Room-Temperature Phosphorescent Discrimination of Catechol from

Dec 27, 2012 - RTP response of STPP-Mn-ZnS QDs to the three isomers was pH- ... isomers was observed at pH 8.0: catechol enhanced the RTP intensity...
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Room-Temperature Phosphorescent Discrimination of Catechol from Resorcinol and Hydroquinone Based on Sodium Tripolyphosphate Capped Mn-Doped ZnS Quantum Dots He-Fang Wang, Ye-Yu Wu, and Xiu-Ping Yan* State Key Laboratory of Medicinal Chemical Biology and Research Center for Analytical Sciences, College of Chemistry, Nankai University, 94 Weijin Road, Tianjin 300071, China S Supporting Information *

ABSTRACT: A room-temperature phosphorescence (RTP) strategy was developed for direct, additive-free discrimination of catechol from resorcinol and hydroquinone based on sodium tripolyphosphate capped Mn-doped ZnS quantum dots (STPP-Mn-ZnS QDs). The RTP response of STPP-Mn-ZnS QDs to the three isomers was pHdependent, and the greatest difference in the RTP response to the isomers was observed at pH 8.0: catechol enhanced the RTP intensity of the QDs, while resorcinol and hydroquinone had little effect on the RTP intensity of the QDs. The enhanced RTP intensity of 1 μM catechol was not affected by the coexistence of 30 μM resorcinol and 50 μM hydroquinone at pH 8.0. The detection limit of this RTP method was 53 nM catechol, and the precision was 3.2% (relative standard deviation) for five replicate detections of 1 μM catechol. The discrimination mechanism was ascribed to the weak bonded ligand of STPP-Mn-ZnS QDs and the different interaction between the three isomers and STPP-Mn-ZnS QDs. The strong binding of catechol to Zn resulted in the extraction of Zn from the surface of STPP-Mn-ZnS QDs and the generation of holes that were trapped by Mn2+ to form Mn3+. Catechol also promoted the reduction of Mn3+ into Mn2+ excited state, thus ultimately inducing the enhanced RTP response of STPP-Mn-ZnS QDs.

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spectrophotometric method has the advantages of convenience and low-cost, but requires complicated chemometrics treatments of UV−vis spectra, or several additives for indirect dye fluorometry.18 The room temperature phosphorescence (RTP) of QDs is a less usual phenomenon than the fluorescence of QDs,19 but provides several distinguished advantages over fluorescence, such as the wider gap between the excitation and emission spectra, the longer emission lifetime, and the lowest interference of the short-lived autofluorescence and scattering light.19 Recently, the RTP of QDs has attracted growing interest in optosensing with the merits of effectively avoiding tedious sample pretreatment due to the much longer lifetime of the RTP over the scattering light and autofluorescence of complex matrix.20−30 However, to the best of our knowledge, the application of such RTP in the discrimination of organic isomers has not been reported yet. Herein, we report an RTP strategy for direct, additive-free discrimination of catechol from resorcinol and hydroquinone based on sodium tripolyphosphate capped Mn-doped ZnS quantum dots (STPP-Mn-ZnS QDs). The RTP response of STPP-Mn-ZnS QDs to the three isomers was pH-dependent.

he discrimination of the isomers of organic compounds is a great challenge in organic and analytical chemistry due to their similar properties.1,2 Catechol, resorcinol, and hydroquinone are well-known organic isomers that are frequently used as industrial reagents in the production of plastic, tanning, paint, cosmetics, dyes, rubber, and pharmaceuticals,3,4 and are also the important side products in oil refineries, coal tar, steel, saw, and pulp mills.3 Catechol, resorcinol, and hydroquinone are among the list of the second kind of environmental pollutants due to their toxicity.4,5 Catechol also shows the biological importance such as antivirus, antioxidation, and regulator of the activities of some enzymes,6,7 widely existing in plants such as fruits, teas, vegetables, tobaccos, and traditional Chinese medicines.6 Consequently, the discrimination of catechol from resorcinol and hydroquinone is of great significance for guaranteeing environmental and food safety, as well as human health. To date, the reported strategies for the determination of catechol, resorcinol, and hydroquinone have spanned electrochemical,8−11 chromatographic,12,13 and spectrophotometric methods.14−16 For the merits of low maintenance costs, high accuracy, and excellent sensitivity, an electrochemical method has been widely explored, though the electrode modification is always required due to the broad overlapped peaks of catechol and hydroquinone on the bare glassy carbon electrode (GCE).17 The chromatographic method has minimal cross-interference, but needs sample pretreatment and long testing period.4 In contrast, a © 2012 American Chemical Society

