Green Synthesis of Fluorescent Carbon Dots for Selective Detection of Tartrazine in Food Samples

Abstract

A simple, economical, and green method for the preparation of water-soluble, high-fluorescent carbon quantum dots (C-dots) has been developed via hydrothermal process using aloe as a carbon source. The synthesized C-dots were characterized by atomic force microscope (AFM), transmission electron microscopy (TEM), fluorescence spectrophotometer, UV-vis absorption spectra as well as fourier transform infrared spectroscopy (FTIR). The results reveal that the as-prepared C-dots were spherical shape with an average diameter of 5 nm and emit bright yellow photoluminescence (PL) with a quantum yield of approximately 10.37%. The surface of the C-dots was rich in hydroxyl groups and presented various merits including high fluorescent quantum yield, excellent photostability, low toxicity and satisfactory solubility. Additionally, we found that one of the widely-used synthetic food colorants, tartrazine, could result in a strong fluorescence quenching of the C-dots through a static quenching process. The decrease of fluorescence intensity made it possible to determine tartrazine in the linear range extending from 0.25 to 32.50 μM, This observation was further successfully applied for the determination of tartrazine in food samples collected from local markets, suggesting its great potential towards food routine analysis. Results from our study may shed light on the production of fluorescent and biocompatible nanocarbons due to our simple and environmental benign strategy to synthesize C-dots in which aloe was used as a carbon source.

Full text

Green Synthesis of Fluorescent Carbon Dots for Selective Detection
of Tartrazine in Food Samples
Hua Xu,
†
Xiupei Yang,*
,†
Gu Li,
†
Chuan Zhao,
†
and Xiangjun Liao*
,§
†
College of Chemistry and Chemical Engineering, China West Normal University, Nanchong 637000, People’s Republic of China
§
Exposure and Biomonitoring Division, Health Canada, 50 Colombine Driveway, Ottawa K1A 0K9, Canada
*
SSupporting Information
ABSTRACT: A simple, economical, and green method for the preparation of water-soluble, high-fluorescent carbon quantum
dots (C-dots) has been developed via hydrothermal process using aloe as a carbon source. The synthesized C-dots were
characterized by atomic force microscope (AFM), transmission electron microscopy (TEM), fluorescence spectrophotometer,
UV−vis absorption spectra as well as Fourier transform infrared spectroscopy (FTIR). The results reveal that the as-prepared C-
dots were spherical shape with an average diameter of 5 nm and emit bright yellow photoluminescence (PL) with a quantum
yield of approximately 10.37%. The surface of the C-dots was rich in hydroxyl groups and presented various merits including high
fluorescent quantum yield, excellent photostability, low toxicity and satisfactory solubility. Additionally, we found that one of the
widely used synthetic food colorants, tartrazine, could result in a strong fluorescence quenching of the C-dots through a static
quenching process. The decrease of fluorescence intensity made it possible to determine tartrazine in the linear range extending
from 0.25 to 32.50 μM, This observation was further successfully applied for the determination of tartrazine in food samples
collected from local markets, suggesting its great potential toward food routine analysis. Results from our study may shed light on
the production of fluorescent and biocompatible nanocarbons due to our simple and environmental benign strategy to synthesize
C-dots in which aloe was used as a carbon source.
KEYWORDS: carbon quantum dots, tartrazine, aloe, fluorescence quench
■INTRODUCTION
Tartrazine is a widely used synthetic food colorant that can be
found in certain food products such as candies, beverages,
bakery products, and dairy products.
1,2
However, some studies
have revealed that tartrazine may cause adverse health effects
such as changes in hepatic and renal parameters and
reproductive toxicity, as well as neurobehavioral poisonousness
when it is excessively consumed.
3,4
Therefore, the food industry
must strictly control and regulate the content of tartrazine in
foods, which necessitates an interest in the development of an
efficient measurement technique to determine tartrazine in
foods in terms of rapidity, simplicity, and sensitivity.
Until now, various instrumental techniques that analyzed
tartrazine in foodstuffproducts have been increasingly
employed, which include thin-layer chromatography (TLC)
method,
5
electrochemical sensor,
6
spectrophotometry,
7
and
high-performance liquid chromatography (HPLC).
