent
on
the
quantity
of
fertilizer
and
water.
So,
improvement
in
crop
outcomes
requires
improved
utilization
of
water
resources
and
fertilizer
nutrients.
It
is
estimated
that
about
40–70%
of
nitrogen,
80–90%
of
phosphorus,
and
50–70%
of
potassium
of
the
applied
fertilizers
is
lost
to
the
environment
and
cannot
be
absorbed
by
the
intended
plants.
This
is
not
only
a
substantial
monetary
and
resource
loss
but
also
results
in
serious
environmental
pollution
[50,205].
Several
recent
research
studies
have
been
published
that
describe
the
use
of
superabsorbent
polymers
to
enhance
germination
and
crop
growth
under
arid
and
desert
environments.
The
results
are
encouraging,
and
show
that
use
of
such
materials
can
reduce
water
consumption
in
irrigation,
and
reduce
the
plant
death
rate
[206,207].
An
optimized
combination
of
slow
release
fertilizers
and
superabsorbent
polymers
may
not
only
significantly
improve
plant
nutrition
and
yields,
but
might
be
a
method
to
mitigate
the
stressed
environmental
impact,
reduce
water
losses
to
evaporation,
and
reduce
irrigation
frequency
[208].
Indeed,
the
development
of
slow
release
fertilizers
from
chitosan
nano-
or
microparticles
is
a
relatively
new
concept
to
reduce
fertilizer
con-
sumption
and
to
minimize
environmental
pollution.
With
these
principles
in
mind,
Wu
et
al.
[209]
developed
a
chitosan-coated
NPK
compound
fertilizer
with
both
controlled-release
and
water-
retention
capabilities,
by
using
an
inner
coating
of
chitosan,
and
an
outer
coating
was
poly
(acrylic
acid-co
acrylamide)
[P(AA-co-AM)],

P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
47
which
is
a
superabsorbent
polymer.
It
was
observed
that
the
prod-
uct
showed
a
slow
controlled
release
of
the
nutrients.
The
nutrients
released
did
not
exceed
75%
on
the
30th
day.
Furthermore,
chitosan
is
a
readily
biodegradable
material,
while
the
P(AA-co-AM)
can
also
be
degraded
in
soil,
so
neither
the
matrix
polymers
nor
their
degraded
products
were
harmful
to
the
soil.
We
believe
that
such
products
have
a
great
potential
as
eco-friendly
nano-fertilizers,
especially
in
drought-prone
regions
with
limited
water
availability.
In
similar
efforts,
Corradini
et
al.
[50]
explored
the
possibility
of
utilizing
chitosan
nanoparticles
for
slow
release
of
NPK
fertilizer,
while
Hussain
et
al.
[43]
reported
controlled
release
of
urea
from
chitosan
microspheres.
Although
preparation
of
nanoparticles
as
controlled
release
devices
may
be
more
costly
than
simple
broad
application
of
fertilizer,
it
is
clear
that
these
materials
can
not
only
synchronize
the
release
of
nitrogen,
phosphorous
and
potassium
fertilizer
for
their
optimum
uptake
by
crops,
but
they
can
also
prevent
undesirable
nutrient
losses
to
soil,
water,
and
air.
This
has
the
compensatory
benefits
of
requiring
less
use
of
fertilizers,
as
well
as
undesirable
environmental
impact.
Nevertheless,
because
of
the
“upfront”
higher
costs,
it
is
clear
that
if
the
materials
in
development
are
to
become
commercial
successes,
they
will
need
to
offer
better
value
to
growers
by
reducing
the
overall
cost
of
fertilizer,
and
enhance
crop
productivity.
2.3.
Herbicide
delivery
for
weed
eradication
Every
year
approximately
10–15%
the
principal
food
production
is
lost
due
to
weeds
and
other
plant
competition.
In
recent
decades,
there
has
been
an
alarming
increase
in
the
use
of
herbicides
to
man-
age
the
weeds
that
are
responsible
for
these
losses.
Each
year
47.5%
of
the
total
pesticides
that
are
used
have
been
applied
to
crops
to
manage
these
pests
[210].
The
heavy
use
of
herbicides
has
given
rise
to
serious
environmental
and
public
health
problems.
