Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx

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A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultra-trace chlortoluron in water Huilin Tao ⇑, Xiufen Liao, Chao Sun, Xiangli Xie, Fuxin Zhong, Zhongsheng Yi, Yipeng Huang Guangxi Scientific Experiment Center of Mining, Metallurgy and Environment, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin 541004, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 A novel FRET system was constructed

base on high quantum yielding water-soluble CDs as donor, and CdTe QDs as acceptor.  FRET system was used for the analysis of chlortoluron for the first time.  The effect of critical parameters for the detection were studied in detail.  The FRET platform was developed with high sensitive and selective.

a r t i c l e

i n f o

Article history: Received 9 April 2014 Received in revised form 18 September 2014 Accepted 9 October 2014 Available online xxxx Keywords: Carbon dots CdTe quantum dots Fluorescence resonance energy transfer Chlortoluron

a b s t r a c t In this paper, a fluorescence resonance energy transfer (FRET) system between fluorescence carbon dots (CDs, donor) and CdTe quantum dots (CdTe, acceptor) was constructed, and a novel platform for sensitive and selective determination of chlortoluron was accordingly proposed. It was found that in Tris–HCl buffer solution at pH = 8.7, energy transfer from CDs to CdTe occurred, which resulted in a great enhancement of the fluorescence intensity of CdTe. Upon the addition of chlortoluron, in terms of strong interaction between chlortoluron and CdTe QDs through the formation of chlortoluron–CdTe ground state complex, resulted in CdTe fluorescence quenching. Under optimal conditions, in range of 2.4  1010 mol L1–8.5  108 mol L1, the change of CdTe fluorescence intensity was in good linear relationship with the chlortoluron concentration, and the detection limit was 7.8  1011 mol L1 (S/ N = 3). Most of common relevant substance, cations and anions did not interfere with the detection of chlortoluron. The proposed method was applied to determine chlortoluron in water samples with satisfactory results. Published by Elsevier B.V.

Introduction In early 1950s, the phenylurea herbicides were first adopted in cultivated fields to control weed growth. Chlortoluron, as a selective herbicide of phenylurea family derivatives, is one of the most widely used herbicides with high efficiency to control annual grasses and ⇑ Corresponding author. Tel.: +86 773 589 8551; fax: +86 773 589 6839. E-mail address: [email protected] (H. Tao).

broad-leaved weeds (the chemical structure of chlortoluron was shown in Fig. 1). During the chronic exposition, chlortoluron shows a carcinogenic properties, and it is directly poisonous to aquatic organisms. Chlortoluron has frequently been detected in surface and ground water with content from 9.4  1010 mol L1 to 5.7  109 mol L1 [1], even though its solubility is low in water. Previously described platform for its analysis involves chromatographic [2–4], electrochemical [5–7], and enzyme-linked immunosorbent assay [8,9]. Though the above methods show some

http://dx.doi.org/10.1016/j.saa.2014.10.020 1386-1425/Published by Elsevier B.V.

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

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advantages, they have some limits in real sample monitoring, because these methods usually urge relative expensive instruments and complicated procedures. Thus, the development of new methods for the simple, rapid, sensitive and selective quantification chlortoluron is a challenging task and one of considerable interests. Fluorescence resonance energy transfer (FRET) is a kind of nonradiative energy transferring from an excited donor to an acceptor molecule through a long-range dipole–dipole interaction [10]. FRET has become an attractive method in various analytical strategies [10–14], as a result of the inherent sensitivity and simple equipment. Fluorescent carbon dots (CDs) possess unique optoelectronic properties: broad absorption spectra, size-tunable photoluminescence (PL), long PL lifetimes, and high quantum yields, and it has been widely used in analysis of pollutants, virus, biomacromolecule, metal ions [15–18] and so on. Thus, it can be used as an excellent fluorescent acceptor or donor to construct more efficiency FRET strategy. While fluorescent CDs used in FRET strategy were rarely studied. In this paper, therefore, we have made previous effort to construct a novel FRET strategy in determination of chlortoluron based on CDs treated as energy donors, and CdTe treated as energy acceptor. The simple detection strategy is presented in Scheme 1, energy transfer from CDs to CdTe results in the fluorescence quenched of CDs and fluorescence enhanced of CdTe. The introduction of chlortoluron led to the quench of CdTe fluorescence intensity, due to the formation of ground state complex. The fluorescence is quenched proportionally to the concentration of chlortoluron. The sensitivity and selectivity of this CDs–CdTe FRET system for chlortoluron detection were also evaluated. The energy transfer mechanism was studied in detail, some important factors which would affect the efficiency of FRET system also been optimized. Methods and materials