Received: November 21, 2012 Accepted: December 27, 2012 Published: December 27, 2012 1920

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QDs in the absence and presence of 2 mM catechol, resorcinol, and hydroquinone was dialyzed using a dialysis bag with molecular weight cutoff 12 000−14 000 (Shanghai Dingguo Biology, Shanghai, China) in 80 mL of 10 mM Tris-HCl buffer (pH 8.0), and the dialysate after acidification with 1% HNO3 was analyzed on an X series ICP-MS instrument (Thermo Elemental, Cheshire, U.K.). For the determination of the Mn, Zn, and P in the solid QDs, 1.6 mg of STPP-ZnS-Mn (or MPA-Mn-ZnS) QDs was dispersed in 80 mL of 10 mM Tris-HCl buffer (pH 8.0) and acidified with 1% HNO 3 before ICP-MS determination. The contents of carbon (C) before and after dialysis were determined on an Elementar Vario EL elementary analyzer (Elementar, Germany). The RTP measurements were performed on an F-4500 spectrofluorometer equipped with a plotter unit and a quartz cell (1 cm × 1 cm) (Hitachi, Japan). The excitation wavelength was 316 nm when the spectrofluorometer was set in the phosphorescence mode. The slit widths of excitation and emission were 10 and 20 nm, respectively. The PMT voltage was set at −950 V. A 400 mg L−1 STPP-Mn-ZnS or MPA-Mn-ZnS suspension was prepared and stored under ambient condition. A 10-mL mixture of 2 mg L−1 QDs, 10 mM Tris-HCl buffer, and a given concentration of analyte standard solution were mixed thoroughly before RTP measurement.

The greatest difference in the RTP response of QDs to the isomers was observed at pH 8.0. Catechol enhanced the RTP intensity of the QDs, while resorcinol and hydroquinone had little effect on the RTP intensity of the QDs. Moreover, the enhanced RTP intensity of 1 μM catechol was not affected by the coexistence of 30 μM resorcinol and 50 μM hydroquinone at pH 8.0. The discrimination mechanism was also discussed.