8
Never-
theless, these methods may not be suitable for routine
monitoring because they require sophisticated equipment and
time-consuming sample preparation. As a result, the develop-
ment of a simple, economical, fast, and reliable assay of
tartrazine has been a challenge for analytical researchers.
Recently, carbon quantum dots (C-dots), which are a new
class of fluorescent nanomaterials with a size of <10 nm, have
received much attention owing to their good water solubility,
excellent photostability, low toxicity, and favorable biocompat-
ibility.
9,10
The application of C-dots has been explored in
fluorescent biosensing and in vivo bioimaging and food
detection together with food-packaging domain.
11−13
C-Dots
also served as reasonable candidates for future nanodevices,
cellular imaging, and biomedicine.
14,15
Over the past years,
several methods have been developed for the synthesis of C-
dots, including arc discharge,
16
laser ablation,
17,18
electro-
chemical oxidation,
19
and microwave irradiation.
20
However,
hydrothermal carbonization has provided great advancement
over existing physical methods, which is due to its simplicity
and production of C-dots with good quantum yield. Recently,
hydrothermal carbonization of chitosan, orange peels, coffee
grounds, and grass has been successfully applied to synthesize
fluorescent C-dots, which could be probes for recognizing
various chemical species and cells in vitro and in vivo.
21−24
All
of these proved that hydrothermal carbonization is an eco-
friendly, facile, and classical route for the synthesis of C-dots in
aqueous media. From the point of material preparation, there is
an urgent need to locate new carbon sources for simple,
economical, and green synthesis of C-dots.
In this work, a facile and green method for the preparation of
fluorescent C-dots by hydrothermal treatment of aloe and the
application has been proposed. On the basis of fluorescence
quenching, the prepared C-dots can serve as an effective sensor
for sensitive and selective determination of tartrazine. The use
of the synthesized C-dots for detection has been validated by
measuring the concentration of tartrazine in food samples
collected from a local supermarket.
Received: May 8, 2015
Revised: July 8, 2015
Accepted: July 8, 2015
Published: July 8, 2015
Article
pubs.acs.org/JAFC
© 2015 American Chemical Society 6707 DOI: 10.1021/acs.jafc.5b02319
J. Agric. Food Chem. 2015, 63, 6707−6714
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■EXPERIMENTAL PROCEDURES
Materials. Aloe was obtained from potted plants in our laboratory
and washed with water for further use. Dichloromethane (CH2Cl2,
99.5%) was purchased from Aladdin Industrial Corp. (Shanghai,
China). Tartrazine (C16H9N4Na3O9S2, 87%), sunset yellow
(C16H10N2Na2O7S2, 85%), erioglaucine disodium salt
(C37H34Na2N2O9S3, 85%), and amaranth (C20H11N2Na3O10S3, 85%)
were received from Aladdin Chemistry Co. Ltd. (Shanghai, China).
Sodium dihydrogen phosphate (NaH2PO4·H2O) and disodium
hydrogen phosphate dodecahydrate (Na2HPO4·12H2O) were ob-
tained from Tianjin Fuchen Chemical Reagents Co., Ltd. (Tianjin,
China). All chemicals were of analytical reagent grade and used
without further purification. The ultrapure water used throughout the
experiments was purifiedthroughanUPH-II-20Tupwater
purification system (Chengdu Ultrapure Technology Co. Ltd.,
Chengdu, China).
Apparatus and Characterization. The AFM analysis was carried
out on a Multimode/Nanoscope (Veeco Corp., USA) on a tapping
mode with a RTESP-Veeco cantilever on a platinum-coated mica
substrate. All absorption spectra were recorded on a Shimadzu UV-
2550 UV−vis absorption spectrophotometer (Kyoto, Japan). Fluo-
rescence measurements were conductedwithaCaryEclipse
fluorescence spectrophotometer (Varian, Palo Alto, CA, USA). The
infrared spectra were obtained on a Nicolet 6700 Fourier transform
infrared (FTIR) spectrometer (Thermo Electron Corp., USA) with
passed KBr pellet at room temperature.