Synthesis of fluorescence CDs In order to obtain homogeneous solution, the pristine CDs were synthesized from sodium citrate through a simple, convenient and one-step hydrothermal method according to the literature [18]. In brief, 0.2 g sodium citrate, 1.5 g NH4HCO3 and 10 mL DDW were put into a Teflon-equipped stainless steel autoclave respectively. Successively, the mixture was hydrothermal treatment for 4 h at 180 °C in a drying oven. After reaction finished, the autoclave was cooled to room temperature. For purification, the product was conducted through a dialysis tube (1000 Da, molecular weight cutoff) in dark for about 24 h, and the purified homogeneous CDs were thus obtained, which was stable for several months. The final product was re-dissolved to 100 mL in DDW and store in 4 °C. Preparation of thioglycolic acid-modified water-soluble CdTe The thioglycolic acid (TGA)-modified water-soluble CdTe were prepared according to the method described previously [19] with slightly modified. In a three-necked flask (25 mL), 0.048 g of tellurium powder (Te), 5 mL of DDW and 0.120 g NaBH4 was added and vigorous stirred under nitrogen until NaBH4 was completely dissolved. After that, the mixture was heated to 65 °C until the black Te powder was changed to violet transparent solution. Fresh NaHTe was thus obtained. The fresh obtained NaHTe solution was added to nitrogen-saturated 200 mL 2.5  103 mol L1 CdCl2 aqueous solution completely. Successively, stabilizing agent TGA (1.0 mmol) was added, then adjusted to pH 10 with aqueous NaOH. The mixture was subject to refluxing at 95 °C for 2 h under strong stirring, the color of the precursor’s mixture turned to orange, stable water-soluble TGA-capped CdTe was obtained. Fluorescence detection

Chemicals and apparatus Chlortoluron (P97.0% purity) was purchased from Jiangsu Kuaida Agrochemical Co., Ltd. (Jiangsu, China). Tris–HCl buffer solution (pH = 8.7) was used as buffer solution for all the experiments, by mixing 0.05 mol L1 Tris hydroxy methyl aminomethane and 0.1 mol L1 HCl. All chemicals were of analytical reagent grade and used without further purification, and all solutions were prepared with double deionized water (DDW). Fluorescence spectra was recorded at room temperature with a RF-5301 PC spectra fluorophotometer (Shimadzu, Japan). UV–Vis absorption spectra was performed using a Carry50 UV–Vis spectrophoto-meter (Varian, USA). Transmission Electron Microscopy (TEM) images of CdTe and CDs were obtained on a JEM-2100F Transmission electron microscope with 120 kV acceleration voltage. All pH measurements were made with a pHS-3C pH precision pH meter (Shanghai ray magnetic instrument plant, China).

Cl

HN

A certain mounts of CDs, CdTe, was dropped into a series of 5 mL colorimetric tube. Then, different concentrations of chlortoluron were added respectively. Finally, the mixture was diluted with pH 8.7 Tris–HCl buffer solution to final volume, shaken thoroughly. After 5 min reaction, the fluorescence spectra was measured in room temperature at kex = 315 nm. Both excitation and emission slit width were of 5 nm. Results and discussion Characterization of CDs and CdTe TEM image was used to qualitatively study the morphology of CdTe and CDs. Fig. 2A and B shows that both CDs and CdTe were monodispersed and displayed individual particles. The sizes of CdTe and CDs were around 5 nm and 3 nm respectively. The UV– Vis absorption spectra and fluorescence emission spectra of CDs and CdTe were performed in Fig. 2C. The maximal absorption and emission peaks of the CDs were at 380 nm and 432 nm respectively, and those of CdTe were at 495 nm and 570 nm. The quantum yield (Uu) of CDs and CdTe in our experiments was calculated by using rhodamine 6G (Us = 0.95) as the reference standard [20,21]

Uu ¼ Us  O

N

Fig. 1. The chemical structure of chlortoluron.