Problems
arising
from
the
herbicides
currently
in
use
are
attributed
to
their
chemical
stability,
solubility,
bioavailability,
photodegradation
and
soil
sorption.
In
addition,
transfer
of
these
agents
to
aquatic
sys-
tems
affects
water
quality,
resulting
in
adverse
impacts
to
humans,
other
biota,
and
the
wider
environment.
In
this
sense,
controlled
release
formulations
of
herbicides
have
become
a
necessity,
since
they
often
increase
herbicide
efficacy
at
reduced
doses.
Recently,
Silva
et
al.
[48]
used
alginate/chitosan
nanoparticles
as
a
carrier
sys-
tem
for
paraquat
application.
They
demonstrated
that
association
of
paraquat
with
alginate/chitosan
nanoparticles
alters
the
release
profile
of
the
herbicide,
as
well
as
its
interaction
with
the
soil,
and
hence
this
system
could
be
an
effective
means
of
reducing
negative
impacts
caused
by
paraquat.
Similarly,
Grillo
and
co-workers
[39]
prepared
and
evaluated
chitosan/tripolyphosphate
nanoparticles
as
carrier
systems
to
paraquat
herbicides.
The
results
showed
that
the
nanoparticles
were
able
to
decrease
the
herbicide
toxicity
[39].
In
another
study,
Celis
et
al.
[211]
used
bionanocomposite
mate-
rial
based
on
chitosan
and
clay
(montmorillonite)
as
an
adsorbent
for
the
herbicide
clopyralid
present
in
an
aqueous
solution
or
in
a
mixture
of
water
and
soil.
The
bionanocomposites
showed
good
herbicide
adsorption
capacity
at
pH
levels
at
which
the
anionic
form
of
the
active
principle
and
the
cationic
form
of
chitosan
predomi-
nated.
Removal
of
the
herbicide
from
aqueous
solution
was
more
effective
when
a
higher
concentration
of
chitosan
was
used
in
the
bionanocomposite.
At
slightly
acid
pH,
the
composites
effectively
adsorbed
clopyralid
from
soil.
The
use
of
this
type
of
formulation
could
help
to
limit
the
mobility
of
anionic
pesticides
in
the
environ-
ment,
reducing
risks
of
contamination
of
surface
and
subterranean
water
bodies.
Wen
et
al.
[212]
studied
the
bioavailability
of
the
chi-
ral
herbicide
dichlorprop
to
the
green
alga
Chlorella
pyrenoidosa,
in
the
absence
and
presence
of
chitosan
nanoparticles.
These
observa-
tions
provided
a
clear
indication
that
chitosan
was
able
to
modify
the
enantioselective
bioavailability
of
the
herbicide,
which
could
be
of
use
in
environmental
protection
applications.
2.4.
Micronutrient
delivery
for
crop
growth
promotion
It
is
a
well
known
fact
that
micronutrients
like
manganese,
boron,
copper,
iron,
chlorine,
molybdenum,
and
zinc
promote
opti-
mum
plant
growth.
Steady
increases
in
crop
yields
following
the
1960s
‘green
revolution’
has
progressively
depleted
the
level
of
essential
micronutrients
like
zinc,
iron
and
molybdenum
in
the
soil
[213].
Farming
practices,
such
as
liming
acid
soils,
contribute
to
micronutrient
deficiencies
in
crops
by
decreasing
the
availabil-
ity
[213].
Foliar
application
of
micronutrients
is
now
a
common
agricultural
practice
and
is
shown
to
enhance
its
uptake
by
the
leaves
[214].
Nanoformulations
of
micronutrients
may
be
used
to
spray
crops
for
enhanced
foliar
uptake,
or
nanomaterials
with
micronutrients
may
be
used
as
a
soil
addition
for
their
slow
release
to
promote
plant
growth
and
improve
soil
health
[215].
For
an
example,
Tao
et
al.
[61]
synthesized
chitosan
modified
with
1-
naphthylacetic
acid,
which
is
an
important
plant
growth
hormone.