Synthesis of Fluorescent C-Dots. The C-dots were prepared by
hydrothermal treatment of fresh aloe in water. In a typical procedure, 5
g of aloe was added into 25 mL of water, and then the mixture was
transferred into a 50 mL Teflon-lined autoclave and was heated at 180
°C for 11 h. After heating, the autoclaves were allowed to naturally
cool in a fume hood on a heat-resistant plate and the resulting yellow
solution was filtered with a 0.22 μm membrane followed by washing
with dichloromethane to remove the unreacted organic moieties.
Finally, the upper light yellow aqueous solution containing C-dots was
collected and stored at 4 °C for further characterization and use.
Quantum Yield Measurements. The quantum yield of the as-
synthesized C-dots was measured on the basis of a procedure
described previously.
25
Rhodamine 6G aqueous solution was used as a
reference standard, for which the quantum yield was 0.95 at 488 nm
reported by the literature. Absolute values of the quantum yield were
calculated according to the equation
η
η
Φ=Φ
I
A
A
I
x
x
x
xstd std
std
2
std
2
where Φis the quantum yield of the as-prepared C-dots, Ais the
absorbance, Iis the corrected emission intensity at the excitation
wavelength, and ηis the refractive index of the solvent. The subscripts
“std”and “x”refer to reference standard with known quantum yield
and the C-dots solution, respectively. For the sake of reducing effects
of reabsorption within the sample on the observed emission spectrum,
the absorbance values (A) of all solutions in the 10 mm cuvette were
always controlled under 0.1.
Sample Pretreatment. Candy, steamed buns made of corn, and
honey were selected as test samples because tartrazine may be added
as a colorant into them. All samples were obtained from a local
supermarket in Nanchong, China. The candy or honey sample (10.0
g) was crushed and subsequently dissolved in hot water (∼60 °C).
The resulting solution was transferred and diluted to a 50 mL
volumetric flask. The diluted solution was filtered through a 0.45 μm
filter membrane for subsequent use. Ten grams of steamed buns and a
certain amount of water were added into a 100 mL beaker, and then
the mixture was blended by electric mixer and extracted with ultrasonic
for 15 min, respectively. After extraction, the mixture was centrifuged
at 12000 rpm for 10 min followed by transferring the supernatant and
diluting to 50 mL. The diluted solution was also filtered through a 0.45
μmfilter membrane for subsequent use. The above sample
pretreatment method is referenced to the literature with some
minor modifications.
26
Detection of Tartrazine in Food Samples. The tartrazine
detection procedure was carried out in phosphate buffer (PB) (30
mM, pH 6.0) at 5 °C. In a typical run, 450 μL of C-dots solution was
added into 500 μL of PB, followed by the addition of 1000 μLof
sample solution and thorough mixing. The resulting mixture was
reconstituted to 4 mL with water. After a reaction time of 5 min at 5
°C, the spectra were recorded under excitation at 441 nm with slit
widths setting at 10/10 nm. All of the recoveries were calculated
according to the equation below:
=−CCCrecovery ( )/
measured initial adde
d
■RESULTS AND DISCUSSION
Optimization of the Synthesis Conditions. To ensure
excellent performance of the synthesized C-dots, we have
optimized the time and temperature of the synthesis simply,
and results are shown in Figures S1 and S2. From Figure S1 we
can see clearly that the fluorescence intensity gradually
increased with the reaction time up to 11 h but decreased
when the time exceeded 11 h. Therefore, 11 h was chosen as
the optimal reaction time. Simultaneously, as displayed in
Figure S2, the fluorescence intensity increased with the reaction
temperature rise. We finally chose 180 °C as the optimal
temperature because when the temperature exceeded 180 °C,
the fluorescence intensity increase was not obvious.
Characterization. Figure 1 shows the typical AFM image of
the as-synthesized C-dots solution. It reveals that the C-dots are
well dispersed in solution with spherical shape and have an
average size of 5 nm approximately. Similarly, Figure S3 shows
the typical TEM image of the C-dots. It can be seen that the C-
Figure 1. AFM images of the C-dots.
Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
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dots are in the monodispersion state and their size is consistent
with the results of AFM.
The absorption (black line) and emission spectra (green
line) of the as-synthesized C-dots are shown in Figure 2. A peak
at 278 nm is exhibited in the UV−vis absorption spectrum,
which was attributed to n−π*transition of CO and π−π*
transition of CC.