F u As  F s Au

where Fu and FS are the areas under the fluorescence curves of the QDs and the standard respectively. Au and AS are the absorbance of the sample and standard at the excitation wavelength, respectively. The Uu value of CDs was found to be 68%, and such of CdTe was 57%. The above results demonstrated that both CDs and CdTe

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

H. Tao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx

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Scheme 1. Schematic illustration for the fluorescence quenching of CdTe–CDs system by chlortoluron.

B

A

0.8

b

C

d

400

0.6

c

IF

300 200

0.4

a

A

500

0.2

100

0.0

0 300 350 400 450 500 550 600 λ

/ nm

Fig. 2. A: TEM image of CdTe; B: TEM image of CDs; C: the absorption and emission spectra of CDs and CdTe (a: absorption of CDs; b: emission spectra of CDs; c: absorption of CdTe; d: emission spectra of CdTe).

were spherical morphology, homogeneous distribution and maintained good performance in terms of photoluminescence.

FRET system construction Good spectral overlapping between donor emission spectral and acceptor absorption spectral is remarkable in getting high energy transfer efficiency. The absorption spectra of CdTe (Fig. 2C curve c) and emission spectra of CDs (Fig. 2C curve b) were at 432 and 510 nm respectively, they give a different of 78 nm, less than 100 nm. According to the reference mention equation [22], overlap integrals (J) were estimated to be 9.48  1014 cm3 L mol1, and suitable J values suggest the energy transfer phenomenon occurred with high probability. To minimize the contribution of direct excitation to donor fluorescent intensity, the FRET measurements were at kex = 315 nm.

The established FRET system could be conformed by changing the concentration of the donor or acceptor. When fixed the amount of CdTe and increased the quantities of CDs (Fig. 3a), CdTe fluorescence intensity was observed to be enhanced owning to more donors transfer energy to acceptors. To further investigate the FRET process, the increase of CdTe was studied by keeping the amount of the CdTe fixed (Fig. 3b). As expected, a significant enhancement of CdTe fluorescence intensity and the corresponding quenching of the CDs emission spectra were observed, due to more acceptors to accept the energy from donors. Results suggest that a FRET process occurs between CDs and CdTe. Efficiency of energy transfer depends on how many donors transfer energy to one acceptor. When fixed the dosage of CdTe 2.0  105 mol L1, with the increasing of CDs concentrations from 0 to 2.8  105 mol L1, the fluorescence intensity of CdTe increased from 443 nm to 604 nm, When CDs concentrations are higher than 2.8  105 mol L1, with the increasing of CDs, CdTe fluorescence intensity

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

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800

600

IF

would not increase any more. That’s to say when the concentration of CDs at 2.8  105 mol L1 this FRET system reached steadystate, thus the best ratio of CDs and CdTe was 7:5. The CDs–CdTe energy transfer strategy is illustrated in Fig. 4, it could be obviously observed that the emission intensity of CdTe was enhanced upon addition of a CDs solution. The FRET efficiency and the distance between the donor and the acceptor were also calculated. Base on previously Ref. [23,24], the FRET efficiency between CDs and CdTe could reach 57%, and the distance of the donor–acceptor pair was calculated to be about 4.6 nm, which was smaller than 7 nm, an appreciable distance for energy transfer phenomenon to occur.

f a

400

200

0 350

400

450

500

550

600

λ / nm

Factors affecting the detection of chlortoluron with CDs–CdTe system

Fig. 3a. Effect of the concentration of CdTe on FRET system. CdTe (a–f: 0.0, 5.0, 10.0, 15.0, 20.0, 25.0)  106 mol L1; CDs: 3.2  105 mol L1.