The
results
indicated
that
the
release
of
the
1-naphthylacetic
acid
was
strongly
dependent
on
pH
and
temperature,
and
could
con-
tinue
for
55
days
at
pH
12
and
60 ◦C.
Despite
this
dependence,
the
formulation
offers
potential
for
the
slow
release
of
plant
growth
hormones.
2.5.
Soil
health
improvement
The
installation
of
nanosensors
in
farmers’
fields
is
being
applied
to
enable
the
real
time
monitoring
of
soil
conditions
and
the
early
detection
of
potential
problems
such
as
nutrient
depletion
or
insuf-
ficient
water
[216].
In
this
context,
nanosensors
can
help
to
extend
the
new
practices
of
precision
farming
by
detecting
and
rectifying
agronomic
problems
in
a
very
short
time
span.
Nanomaterials,
such
as
hydrogels
and
zeolites,
were
reported
to
be
useful
for
improving
the
water-holding
capacity
of
soil
[217]
and
to
absorb
environ-
mental
contaminants
[218].
Recently,
efforts
have
been
made
to
develop
a
nanoparticle
modified
chitosan
sensor
for
the
determina-
tion
of
heavy
metals
[42].
The
biosensor
is
based
on
the
combination
of
chitosan
cross-linked
with
glutaraldehyde
modified
with
para-
magnetic
Fe3O4.
The
!-Fe3O4/CS
nanocomposite
film,
which
can
be
easily
prepared,
exhibits
high
accumulation
ability
for
the
deter-
mination
and
removal
of
heavy
metals
(arsenic,
lead,
and
nickel)
and
‘reports’
the
process
by
an
electrical
response.
Agnihotri
et
al.
[44]
developed
a
novel
antimicrobial
chitosan–PVA-based
hydro-
gel,
which
can
behave
both
as
a
nanoreactor
and
an
immobilizing
matrix
for
silver
nanoparticles
(AgNPs)
with
promising
antibacte-
rial
applications.
2.6.
Delivery
of
genetic
material
for
plant
transformation
The
biggest
challenge
for
gene
delivery
in
agricultural
crops
is
the
plant
cell
wall.
Traditional
gene
transfer
methods
in
plants
such
as
Agrobacterium-mediated
gene
transfer,
electroporation,
PEG-mediated
gene
transfer,
particle
gun
bombardment,
etc.,
are
costly,
labor
intensive
and
cause
significant
perturbation
to
the
growth
of
cells.
In
addition,
these
methods
have
very
low
effi-
ciency
(0.01–20%
efficiency).
Nevertheless
that
has
been
relatively
successful
for
genetic
transformation
of
dicots
[219].
Hence,
there
is
interest
in
utilizing
novel
delivery
systems
for
the
develop-
ment
of
successful
transformants.
Nanotechnology
has
shown
its
value
in
the
genetic
modification
of
plants
by
introducing
new
genes
with
a
corresponding
crop
improvement.
This
system
has
significant
advantages
in
comparison
to
conventional
and
tradi-
tional
gene
transformation
tactics.
Firstly,
nanoparticle
approaches
are
applicable
to
both
monocot
and
dicot
plants,
irrespective
of

48
P.L.
Kashyap
et
al.
/
International
Journal
of
Biological
Macromolecules
77
(2015)
36–51
tissue
or
organ
type.
Secondly,
they
can
be
used
to
overcome
transgenic
silencing
via
regulating
the
DNA
copies
combined
with
nanoparticles.
Thirdly,
nanoparticles
can
be
easily
functionalized
for
further
enhancement
of
transformation
efficiency,
if
needed.
Finally,
nanoparticle-mediated
multigene
transformation
is
possi-
ble
without
involving
traditional
methods
that
require
complex
carriers.
Overall,
these
key
features
make
nanoparticles
excel-
lent
gene
carriers
for
the
genetic
engineering
of
crops.
Zinc
oxide
nanoparticles
and
carbon
nanotubes
were
both
reported
to
pen-
etrate
tomato
(Lycopersicon
esculentum)
seed
tissues
and
plant
roots,
indicating
that
new
nutrient
delivery
systems
can
be
devel-
oped
by
exploiting
the
nanoscale
porous
domains
of
the
plant
surfaces
[220].