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EXPERIMENTAL SECTION Chemicals. All chemicals used were at least analytical grade and used without further purification. Zn(CH3COO)2·2H2O, Mn(CH3COO)2·4H2O, and Na2S·9H2O were from Tianjin Kaitong Chemicals Co. (Tianjin, China), the Second Chemicals Co. of Shenyang (Shenyang, China), and Tianjin Sitong Chemicals Co. (Tianjin, China), respectively. Ultrapure water (18.2 MΩ cm) was obtained from a WaterPro water purification system (Labconco Corporation, Kansas City, MO). Catechol (CC), resorcinol (RC), hydroquinone (HQ), tris(hydroxymethyl) aminomethane (Tris), and sodium borate were obtained from Tianjin Guangfu Fine Chemical Research Institute (Tianjin, China). STPP and mercaptopropionic acid (MPA) from Aladdin (Shanghai, China) were used as ligands to synthesize Mn-doped ZnS QDs. The Tris-HCl (0.1 mol L−1, pH 6.5−10.0), NaB4O7− NaOH (0.025 mol L−1, pH 10.0), and NaHCO3−NaOH (0.025 mol L−1, pH 11.0) were used as the buffer solutions. Synthesis of STPP-Mn-ZnS QDs. The STPP-Mn-ZnS QDs were synthesized according to Wang et al.29 Briefly, in a 100-mL flask, 125 mmol Zn(CH3COO)2, 250 mmol of STPP, and 5 mmol Mn(CH3COO)2 were dissolved in 30 mL of ultrapure water. The mixture was stirred at room temperature for 30 min, and then 10 mL of Na2S (12.5 M) aqueous solution was added dropwise in an ice bath and with continued stirring for 10 min. The mixture was further stirred at room temperature for 2 h. Finally, the resultant STPP-Mn-ZnS QDs were centrifuged and washed with ultrapure water and absolute ethanol three times, and dried in vacuum. The STPP-Mn-ZnS QDs contained 20.3% Zn, 0.061% Mn, and 2.7% P.29 The MPA capped Mn-doped ZnS (MPA-Mn-ZnS) QDs was prepared as follows:31 50 mL of 0.04 M MPA, 5 mL of 0.1 M Zn(CH3COO)2, and 2 mL of 0.01 M Mn(CH3COO)2 were added to a 100 mL three-necked flask. The mixed solution was adjusted to pH 11 with 1 M NaOH and stirred under argon at room temperature for 30 min. A 5 mL portion of 0.1 M Na2S was then quickly injected into the solution. After the mixture was kept stirring for 20 min, the solution was aged at 50 °C under air for 2 h. Finally, the resultant QDs were precipitated with ethanol, separated by centrifuging, washed with ethanol, and dried in vacuum. The MPA-Mn-ZnS QDs contained 17.2% Zn, 1.6% Mn, and 6.2% C. Methods. The cyclic voltammograms were monitored with a model LK98BII microcomputer-based electrochemical analyzer (Tianjin Lanlike High-Tech Company, Tianjin, China). A three-electrode system was employed with Pt wire as the counter electrode, Ag/AgCl/KCl as the reference electrode, and a 3 mm-diameter glassy carbon electrode (GCE) as the working electrode. The GCE was polished and ultrasonically cleaned with ethanol and ultrapure water before use. The STPP-Mn-ZnS QDs modified GCE was prepared by dropping 5 μL of 0.4 g L−1 QDs to the surface of the cleaned GCE, and then drying in dark at room temperature. UV spectra were recorded on a UV-3600 UV− vis−NIR spectrophotometer (Shimadzu, Japan). For the determination of Mn, Zn, and ligand in the solution of the QDs, 5 mL of 320 mg L−1 STPP-ZnS-Mn (or MPA-Mn-ZnS)

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RESULTS Effect of the Capping Agent of Mn-ZnS QDs on the Discrimination of the Isomers. The capping agent is usually used to keep the colloidal nanocrystal stable in solution, but it also influences the chemical accessibility of the nanocrystals to the target analytes. To elucidate the effect of the capping agent on the interaction between the isomers and Mn-ZnS QDs, we compared the RTP response of MPA-Mn-ZnS QDs and STPP-Mn-ZnS QDs to catechol, resorcinol, and hydroquinone (Figure 1). STPP-Mn-ZnS QDs exhibited higher sensitivity and

Figure 1. RTP response of STPP-Mn-ZnS and MPA-Mn-ZnS QDs (2 mg L−1) to catechol (CC), resorcinol (RC), and hydroquinone (HQ) (all in 10 μM) at pH 8.0 (buffered by 10 mM Tris-HCl).

better discrimination ability to the three isomers than MPA-MnZnS QDs. To get higher sensitivity and better discrimination of the three isomers, STPP-Mn-ZnS QDs was chosen for further studies. RTP Response of STPP-Mn-ZnS QDs to Catechol, Resorcinol, and Hydroquinone. Although the chemical structure of catechol, resorcinol, and hydroquinone is very similar, the RTP responses (both the excitation and emission) of the STPP-Mn-ZnS QDs to the three isomers were quite different (Figure 2). In the presence of catechol, the RTP 1921

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Figure 2. RTP excitation and emission spectra of STPP-Mn-ZnS QDs (2 mg L−1) in the absence and presence of catechol (CC), resorcinol (RC), and hydroquinone (HQ, all in 10 μM) at pH 8.0 (buffered by 10 mM Tris-HCl) and pH 10.0 (buffered by 2.5 mM NaB4O7−NaOH).