700 600 500

IF

400 300 200 100

d a

0 350

400

450

500

550

600

λ / nm Fig. 3b. Effect of the concentration of CDs on FRET system. CDs: (a–c: 0, 1.4, 2.8, 3.2)  105 mol L1; CdTe: 2.0  105 mol L1.

In order to establish the optimum analytical system to detect chlortoluron, the effect of critical parameters include pH, buffer medium and time needed for fluorescence quenched have been investigated. In order to investigate how pH influences the CDs–CdTe– chlortoluron system, 2.8  105 mol L1 CDs, 2.0  105 mol L1 CdTe were added to a 5 mL tube, and then 4.0  109 mol L1 chlortoluron was added and brought to the volume by different buffer medium. Experiment showed that in acid medium, the fluorescence of CdTe was in low intensity owing to the protonation of the surface binding thiolates. Thus, the effect of pH on the CDs–CdTe–chlortoluron system was investigated at pH 8.0–9.1, as shown in Fig. 5. It can be found that the pH values at pH 8.0–8.6 the quenching fluorescence intensity of chlortoluron to CdTe changed slightly, while pH values increased to 8.7, the fluorescence intensity changed dramatically. At pH higher than 8.7, chlortoluron quenched the fluorescence of CdTe slightly, the reason might be at high pH the deprotonation of carboxyl groups in the surface of TGA–CdTe, which could deaden the hydrogen-bond between the TGA–CdTe and chlortoluron. Besides, the influence of different buffers on the fluorescence intensity of the system was studied by using Na2B4O7–HBO3, Tris–HCl and barbitone sodium–HCl buffer solution at pH 8.7. The optimal buffer was Tris–HCl buffer. Therefore, the Tris–HCl buffer with pH 8.7 was selected for this work. The effect of time was then investigated. Experiment results showed that, the reaction between CDs–CdTe and chlortoluron reached the equilibrium in room temperature within 5 min, and the fluorescence of CDs–CdTe–chlortoluron system was stable for at least 1.0 h. The fluorescence signals of the system were recorded at the Tris–HCl

700

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600 500

a

70

60

b

50

ΔIF

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400 300

40 200 30

100 0 350

20

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λ / nm Fig. 4. The fluorescence spectra of CDs (a), CdTe (b) and the mixture of CDs and CdTe (c) CdTe: 2.0  105 mol L1; CDs: 2.8  105 mol L1.

8.0

8.2

8.4

8.6

8.8

9.0

9.2

pH Fig. 5. The difference of the CDs–CdTe system with or without chlortoluron at pH 8.0–9.1.

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

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2.8

Quenching mechanism of chlortoluron

2.4

Fig. 6 illustrated the effect of chlortoluron concentration to the FRET system. With the addition of free chlortoluron to mixture solution of CDs and CdTe, fluorescence of CdTe was quenched quickly, while fluorescence of CDs kept almost stable. Thus, the CDs–CdTe–chlortoluron system can be constructed to analysize the concentration of chlortoluron. The interaction studies of chlortoluron with CDs–CdTe system was studied by spectrofluorometry at three temperatures (293, 398 and 303 K). In order to clarify the fluorescence quenching mechanism, the Stern–Volmer equation was utilized to process the data [25,26].

F0 / F

buffer medium with pH 8.7, after the reaction lasted for 5 min in room temperature.

293K

298K

2.0

303K

1.6

1.2

0

1

2

3

4

5

C × 10 mol/L -8

F0 ¼ 1 þ K SV ½C ¼ 1 þ s0 K q ½C F

Fig. 7. Stern–Volmer plots for the fluorescence quenching of CdTe by chlortoluron at pH 8.7 in Tris–HCl buffer at 293, 298, and 303 K.