27
The photoluminescent (PL) spectrum
shows an optimal emission peak at about 503 nm when excited
at 441 nm. The inset photograph in Figure 2 indicates the C-
dots aqueous solution under visible (a) and UV illumination at
365 nm (b). The bright yellow PL of the C-dots under UV light
is strong enough to be seen with the naked eye, but when
tartrazine was added, the fluorescence was obviously quenched
(c). The full width at half-maximum (fwhm) is 100 nm,
suggesting a relatively small size distribution of C-dots, which
was consistent with AFM and TEM data and approximately
equal to that of most reported C-dots.
28,29
The strong
fluorescence can be caused by the surface energy traps in the
C-dots that become emissive upon stabilization.
17
To further investigate the optical properties, the PL emission
spectrum of the C-dots was recorded at progressively increasing
excitation wavelengths (Figure 3). It can be observed that a red
shift was attributed in the emission spectra of C-dots from 443
to 525 nm with increasing excitation wavelengths, accompanied
by a decrease of the fluorescence intensity, revealing that the
fluorescence of C-dots is strongly dependent on the excitation
wavelength. This finding is substantially in agreement with that
of Vaibhavkumar.
30,31
To investigate the components, surface
groups, and structure of the as-synthesized C-dots, EDS and
FT-IR have been carried out. Figure S4 shows the as-prepared
C-dots are mainly composed of C, H, O, and N. As shown in
Figure 4, characteristic absorption bands of the −OH stretching
vibration mode at about 3400 and 1073 cm−1could be
observed. The band at 2923 cm−1corresponds to the C−H
stretching mode.
32
In addition, the peaks appearing at 1590 and
1400 cm−1may be caused by the asymmetric and symmetric
stretching vibration of COO−, respectively. These findings
provide evidence that both the hydroxyl and carboxylic groups
originated from carbohydrates in the aloe.
It is well-known that the photostability of C-dots plays a key
role in sensitive fluorescence detection. In this connection, we
studied the emission behavior of the C-dots under continuous
UV light illumination at 365 nm for 120 min. It was also noted
that as shown in Figure S5 the photobleaching of C-dots is not
observed and the fluorescence intensity of C-dots remained
constant even after 120 min of continuous UV light
illumination, indicating the good photostability of C-dots.
Using rhodamine 6G as a reference, a PL quantum yield (QY)
of 10.37% was measured. Table S1 shows the comparison of
the optical properties and applications of the C-dots derived
from aloe with the reported methods. It can be seen that the
present method is green and simple and has a relatively high
quantum yield. At the same time, it is worth mentioning that
the as-prepared C-dots emit strong yellow fluorescence,
whereas most reported carbon dots are blue, and they can be
a sensitive fluorescent probe for colorant detention.
Design Principle of the Sensor. Under the same
experimental conditions, the fluorescence spectra of the C-
dots alone and the system of C-dots with tartrazine were
recorded, respectively. As shown in Figure S6, the C-dots
presented strong fluorescence at 503 nm when excited at 441
Figure 2. UV−vis absorption (black line) and fluorescence emission
(green line) spectra of the C-dots. (Inset) Photographic images of C-
dots under (a) visible light, (b) ultraviolet light, and (c) ultraviolet
light with tartrazine (22.5 μM).
Figure 3. Fluorescence emission spectra of C-dots obtained at
different excitation wavelengths progressively increasing from 370 to
480 nm in 10 nm increments.
Figure 4. FT-IR spectrum of C-dots.
Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
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nm. Upon the addition of tartrazine, the fluorescence intensity
of the prepared C-dots decreased significantly. On the basis of
the fluorescence quenching, we speculated that a facile
fluorescence sensor for the determination of tartrazine could
be constructed. The synthetic strategy for C-dots and the
principle of tartrazine sensing are schematically presented in
Scheme 1.
Mechanism of Fluorescence Quenching. Broadly speak-
ing, various kinds of molecular interactions with the quencher
molecule can reduce the fluorescence quantum yield, such as
electron or energy transfer, collisional quenching, excited-state
reaction, and ground-state complex formation The quenching
mechanisms are usually divided into dynamic quenching, which
results from collision, and static quenching, resulting from the
formation of a ground-state complex between the fluorescence
material and quencher. On the other hand, they could be
distinguished by some additional formations such as the
relationship between the quenching and viscosity, temperature,
and lifetime measurements.