Gene
transfer
by
bombardment
of
DNA-absorbed
on
gold
particles
has
also
been
successfully
harnessed
for
the
development
of
transgenic
plants
in
a
species-independent
man-
ner
[221].
Torney
et
al.
[8]
demonstrated
the
delivery
of
DNA
and
chemicals
through
silica
nanoparticles
internalized
in
plant
cells,
without
any
help
from
specialized
equipment.
Martin
et
al.
[222]
reported
protein
and
DNA
co-delivery
to
plant
cells
via
the
biolistic
method,
using
mesoporous
silica
nanoparticles.
The
potential
for
biodegradable
chitosan
to
be
used
in
gene
delivery
is
supported
by
its
ability
to
protonate
in
acidic
solution
and
to
form
a
complex
with
DNA
through
electrostatic
interactions
[223].
Furthermore,
some
reports
provide
evidence
that
polymer/DNA
complexes
are
more
stable
than
those
involving
cationic
lipids,
and
can
protect
DNA
from
nuclease
degradation
[224].
Chitosan/DNA
nanoparti-
cles
may
be
readily
formed
by
coacervation
between
the
positively
charged
amine
groups
on
chitosan
and
negatively
charged
phos-
phate
groups
on
DNA.
However,
the
transfection
efficiency
of
chitosan
is
low.
The
transfection
efficiency
has
been
shown
to
depend
on
the
chitosan
molecular
weight,
degree
of
deacetyla-
tion,
pH
of
the
transfecting
medium,
and
cell
type
[225].
A
pH
of
6.8–7.0
is
critical
for
transfection
[226],
and
evidence
suggests
that
DNA
complexes
formed
by
shorter
and
close
to
monodisperse
chitosan
oligomers
(24-mer)
have
more
desirable
properties
than
ultrapure
chitosan
and
are
therefore
more
attractive
as
gene
deliv-
ery
systems
than
the
conventional
high
molecular
weight
chitosans
[227].
Besides
this,
the
degree
of
chitosan
deacetylation
also
acts
as
an
important
factor
in
chitosan-DNA
nanoparticle
formulation
as
it
affects
DNA
binding,
release
and
gene
transfection
efficiency
in
vitro
and
in
vivo
[228].
RNA
interference
(RNAi)
is
a
powerful
strategy
for
post
trans-
criptional
gene
silencing
that
can
be
mediated
by
delivery
of
syn-
thetic
double
stranded
small
interfering
RNA
(siRNA).
This
process
results
in
the
degradation
of
homologous
RNA
and
thereby
causes
knockdown
of
the
specific
target
gene
[229–231].
This
method
has
emerged
as
a
recognized
strategy
to
control
insect
pests
that
feed
upon
plants
producing
double
stranded
RNA
(dsRNA).
For
effec-
tive
insect
control
the
production
of
sufficient
dsRNA
by
transgenic
plants
as
well
as
their
delivery
in
an
effective
and
non-degraded
manner
is
required,
which
in
turn
required
continuous
feeding
of
high
levels
of
dsRNA,
because
of
dsRNA
degradation
in
the
insect
gut
[232,233].
Recently,
chitosan
has
attracted
significant
attention
for
use
in
formulations
with
small
interfering
RNA
(siRNA).
Because
of
the
cationic
nature,
chitosan
can
make
complex
with
siRNA
easily
and
forms
nanoparticles.
Several
reports
indicate
the
application
of
chitosan
nanoparticle-entrapped
siRNA
as
a
carrier
for
siRNA
delivery
[234–236].
In
one
recent
study,
Zhang
et
al.
[237]
have
shown
that
chitosan
nanoaprticles
successfully
delivered
dsRNA
(against
chitin
synthase
genes)
in
stabilized
form,
to
mosquito
lar-
vae
via
feeding.
Chitosan
nanoparticles
could
prove
to
be
efficient
in
dsRNA
delivery
due
to
their
efficient
binding
with
RNA,
pro-
tection
and
the
ability
to
penetrate
through
the
cell
membrane.
These
results
clearly
indicate
that
chitosan
nanoparticles
based
siRNA
formulations
may
contribute
to
plant
pathogen
and
pest
control
while
avoiding
the
lengthy
process
of
conventional
plant
transformations.