Turn-On RTP Detection of Catechol by STPP-Mn-ZnS QDs. To further demonstrate the enhanced RTP response of STPP-Mn-ZnS QDs to catechol, the RTP emission spectra of 2 mg L−1 STPP-ZnS-Mn QDs upon the addition of catechol at different concentration buffered by 10 mM Tris-HCl (pH 8.0) are shown in Figure 4. In the examined catechol concentration

emission and excitation of QDs were greatly enhanced at pH 8.0, but obviously quenched at pH 10.0. Resorcinol displayed little effect on the RTP excitation and emission of QDs at both pH 8.0 and pH 10.0. Hydroquinone, however, only showed quenching effect at pH 10.0. The pH-related RTP responses of the STPP-Mn-ZnS QDs to the three isomers are further revealed in Figure 3. In the pH

Figure 4. Turn-on RTP response of 2 mg L−1 STPP-Mn-ZnS QDs upon addition of catechol (CC) at pH 8.0 buffered by 10 mM TrisHCl. Inset shows the enhanced RTP intensity (monitored at 595 nm) of 2 mg L−1 STPP-Mn-ZnS QDs against the concentration of catechol.

Figure 3. pH-dependent RTP response of STPP-Mn-ZnS QDs (2 mg L−1) to catechol, resorcinol, and hydroquinone (all in 10 μM). The buffer is 10 mM Tris-HCl for pH 6.5−9.5 and 2.5 mM NaB4O7−NaOH for pH 10.0 and 2.5 mM NaHCO3−NaOH for pH 11.0.

range from 0.5 μM to 20 μM, the enhanced RTP emission of STPP-Mn-ZnS was observed. To evaluate the sensitivity of the turn-on RTP detection of catechol at pH 8.0, the RTP emission intensity of STPP-Mn-ZnS QDs at 595 nm was monitored as a function of the concentration of catechol (inset in Figure 4). A linear relationship of the ΔP against the concentration of catechol was observed in the range 0.5−5 μM with a correlation coefficient of 0.9962 and the calibration function ΔP = 13.6 + 97.6 CCC (where CCC is the concentration of catechol in μM). The limit of detection (LOD), calculated as the concentration of catechol which produced an enhanced RTP 3 times the

range from 6.5 to 11.0, resorcinol showed little influence on the RTP emission of STPP-Mn-ZnS QDs, but RTP response of STPP-Mn-ZnS QDs to catechol and hydroquinone was pH-dependent. The RTP intensity of STPP-Mn-ZnS QDs was enhanced by the addition of catechol in pH 6.5−9.0, with the maximal enhanced RTP intensity (ΔP = P − P0) at pH 8.0; however, the quenched RTP response of catechol was observed in pH 9.5−11.0. As to hydroquinone, the RTP response at pH 6.5−8.5 was less sensitive, and the quenched RTP response was also observed in pH 9.0−11.0. 1922

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change below 5%, Table S1). Other ions such as K+, Na+, and Ca2+ were permitted at 1000-fold, and Mg2+ was tolerable at 700-fold. Amino acids, such as histidine, tryptophan, and valine, at 200-, 250-, and 500-fold did not affect the detection of 1 μM catechol. However, the coexistence of 7-fold ascorbic acid would bring signal change of 9.7%.

standard deviation of the blank signal, was 53 nM. The precision for five replicate detections of 1 μM catechol was 3.2% (RSD). Interference with Quantitative Analysis of Catechol. As shown above, the RTP response of catechol, resorcinol and hydroquinone was pH-dependent. The lowest interference from resorcinol and hydroquinone was at pH 8.0. Consequently, pH 8.0 was selected to investigate the interference of catechol determination. The enhanced RTP intensity of STPPMn-ZnS QDs upon the addition of 1 μM catechol was unaffected by 30 μM resorcinol and 50 μM hydroquinone (signal