33
In general, the dynamic
fluorescence quenching constants will increase with the rise
of the system temperature due to the energy transfer efficiency,
and the effective collision times between molecules will also
increase. On the contrary, the values of the static fluorescence
quenching constants will decrease with the rise of temperature.
Let us suppose that the mechanism is dynamic quenching; it
can be described by the Stern−Volmer equation
34
τ=+ =+FF K K/ 1 [Q] 1 [Q]
0SV q0
where F0and Fare the C-dots fluorescence intensities at 503
nm in the absence and presence of tartrazine, respectively; KSV
and Kqare the Stern−Volmer quenching constant and the
bimolecular quenching constant, respectively; [Q] is the
concentration of tartrazine; and τ0is the average lifetime of
the C-dots without any other fluorescence quencher, with a
general value of 10−8s. Figure 5 shows the fluorescence
intensities of the C-dots analyzed by plotting F0/Fversus [Q]
at 278, 288, 298, and 308 K. Table 1 summarizes the calculated
KSV and Kqvalues for each temperature. As shown, the KSV is
inversely correlated with temperature, and the value of Kqis far
larger than 2.0 ×1010 L mol−1s−1, which is the maximum
scatter collision quenching constant. These findings indicate
that the quenching process may be caused by static quenching.
Additionally, the UV−vis spectra of the prepared C-dots alone
and the system of the C-dots with tartrazine are illustrated in
Figure S7. As can be seen from this figure, with the addition of
tartrazine, the absorbance intensity of the C-dots at 280 nm
increases, with a blue shift. This observation indicates that the
formation of ground-state complexes is generated due to the
interaction between tartrazine and C-dots.
Optimization of Experimental Conditions. With the
purpose of investigating the sensitivity, precision, and selectivity
of the analytical method, parameters including the medium pH,
dosage of C-dots, reaction temperature, and incubation time
were systematically optimized for the system.
The effect of the solution pH on the fluorescence quenching
of C-dots in the presence of tartrazine is shown in Figure 6a. An
increase in pH from 4.0 to 6.0 results in the increased
fluorescence quenching efficiency (represented as F0/F, where
F0and Fare the fluorescence intensities of the C-dots at 503
nm before and after the addition of tartrazine, respectively.)
whereas a further increase in pH from 6 to 7.5 leads to a
gradual decrease. Such an observation suggests that the
fluorescence intensity of the C-dots strongly depends on the
pH value of the system. Our results are consistent with those of
C-dots functioned with hydroxyl and carboxylic/carbonyl
moieties.
10,19,32
Consequently, we selected 6.0 as the optimal
pH for our study.
The effect of the dosage of C-dots on the fluorescence
quenching efficiency is presented in Figure 6b. The
fluorescence quenching efficiency gradually increased with the
dosage of C-dots up to 450 μL. When the dosage of C-dots
Scheme 1. Scheme of the Synthetic Strategy for C-Dots and the Principle of Tartrazine Sensing
Figure 5. Stern−Volmer plots for the system of C-dots−tartrazine
under temperatures of 278, 288, 298, and 308 K, respectively. F0and F
are the fluorescence intensity of C-dots in the absence and presence of
tartrazine, respectively. Conditions: C-dots, 450 μL; PB, 30 mM, pH
6.0.
Table 1. Stern−Volmer Quenching Constants for the
Interaction of C-Dots and Tartrazine at Different
Temperatures
pH T(K) KSV (L mol−1)Kq(L mol−1s−1)RSD
6.0 278 5.663 ×1045.663 ×1012 0.9984 0.0278
6.0 288 5.213 ×1045.213 ×1012 0.9960 0.0402
6.0 298 5.178 ×1045.178 ×1012 0.9967 0.0361
6.0 308 4.734 ×1044.734 ×1012 0.9939 0.0452
Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
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exceeded 450 μL, the fluorescence quenching efficiency
decreased. Therefore, 450 μL was used as the optimal dosage
for further performance
Figure 6c shows the fluorescence curves of the system at
different temperatures. As the temperature increased from 5 to
35 °C, the fluorescence quenching efficiency decreased
gradually. Among the temperatures studied, the maximum
fluorescence intensity efficiency was achived at 5 °C. Hence, 5
°C is selected as the optimum reaction temperature.
