Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Preparation of ZnS:Ni/ZnS quantum dots with core/shell structure and application for detecting cefoperazone–sulbactam Jianying Qu a,⇑, Zhuanying Zhu a, Changda Wu a, Lianjie Zhang a, Jianhang Qu b a b
Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, PR China College of Bioengineering, Henan University of Technology, Zhengzhou, Henan 450000, PR 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
ZnS:Ni/ZnS QDs were synthesized
easily with nontoxic. It shows fluorescent characteristic
with good water-solubility and stability. ZnS:Ni/ZnS QDs was firstly used as fluorescent probe to detect CPZ–SBT. This novel method is sensitive with good selectivity and a low detection limit.
a r t i c l e
i n f o
Article history: Received 27 August 2013 Received in revised form 25 October 2013 Accepted 31 October 2013 Available online 7 November 2013 Keywords: Cefoperazone Sulbactam Quantum dots
a b s t r a c t ZnS:Ni quantum dots (QDs) have been synthesized via a water-soluble route, which were coated by ZnS shell through surface modification to give ZnS:Ni/ZnS QDs. The QDs were characterized by atomic force microscope, X-ray diffraction, infrared spectrometry and fluorescent spectrometry. Then, a novel method for the determination of cefoperazone–sulbactam (CPZ–SBT) in aqueous solutions has been developed based on the enhancement of fluorescence of ZnS:Ni/ZnS QDs in the presence of CPZ–SBT. Under the optimal conditions, the enhanced fluorescence intensity (DF) was proportional to CPZ–SBT concentration in the range of 8.0 106–1.0 104 g/L with a detection limit of 1.0 107 g/L. The method was employed for the determination of CPZ–SBT in sample to give satisfactory result. Compared with others, this method was more sensitive, fast and simple with low limit detection. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Cefoperazone–sulbactam (CPZ–SBT) is a combination of antibiotics and enzyme inhibitor. Cefoperazone has B-lactam structure and sulbactam has semi-synthetic B-lactamase inhibitors, when used in combination, it can enhance antibacterial effect and antibacterial spectrum. And it has strong inhibitory effect against staphylococcus, b-lactamase, which were used for the treatment of various diseases [1,2]. At present, a few methods to determine CPZ–SBT have been reported mainly by high performance liquid ⇑ Corresponding author. Tel./fax: +86 0378 3881589. E-mail addresses: [email protected], [email protected] (J. Qu). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.096
chromatography (HPLC) [3–5] and ultra performance liquid chromatography (UPLC) [6]. Quantum dots (QDs) have attracted great interest due to their unique properties and potential applications in the past few decades. Recently, the applications of QDs in fluorescent probes [7], analysis and the detection [8], optical device [9] and fingerprint collection [10,11] are studied. Research showed that core/shell structure and alloy structure QDs could both significantly change the optical and electrical properties [12], which have attracted more and more attention. Here, ZnS:Ni/ZnS QDs with core/shell structure were prepared successfully. And based on the enhancement of fluorescence of ZnS:Ni/ZnS QDs in the presence of CPZ–SBT, a novel method to
J. Qu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
detect CPZ–SBT was established. Compared with other reports [3,4,6], this method was more simple, sensitive and rapid with low limit detection with potential prospect for practical applications.
351
were washed respectively by water and ethanol, and centrifuged. This operation was repeated for several times to remove impurities. Then the products were dried in a hot air oven at 65 °C for 5 h to obtain functionalized ZnS:Ni/ZnS QDs with approximate same size.