There
are
some
mixed
results
with
regard
to
gene
delivery
via
chitosan
nanoparticles,
but
given
the
potential
advan-
tages
of
chitosan
nanoparticles
to
assist
in
the
delivery
of
genetic
material
to
design
new
and
improved
plant
genotypes,
chitosan
will
continue
to
be
an
important
research
topic.
And,
there
is
a
real
potenital
to
use
DNA-coated
chitosan
nanoparticles
as
a
nanocar-
rier
in
a
gene
gun
system,
for
bombardment
of
plant
cells
and
tis-
sues
to
achieve
efficient
and
targeted
gene
transfer,
in
near
future.
3.
Conclusions
Application
of
chitosan
based
nanoparticles
in
agriculture
is
still
in
a
nascent
stage.
Encouraging
and
promising
results
are
already
being
achieved
in
delivery
of
agrochemicals
and
genes
for
plant
transformation
using
chitosan
nanoparticles.
The
use
of
such
nanomaterials
for
the
delivery
of
pesticides,
micronutri-
ents
and
fertilizers
is
expected
to
reduce
the
required
dosage
for
efficacy
and
ensure
a
controlled
delivery.
An
important
advance
will
have
been
realized
once
the
application
of
nanoparticles
is
able
to
deliver
biocontrol
materials
and
control
the
release
at
an
appropriate
rate
for
effective
crop
protection
and
nutrition,
and
do
so
with
a
reduced
environmental
hazard.
In
the
context
of
host–pathogen
interactions,
application
of
nanoparticle
technology
and
efficient
transportation
of
substances,
such
as
systemic
plant
defence
activators
(e.g.
salicylic
acid,
jasmonic
acid
and
benzothia-
diazole,
etc.),
to
specific
target
sites
provide
novel
solutions
for
crop
stress
alleviation.
If
it
is
possible
to
have
a
distribution
of
properly
functionalized
nanoparticles
throughout
the
plant
vascular
system
and
direct
them
to
targeted
sites,
then
these
nanoformulations
can
be
successfully
used
to
deliver
chemicals
(fungicides,
herbicides
and
insecticides,
etc.),
or
other
substances
(plant
hormones,
elic-
itors
and
nucleic
acids)
into
localized
areas
of
plant
tissues.
This
could
help
to
decode
ever
–
unveil
insight
story
at
physiological,
biochemical
and
genetic
levels,
ultimately
helping
to
make
sus-
tainable
agriculture
a
reality.
The
foundations
of
new
crop
health
techniques
have
been
laid,
and
research
into
many
of
the
poten-
tial
applications
is
ongoing,
especially
in
the
field
of
crop
genetic
engineering
and
production
of
selective,
effective
and
low
dose
plant
protection
products
using
chitosan-nanoparticle
as
a
prin-
ciple.
However,
issues
such
as
increasing
the
scale
of
production
processes
and
lowering
costs,
as
well
as
toxicological
perspectives,
still
must
be
addressed
to
further
advance
nanotechnology
into
sustainable
agriculture.
While
research
interest
into
chitosan
nanoparticle
based
deliv-
ery
systems
is
increasing,
the
current
level
of
knowledge
does
not
allow
a
fair
assessment
of
the
pros
and
cons
that
will
arise
from
the
use
of
chitosan
based
nano-pesticides
in
agriculture.
As
a
pre-
requisite
for
such
assessment,
a
better
understanding
of
the
fate
and
effect
of
such
products
after
their
application
is
required.
The
suitability
of
current
regulations
should
also
be
analyzed
so
that
refinements
can
be
implemented,
if
needed.
Another
major
hurdle
in
sustainable
agriculture
is
the
removal
of
harmful
contaminants
from
soil.
This
is
another
area
where
it
is
believed
that
unique
properties
of
chitosan
nanoparticles
may
prove
to
be
useful,
in
envi-
ronmental
detection,
sensing
and
remediation
systems.
Overall,
it
can
be
concluded
that
chitosan
nanoparticles
based
technology
have
a
promising
future
with
value
in
crop
productivity
in
sustained
and
eco-friendly
ways.
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