The effect of incubation time on the fluorescence intensity of
the system is shown in Figure 6d. No significant changes in F0/
Fwere observed after an incubation time of 1 min. To ensure
the consistency of the whole experiment, it is important to
record the stable fluorescence signal. Thus, 5 min is
conservatively chosen as the optimum incubation time.
Analytical Performance for Tartrazine Sensing.
Sensitivity. The dependence of F0/Fon the different
concentrations of tartrazine under the identical conditions is
shown in Figure 7. As displayed, the fluorescence quenching
efficiency of C-dots gradually decreases with an increase in the
concentration of tartrazine. As shown in the upper right inset of
Figure 7, the decrease in fluorescence quenching efficiency
exhibited a linear response to the tartrazine concentration in
the range of 0.25−32.50 μM, which was consistent with the
photograph of the solutions under UV light. The calibration
curve can be depicted as F0/F= 0.9604 + 0.0577X(Xis the
concentration of tartrazine, μM) with a correlation coefficient
of 0.9986. The relative standard deviation (RSD) was 0.25%
through five parallel determinations (n=5)atafixed tartrazine
concentration of 10.00 μM, indicating the excellent reliability of
this sensor. The detection limit is estimated to be 73 nM at a
signal-to-noise ratio of 3.
In Table 2, we compare the experimental results with those
for reported methods of tartrazine detection. As shown in Table
2, our developed assay exhibits a wider linear range and lower
RSD compared to some methods. Our method can be an
alternative to others for the determination of tartrazine in
samples, although the limit of detection (LOD) our method is
not the smallest in Table 2. It is worth mentioning that almost
all of the reported sensors need special equipment, a
sophisticated technique, or complicated operations. By contrast,
the sensor we developed here has its own features, including
low instrumentation cost, simplicity of operation, and fast
Figure 6. Effect of (a) pH of buffer solution, (b) dosage of C-dots, (c) reaction temperature, and (d) reaction time on fluorescence quenching
efficiency of the C-dots−tartrazine system. F0and Fare the fluorescence intensity of C-dots in the absence and presence of tartrazine, respectively.
Conditions: PB, 30 mM; tartrazine, 10 μM.
Journal of Agricultural and Food Chemistry Article
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response, which makes it more applicable for routine analysis of
tartrazine in foods.
Selectivity. To evaluate the selectivity of this sensing system,
we examined the fluorescence response of the system to
tartrazine at a concentration of 5.0 μM with the presence of
coexisting foreign substances such as K+,Ca
2+,Zn
2+,Fe
3+,
HCO3
‑,NO
2
‑, glutamic acid, glutathione (GSH), citric acid,
phenylalanine, starch, tartaric acid, vitamin C, glucose, lactose,
sunset yellow, erioglaucine disodium salt, and amaranth under
the same conditions. As shown in Figure 8, for the present
study, various different substances were added in the test
solution at the amount of 100 times tartrazine initially, and the
ratio would be gradually reduced when the interference
presented. It was found that some of the materials, such as
Fe3+, sunset yellow, erioglaucine disodium salt, and amaranth,
could be only allowed at relatively lower levels. Nevertheless,
the concentrations of these substances were much lower than
the allowed levels in food samples. Meanwhile, most of the
common excipients in foods could be tolerated at high
concentrations up to 100 times. That is to say the established
strategy possesses a high selectivity toward tartrazine detection.
Application in Food Samples. The developed approach was
employed to detect the trace level of tartrazine in some food
samples. The results for the pretreated food samples spiked
with known amounts of standard tartrazine are shown in Table
3. The intraday and interday recoveries ranged from 88.6 to
103.4% and from 87.3 to 106.6%, respectively. All of these
results indicate that the accuracy and reliability of the proposed
method can be applied to the determination of tartrazine in
food samples.
In summary, C-dots based on aloe were synthesized via a
simple and green method. Without further chemical
modification, the synthesized C-dots have been applied to the
sensitive and selective detection of tartrazine in some food
samples. The new C-dots described here may extend their great
potential for cell imaging and drug delivery applications due to
Figure 7. Fluorescence emission spectra of C-dots in the presence of
different concentrations of tartrazine in 30 mM PB (pH 6.0). From a
to l: 0.00, 0.25, 0.75, 2.50, 3.75, 5.00, 7.50, 12.50, 17.50, 22.50, 27.50,
32.50 μM, respectively. C-dots, 450 μL. (Inset) Photographic images
of the corresponding solutions under UV light and the relationship
curve between F0/Fand concentration of tartrazine.