Experimental Results and discussions Apparatus Characterization of the ZnS:Ni/ZnS QDs SPA400 scanning probe microscope (Japan’s seiko), F-7000 spectrofluorometer (Japan’s Hitachi), VATAR360 type Fourier transformed infrared spectrometer (the United States, high-power company), UV-5400 UV spectrophotometer (American thermoelectric company), X-PertPro type X-ray diffraction (Dutch Philips), Phs-3 CT pH meter (Shanghai, Dapu instrument Co.), DF-101 Z water bath pot and DZF-250 vacuum drying oven (Zhengzhou, the Great Wall traded Co.) were used for experiments. Materials and reagents HSCH2COOH, NaOH (Tianjin Kemiou chemical reagent Co.), Zn(Ac)22H2O, Ni(Ac)24H2O, Na2S9H2O (Tianjin chemical reagent Co.), CPZ–SBT (Shandong runze pharmaceutical Co.), KH2PO4K2HPO4, KH2PO4-sodium citric, citric acid-sodium citric, and all other materials were analytical reagent grade. Doubly distilled water was used throughout. Synthesis of ZnS:Ni/ZnS QDs By modifying the synthesis methods reported [13], core/shell structure ZnS:Ni/ZnS QDs were obtained according to the following steps: 20 mL 0.1 mol/L of Zn(CH3COO)2, 2 mL 0.005 mol/L of Ni(CH3COO)2, 0.28 mL HSCH2COOH and 68 mL doubly distilled water were added into the three neck flask in turn and pH was adjusted to 11 with NaOH solution. The mixture was purged with N2 for 30 min. After being heated to 80 °C, 10 mL 0.1 mol/L of Na2S solution was added into the solution quickly with stirred magnetically and the mixture was stirred at 80 °C for 2 h. Then, 100 lL 1 mol/L of Zn(CH3COO)2, 12 lL HSCH2COOH, 25 lL 8 mol/L of NaOH and 25 lL 2 mol/L of Na2S were added respectively with stirred for 2 min. The above steps were repeated for 5 times. After 5 min, the proper amount of ethanol was added until a homogeneous solution was obtained. The obtained dispersions
Dynamic force microscope (DFM) characteristic Fig. 1a and b was DFM images of ZnS:Ni/ZnS QDs without and with CPZ–SBT. It was obviously that the synthetic ZnS:Ni/ZnS QDs were uniform with the average size of 60 nm. After interacting with CPZ–SBT, the diameter of ZnS:Ni/ZnS QDs became larger with the average size of about 70 nm. X-ray diffraction (XRD) characterization The XRD figures of ZnS, ZnS:Ni and ZnS:Ni/ZnS were obtained and shown in Fig. 2. It was clear that the three diffraction peaks for the three samples were appeared at the same positions, which were corresponding with the three peaks of ZnS (3 1 1), (2 2 0) and (1 1 1), respectively. Through comparison, Doping with Ni and further coating with ZnS shell did not change peak positions, intensity and number of ZnS, which demonstrated that ZnS:Ni/ZnS has the same crystal structure with ZnS [13]. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) characteristic ICP-AES was employed to test whether Ni existed in ZnS:Ni/ZnS QDs. The experimental results showed that Ni was doped into ZnS:Ni/ZnS successfully and the concentration of Ni in synthetic QDs was 0.301 mg/L. Therefore, the doping percentage of Ni in ZnS:Ni/ZnS was calculated of 1.0%. Infrared radiation (IR) characterization The IR spectra of CHCOOHSH (TGA) and ZnS:Ni/ZnS were shown in Fig. 3. Through comparing Fig. 3a and b, the peak of SAH of TGA at 2568 cm1 disappear for ZnS:Mn QDs, while peaks for C@O at 1581 cm1 and 1386 cm1 appeared. This demonstrated that TGA have combined with the surface of ZnS:Ni/ZnS QDs successfully through sulfydryl. Peak of C@O of ZnS:Ni/ZnS had a little hypochromatic shift due to substituent of C@O made change.
Fig. 1. DFM images of ZnS:Ni/ZnS QDs (a) and ZnS:Ni/ZnS QDs + CPZ–SBT (b).
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Fig. 2. XRD figures of ZnS (a), ZnS:Ni (b) and ZnS:Ni/ZnS (c).
Fig. 4. Fluorescence spectra of ZnS:Ni (a), ZnS:Ni + CPZ–SBT (b), ZnS:Ni/ZnS (c) and ZnS:Ni/ZnS + CPZ–SBT (d).
Fig. 3. IR spectra of TGA (a) and ZnS:Ni/ZnS QDs (b).