700 600

a

500 400

0.8

0.6

a A

where F0 and F are the fluorescence intensity of the CdTe in the absence and presence of chlortoluron, respectively. Ksv is the Stern–Volmer quenching rate constant, which is a quenching efficiency measurement, and [C] is the concentration of quencher, s0 is the life time of fluorophore (the s0 for the CdTe is taken as 2.6  108 s) [27], Kq is quenching rate constants, it could be calculated by the equation Kq = Ksv/s0. In order to confirm the quenching mechanism, the procedure of the fluorescence quenching was first assumed to be dynamic quenching [28]. Fig. 7 displays the Stern– Volmer plots of the quenching of CdTe by chlortoluron at different temperatures. Based on the experimental data in Fig. 7, the corresponding Ksv at 293, 298 and 303 K are 3.68  107, 3.04  107, 1.99  107 L/mol respectively. Thus, the calculated Kq values at 293, 298 and 303 K are 1.40  1015, 1.16  1015, 7.60  1014 M1 s1, respectively. In general, maximum collisional quenching constant (Kq) is 2.0  1010 M1 s1. Considering the fact that, in our experiments, Kq of CdTe quenching procedure initiated by chlortoluron are much greater than 2.0  1010 M1 s1, and that Ksv inversely correlated with temperature, it can be concluded that the quenching process is not initiated by dynamic collision quenching, but probably by static quenching resulting from the formation of CdTe–chlortoluron complex. UV–Vis absorption measurement is a simple method applicable to explore the structural changes of compound [29,30]. In order to further verify the quenching mechanism, the UV–Vis absorption

c

0.4

0.2

0.0 300

350

400

450

500

550

λ / nm Fig. 8. UV–Vis absorption spectra of CdTe in the absence and presence of different concentrations of chlortoluron. Chlortoluron: (a–d: 0, 282.1, 564.2)  1010 mol L1; CdTe: 5.0  105 mol L1.

spectra of CdTe in the absence and presence of chlortoluron were recorded. As shown in Fig. 8, addition of chlortoluron to a fix concentration CdTe led to a gradual decrease in CdTe absorption, while keeping the location of the peak unchanged. The above results can be rationalized in terms of interaction between chlortoluron and CdTe QDs in the ground state through complex formation, which accordance with the result of modified Stern–Volmer curve. We thus conjecture that the formation of a complex between TGA capping agent of the QDs and chlortoluron result in fluorescence quenching of TGA-CdTe.

IF

i

300

Detection of chlortoluron

200

The linear range for determination of chlortoluron was estimated under optimum conditions. It was found that quenching effect of chlortoluron on fluorescence of CdTe was concentrationdependent and could be described by Stern–Volmer equation .

100 0 350

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λ / nm Fig. 6. The quenched of chlortoluron to the FRET system chlortoluron: (a–i: 0, 4.7, 14.2, 47, 141.5, 283.0, 471.7, 564.2, 849.1)  1010 mol L1. CDs: 2.8  105 mol L1; CdTe: 2.0  105 mol L1.

F0 ¼ 1 þ K SV ½C F Fig. 9 shows the Stern–Volmer plots. A good linear relationship was observed at the concentration of chlortoluron from 2.4  1010 mol L1 to 8.5  108 mol L1, with a correlation coefficient of

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

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F0 / F

6

3.5

may fulfill the requirement for simple, sensitive, and quantitative detection of chlortoluron.

3.0

Selectivity study To test the ability of the proposed method for analysis real samples, the interference of foreign substance were studied, in the present of 1.0  106 g/L chlortoluron, a tolerable error within ± 5.0%. Results was showed in Table 2. It can be seen that relatively high 2 mounts of K+, Na+, Ca2+, Zn2+, Fe2+, Pb2+, Cu2+, Hg2+, Cl, NO 3 , CO3 , 2 SO4 , dymrone, soproturon, difenoxuron have little interference. All these promote high selectivity of the proposed platform.

2.5 2.0 1.5 1.0

Determination of chlortoluron in irrigation water samples 0

2

4

6

8

10

C × 10 -8mol.L-1 Fig. 9. Stern–Volmer plot of the fluorescence intensity of CdTe versus the chlortoluron concentration. The concentration of chlortoluron were: (a–m: 4.7, 9.4, 18.9, 37.7, 70.8, 94.3, 141.5, 188.7, 283.1, 377.6, 471.7, 849.1)  1010 mol L1.

Table 1 Comparing of the proposed method with previous reports for determination of chlortoluron. Method

Liner range (mol L1)

LOD (mol L1)

Refs.