Table 2. Comparison of the Proposed Method with Other Methods for Determination of Tartrazine
method linear range (μM) R2LOD (nM) RSD% ref
graphene and mesoporous TiO2electrochemical sensor 0.02−1.18 0.994 8 2.70 26
spectrophotometry method 0.00131−0.67 0.992 0.56 0.98 23
electrochemical detection 0.11−56 56 3.12 17
electrochemical detection 0.05−20 14.3 18
electrochemical sensor 0.00936−0.37 0.994 2.8 4.3 22
high-performance liquid chromatography 0.0934−9.34 0.999 18.5 4.3 35
alumina microfibers-based electrochemical sensor 0.005−0.14 0.998 2.0 4.7 36
gold nanoparticles carbon paste electrode 0.05−1.6 0.997 2 1.1 37
differential pulse polarography 0.19−19 0.999 30 38
multiwalled carbon nanotubes film-modified electrode 0.37−74.8 0.990 187 5.2 39
solid phase spectrophotometry 0.094−1.22 0.998 4.00 40
capillary zone electrophoresis 5.6−178 0.995 2430 41
thin-layer chromatography 74.9−356 0.992 0.03 5
reversed-phase high-performance liquid chromatography 0.011−39.3 0.999 3.5 42
fluorescence analysis 0.25−32.5 0.998 73 0.25 this work
Figure 8. Effects of potentially interfering substances: (0) non-
interference; (1) glucose, 500 μM; (2) lactose, 500 μM; (3) starch,
500 μM; (4) citric acid, 500 μM; (5) tartaric acid, 500 μM; (6)
ascorbic acid, 500 μM; (7) glutamic acid, 250 μM; (8) phenylalmine,
250 μM; (9) NO2
−, 500 μM; (10) HCO3
‑, 500 μM; (11) Ca2+, 500
μM; (12) Zn2+, 500 μM; (13) K+, 500 μM; (14) Fe3+,25μM; (15)
sunset yellow, 5.0 μM; (16) erioglaucine disodium salt, 25 μM; (17)
amaranth, 5.0 μM. Conditions: C-dots, 450 μL; PB, 30 mM, pH 6.0;
tartrazine, 5.0 μM.
Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
J. Agric. Food Chem. 2015, 63, 6707−6714
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the simplicity of their synthesis procedure and the use of
affordable and environmentally friendly aloe as carbon source.
■ASSOCIATED CONTENT
*
SSupporting Information
Experimental procedures for EDS, supplementary figures of
EDS, fluorescence spectra, and absorbance spectra of the C-
dots and the system of C-dots−tartrazine. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.jafc.5b02319.
■AUTHOR INFORMATION
Corresponding Authors
*(X.Y.) Phone/fax: +86-817-2568081. E-mail: xiupeiyang@
163.com.
*(X.L.) Phone/fax: (613) 415-2098. E-mail: xiangjun.liao@
mail.mcgill.ca.
Funding
We thank the Natural Science Foundation of China
(21277109) and the Program for Young Scientificand
Technological Innovative Research Team in Sichuan Province
(2014TD0020) for research grants.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
We thank Prof. Martin M. F. Choi of the Department of
Chemistry, Hong Kong Baptist University, for valuable
suggestions and fluorescence spectra study.
■ABBREVIATIONS USED
C-dots, carbon quantum dots; TEM, transmission electron
microscopy; AFM, atomic force microscope; FTIR, Fourier
transform infrared spectroscopy; EDS, energy dispersive
spectrometry; TLC, thin-layer chromatography; HPLC, high
performance liquid chromatograph; fwhm, full width at half-
maximum; PB, phosphate buffer; PL, photoluminescent; QY,
quantum yield; LOD, limit of detection; RSD, relative standard
deviation; GSH, glutathione
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Value = mean ±SD (n= 5).
b
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Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
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Journal of Agricultural and Food Chemistry Article
DOI: 10.1021/acs.jafc.5b02319
J. Agric. Food Chem. 2015, 63, 6707−6714
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