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DISCUSSION The discrimination of catechol from resorcinol and hydroquinone by RTP of STPP-Mn-ZnS QDs was related to the properties of the QDs and the three isomers (Scheme 1). The surface state of the QDs, i.e., the binding of the stabilizer STPP onto the surface of the QDs, had great influence on the accessibility of the QDs to the analytes. The tighter binding of the stabilizer leads to the lessened accessibility of the QDs to the analytes. Compared with MPA-Mn-ZnS QDs, the STPP-Mn-ZnS QDs were more accessible to the analytes due to the weaker binding of STPP. The concentration of STPP in the dialysate of STPP-MnZnS QDs was about 80% of the total STPP attached onto the surface of STPP-Mn-ZnS QDs,29 while the concentration of MPA in the dialysate of MPA-Mn-ZnS QDs was about 58% of the total MPA attached onto the surface of MPA-Mn-ZnS QDs (Table S2 in the Supporting Information). Consequently,

Scheme 1. Illustration for the Mechanism of Enhanced RTP Response of STPP-Mn-ZnS to Catechol

Figure 5. UV spectra of catechol (CC), resorcinol (RC), and hydroquinone (HQ) in the absence and presence of Zn2+ or Mn2+ at pH 8.0 (buffered by 10 mM Tris-HCl) and pH 10.0 (buffered by 2.5 mM NaB4O7−NaOH). 1923

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STPP-Mn-ZnS QDs exhibited the higher sensitivity and better discrimination of the three isomers than MPA-Mn-ZnS QDs. The RTP emissions of Mn-doped ZnS QDs originated from the triple transition of Mn2+ (4T1−6A1) incorporated into the ZnS host lattice.20 The excitation of Mn2+ takes place via energy transfer from the ZnS host, starting with the creation of the electron−hole pair (Scheme 1).32,33 The Mn2+ then traps a hole and turns into Mn3+ (process 1). Subsequent recombination of Mn3+ with an electron results in Mn2+ in the excited state (process 2) to emit the well-known orange emission of Mn2+ (process 3).32 Any factors affecting the processes 1−3 would change the RTP emission of Mn-doped ZnS QDs. Catechol, resorcinol, and hydroquinone, with two phenolic hydroxyl groups, have reasonable reducibility that would affect process 2. Usually, resorcinol shows the lowest reducibility, as revealed by the highest oxidation peak potentials in most of the reported cyclic voltammograms.4 Catechol and hydroquinone, however, exhibit similar reducibility as their oxidation peaks are always overlapped.4 Besides, the dihydroxyl groups of these three isomers also show reasonable binding to the metals that would have influence on process 1. For example, the adjacent two phenolic hydroxyls of catechol display high binding tendency toward metals, as the resultant complexes have the stable structure of five-membered rings.34,35 Thus, the reducibility and binding tendency toward metals of these isomers would have diverse effects on processes 1−3 of Mn-ZnS QD excitation and emission (Scheme 1). Binding of Catechol, Resorcinol, and Hydroquinone to the Metals. The binding tendency of catechol, resorcinol, and hydroquinone toward Zn2+ and Mn2+ was demonstrated by the UV spectra in Figure 5. The UV spectrum of catechol shows obvious changes upon addition of Zn2+ (red-shift at both pH 8.0 and pH 10.0) and Mn2+ (enhanced absorbance at pH 8.0 and new absorbance peak at pH 10.0), and that of hydroquinone only shows variations in the presence of Mn2+ (new absorbance peak at pH 8.0 and enhanced absorbance at pH 10.0); however, the UV spectrum of resorcinol is independent of the presence of Mn2+ and Zn2+. This evidence suggests the great difference between the three isomers and the metals. As Zn is massive at the surface of Mn-ZnS QDs, the interaction of catechol and Mn-ZnS QDs would be dominant. The different binding tendency of catechol, resorcinol, and hydroquinone with QDs was also demonstrated by the dialysis experiments (Table S2 and S3 in the Supporting Information). The content of Mn and Zn in the dialysate of STPP-Mn-ZnS QDs increased in the presence of catechol, while it remained constant in the presence of resorcinol. In contrast, the presence of hydroquinone did not change the content of Zn, and only resulted in an increase of the content of Mn in the dialysate of STPP-Mn-ZnS QDs. These results are in accordance with the UV spectra (Figure 5) and suggest that catechol could extract Zn from the surface of the QDs and thus generate more holes, which was helpful to the formation of Mn3+ as the holes could be trapped by Mn2+ (process 1 in Scheme 1).32 Cyclic Voltammetry of Catechol, Resorcinol, and Hydroquinone on STPP-Mn-ZnS QD Modified GCE. The different redox properties of catechol, resorcinol, and hydroquinone at bare GCE and STPP-Mn-ZnS QD modified GCEs are illustrated by the cyclic votammetry measurements (Figure 6). Compared with bare GCE, STPP-Mn-ZnS QDs modified GCE exhibited a peak at around −1.5 V at pH 8.0, which was corresponding to Mn3+/Mn2+ related to the excitation of Mn2+ emission.36 The cyclic voltammograms of catechol, resorcinol, and hydroquinone at STPP-Mn-ZnS QDs modified GCE were