This work HPLC MIP m-CPE CMIA

2.4  1010–8.5  108 4.7  109–7.1  107 1.0  108–1.0  104 4.0  107–1.0  104 2.0  108–2.0  107

7.8  1011 1.2  109 2.4  109 2.9  107 1.3  108

[3] [6] [7] [9]

The applicability of the developed method in environmental matrices was tested by determination of chlortoluron in irrigation water samples. Sample preparation was carried out with direct determination method according to previous report. 500 lL of this prepared solution was used to perform based on the procedure described in Section 2.4. The chlortoluron contents in irrigation water samples were derived from the standard curve and regression equation mention in Section ‘Detection of chlortoluron’. The recovery was evaluated by using the standard addition method, results were listed in Table 3. It was found that the recovery in this FRET process is sufficient, in the range of 95.8% to 102.5%, with relative standard deviation (RSD) less than 3.48%, validating quite well performance of our newly developed FRET detection method. Hence, the new FRET strategy provided a simple and convenient way to analysis chlortoluron directly in real irrigation water samples. Conclusions

Table 2 Effects of interfering substances on fluorescence. Interferant

Added concentration (g/L)

Change of fluorescence intensity (%)

K+, Na+, Cl, NO 3 Zn2+, Fe2+, Cu2+ 2 2 CO3 , SO4 Ca2+ Pb2+ Hg2+ Dymrone Soproturon Difenoxuron

5.0  105 5.0  105 5.0  105 5.0  105 4.0  105 4.0  105 3.0  105 3.0  105 3.0  105

0.7 1.6 1.7 0.9 2.9 4.1 2.7 3.1 3.5

0.9992. Linear regression equation was F0/F = 0.28c + 1.0. Statistical analysis reveals a detection limit (LOD) of chlortoluron calculated following the 3r IUPAC criteria as low as 7.8  1011 (n = 11). A comparison between the proposed method and other reported methods for quantitative analysis of chlortoluron was summarized in Table 1. It can be seen that the superiority of some reported works in dynamic range, while the LOD obtained in this work has some improvement comparing with some others. Therefore, based on above mentioned results, the FRET-based method

To conclude, we have constructed a newly FRET system based on CDs and CdTe, and the proposed approach was applied in quantitative analysis ultra-trace chlortoluron for the first time. In initial stage, energy transfers from CDs to CdTe which leads to the fluorescence quench of CDs and corresponding enhancement fluorescence of CdTe, the FRET system and energy transfer parameters were studied in details. Upon the addition of chlortoluron, fluorescence quench of CdTe occurs, we optimized some important factors which would affect the quenched efficiency. Under the optimized conditions, linear regression equation shows the linear range from 2.4  1010 mol L1 to 8.5  108 mol L1 and the attenuation of fluorescence intensity can clearly be detected down to 7.8  1011 mol L1 (S/N = 3) in solution was obtained. Moreover, the quenching mechanism of chlortoluron to CdTe was studied, and quenching mechanism was that the formation of a ground state complex between TGA capping agent of QDs and chlortoluron result in fluorescence quenching of TGA–CdTe. The newly construction platform was applied to the determination of chlortoluron in irrigation water samples by using the standard addition method, the recovery were found to be 95.8% to 102.5% with RSD less than 3.48%. By means of the strategy of CDs–CdTe FRET system, it is promising to develop a general optical method for rapid, selective analyses in other pesticides.

Table 3 Analytical results of serum samples. Samples

Found (1010 mol L1, n = 6)

RSD (%, n = 6)

Added (1010 mol L1)

Total found (1010 mol L1)

Recovery (%)

1 2 3

22.6 23.6 19.8

2.67 1.89 3.48

23.6 23.6 23.6

46.5 47.8 42.4

101.3 102.5 95.8

Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

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Please cite this article in press as: H. Tao et al., A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultratrace chlortoluron in water, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.10.020

A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultra-trace chlortoluron in water.

In this paper, a fluorescence resonance energy transfer (FRET) system between fluorescence carbon dots (CDs, donor) and CdTe quantum dots (CdTe, accep...
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