Figure 6. Cyclic voltammograms of bare GCE and STPP-Mn-ZnS QDs modified GCE in the absence and presence of 2 mM catechol (CC), resorcinol (RC), and hydroquinone (HQ) at pH 8.0 (buffered by 10 mM Tris-HCl). The potential scanned in the positive direction from −2.5 to +1.6 V with a scan rate of 100 mV s−1.

also quite different. The peak at −1.5 V of Mn3+/Mn2+ disappeared in the presence of catechol at pH 8.0, indicating the reduction of Mn3+ to (Mn2+)* by catechol. At the same time, the electrochemical reversibility of catechol at STPP-Mn-ZnS QDs modified GCE was worse than that of bare GCE, as revealed by the decreased peak current and the increased peak potential difference between the anodic peak potential and the cathodic peak potential (ΔEp). This evidence suggested that, in addition to the electrode reaction, there existed another electron transport process to catechol, that is, the electron donation to Mn3+ resulting in (Mn2+)* excitation state (process 2 in Scheme 1). The cyclic voltammograms of resorcinol at the bare GCE and STPP-Mn-ZnS QDs modified GCE were almost the same, excluding the interaction of resorcinol and Mn3+. The disappearance of the peak at −1.5 V might be caused by overpotential. However, for hydroquinone, the electrochemical reversibility at STPP-Mn-ZnS QDs modified GCE is improved, as the peak 1924

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current was increased and the ΔEp was decreased. Meanwhile, the peak at −1.5 V can still be observed in the presence of hydroquinone. Thus, hydroquinone could not reduce Mn3+ to (Mn2+)* excitation state, which most probably resulted from the weaker interaction of hydroquinone and Zn in QDs (as revealed by Figure 5 and Table S3 in Supporting Information). Consequently, among the three isomers, only catechol could promote the reduction of Mn3+ to generate the Mn2+ excited state (process 2 in Scheme 1), and in turn result in the enhanced orange emission of Mn2+ 4T1−6A1 (process 3 in Scheme 1) at pH 8.0. At basic pH condition such as pH 10.0, catechol and hydroquinone are most likely to turn into the o-quinone and p-quinone (Figure S1 in the Supporting Information, almost the same UV spectra of hydroquinone and p-quinone at pH 10.0), which are the well-known electron acceptors to quench the QDs photoluminescence intensity.14 Therefore, the quenched RTP response of the QDs to catechol and hydroquinone was observed at pH higher than 9.5.

(10) Du, H. J.; Ye, J. S.; Zhang, J. Q.; Huang, X. D.; Yu, C. Z. J. Electroanal. Chem. 2011, 650, 209. (11) Guo, Q. H.; Huang, J. S.; Chen, P. Q.; Liu, Y.; Hou, H. Q.; You, T. Y. Sens. Actuators, B 2012, 163, 179. (12) Dong, S. Q.; Chi, L. Z.; Yang, Z. Y.; He, P. A.; Wang, Q. J.; Fang, Y. Z. J. Sep. Sci. 2009, 32, 3232. (13) Dong, S.; Chi, L.; Zhang, S.; He, P.; Wang, Q.; Fang, Y. Anal. Bioanal. Chem. 2008, 391, 653. (14) Yuan, J.; Guo, W.; Wang, E. Anal. Chem. 2008, 80, 1141. (15) Nagaraja, P. J. Pharm. Biomed. Anal. 2001, 25, 417. (16) Nagaraja, P. Talanta 2001, 55, 1039. (17) Liu, W.-Z.; Wang, X.-G.; Wu, Q.-S.; Ding, Y.-P. J. Anal. Chem. 2009, 64, 54. (18) Tang, L.; Zeng, G.; Liu, J.; Xu, X.; Zhang, Y.; Shen, G.; Li, Y.; Liu, C. Anal. Bioanal. Chem. 2008, 391, 679. (19) Sánchez-Barragán, I.; Costa-Fernández, J. M.; Valledor, M.; Campo, J. C.; Sanz-Medel, A. TrAC, Trends Anal. Chem 2006, 25, 958. (20) He, Y.; Wang, H.-F.; Yan, X.-P. Anal. Chem. 2008, 80, 3832. (21) Ren, H.-B.; Wu, B.-Y.; Chen, J.-T.; Yan, X.-P. Anal. Chem. 2011, 83, 8239. (22) Tu, R. Y.; Liu, B. H.; Wang, Z. Y.; Gao, D. M.; Wang, F.; Fang, Q. L.; Zhang, Z. P. Anal. Chem. 2008, 80, 3458. (23) Wang, H.-F.; He, Y.; Ji, T.-R.; Yan, X.-P. Anal. Chem. 2009, 81, 1615. (24) Wu, P.; He, Y.; Wang, H.-F.; Yan, X.-P. Anal. Chem. 2010, 82, 1427. (25) Yan, H.; Wang, H. F. Anal. Chem. 2011, 83, 8589. (26) Zou, W. S.; Sheng, D.; Ge, X.; Qiao, J. Q.; Lian, H. Z. Anal. Chem. 2011, 83, 30. (27) Wu, P.; Miao, L.-N.; Wang, H.-F.; Shao, X.-G.; Yan, X.-P. Angew. Chem., Int. Ed. 2011, 50, 8118. (28) He, Y.; Wang, H.-F.; Yan, X.-P. Chem.Eur. J. 2009, 15, 5436. (29) Wang, H.-F.; Li, Y.; Wu, Y.-Y.; He, Y.; Yan, X.-P. Chem.Eur. J. 2010, 16, 12988. (30) Zhang, B. H.; Wu, F. Y.; Wu, Y. M.; Zhan, X. S. J. Fluoresc. 2010, 20, 243. (31) Zhuang, J. Q.; Zhang, X. D.; Wang, G.; Li, D. M.; Yang, W. S.; Li, T. J. J. Mater. Chem. 2003, 13, 1853. (32) Suyver, J. F.; Wuister, S. F.; Kelly, J. J.; Meijerink, A. Nano Lett. 2001, 1, 429. (33) Yang, H.; Santra, S.; Holloway, P. H. J. Nanosci. Nanotechnol. 2005, 5, 1364. (34) Lee, Y. H.; Lee, H.; Kim, Y. B.; Kim, J. Y.; Hyeon, T.; Park, H.; Messersmith, P. B.; Park, T. G. Adv. Mater. 2008, 20, 4154. (35) Kemikli, N.; Kavas, H.; Kazan, S.; Baykal, A.; Ozturk, R. J. Alloys Compd. 2010, 502, 439. (36) Wang, X. F.; Xu, J. J.; Chen, H. Y. J. Phys. Chem. C 2008, 112, 17581.

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CONCLUSIONS We have reported the discrimination of catechol from resorcinol and hydroquinione by the RTP method based on STPP-Mn-ZnS QDs. The discriminating ability was ascribed to the easy accessibility of the surface metals of QDs to the isomers of catechol, resorcinol, and hydroquinione, and the different interactions of the three isomers toward STPP-Mn-ZnS QDs. The data presented here could be helpful for the deep understanding of the photoluminescent mechanism of Mn-doped ZnS QDs.

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ASSOCIATED CONTENT

S Supporting Information *

Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: (86)22-23506075. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (No. 2011CB707703), the National Natural Science Foundation of China (No. 20935001, 20977049, 21175073), and the Fundamental Research Funds for the Central Universities.

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REFERENCES

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