Fluorescence spectroscopy Fig. 4 was fluorescence spectra of ZnS:Ni, ZnS:Ni/ZnS in the absence and presence of CPZ–SBT, respectively. Fluorescence difference can be calculated by the formula:
DF ¼ F 0 F
Fig. 5. Fluorescence spectra of ZnS:Ni/ZnS and ZnS:Ni/ZnS interact with different concentrations of CPZ–SBT (a–d): 9.0 105, 5.0 105, 1.0 105, 0.0 g/L, respectively.
ð1Þ
where F and F0 represent the fluorescence intensities of QDs interact with and without CPZ–SBT, respectively. From the figure, DF of c and d was significantly greater than DF of a and b. Therefore, ZnS:Ni/ZnS was better as fluorescence probe for detecting CPZ–SBT. Recognition function of ZnS:Ni/ZnS probe to CPZ–SBT with different concentration Fig. 5 was fluorescence spectra of ZnS:Ni/ZnS and ZnS:Ni/ZnS interact with different concentrations of CPZ–SBT. From the figure, it was clearly that different concentrations of CPZ–SBT had different enhancement effects to fluorescence of ZnS:Ni/ZnS. Based on this, linear curve of CPZ–SBT could be established. Optimization of the conditions Effect of pH and buffer KH2PO4-K2HPO4, KH2PO4-sodium citric and citric acid-sodium citric were used to study the effect of buffer on the fluorescence
Fig. 6. Effect of pH.
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J. Qu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
Effect of ZnS:Ni/ZnS concentration ZnS:Ni/ZnS concentration directly affected to the fluorescence intensity of system (as shown in Fig. 7). It was found that there was a more higher DF with a concentration of ZnS:Ni/ZnS in the range from 0.12 to 1.44 mg/L. And the max of DF was at 0.48 mg/L. When exceeding 0.48 mg/L, DF decreased with the concentration increased. That was because that the reaction of two was completely at 0.48 mg/L. Thus, the optimum concentration was chosen to be 0.48 mg/L for this assay. Tolerance of foreign substance The influences of foreign substances, such as anions, cations, starch and glucose had been studied. The concentration ratios of the added foreign substance and substrates for a ±5% signal change were stipulated for a tolerable limit. The results were presented that the coexisting components were allowed maximum times 2 + amount were 200 times Na+, NHþ 4 , K , Cl , NO3 , SO4 , 25 times glucose and 10 times starch. This demonstrated that detecting CPZ–SBT based on ZnS:Ni/ZnS probe had good selectivity.
Fig. 7. Effect of ZnS:Ni/ZnS QDs concentration.
Calibration curve Under the optimal conditions, effect of different CPZ–SBT concentration on fluorescence intensity of ZnS:Ni/ZnS was investigated. Experiments showed that the value of DF increased linearly with CPZ–SBT concentration in the range from 8.0 106 to 1.0 104 g/L (as shown in Fig. 8). The linear equation was DF = 97.616 + 26.356C (r = 0.9986) with detection limit of 1.0 107 g/L. Compared with other reports, this method was more simple, sensitive and rapid with low limit detection, as shown in Table 1. Sample analysis Using this method, three practical samples came from commercial drugs were analyzed and the results were shown in Table 2. Clearly, the average recovery was 99.8%, which indicated the proposed method is more accurate. Fig. 8. Linear curve of CPZ–SBT.
Mechanism of the reaction intensity of ZnS:Ni/ZnS + CPZ–SBT system, respectively. Experiment results showed that different mediums could cause different influences to the fluorescence intensity, and 0.1 mol/L KH2PO4-K2HPO4 buffer solution (PBS) could cause fluorescence change greatly and was chosen as the optimal medium. Since having a substantial effect on DF for CPZ–SBT determination, the pH of the system was also examined. As shown in Fig. 6, the maximum DF was obtained at pH 6.0. Exceeding that, DF decreased with increase of pH, which was due to that enhancement of alkaline may lead to the change of CPZ–SBT structure [14].
From Fig. 1, it was obviously that ZnS:Ni/ZnS ODs were better dispersion in the presence of CPZ–SBT, and average diameter of ZnS:Ni/ZnS ODs became larger. Based on this, we could conclude that better dispersion could enhance the fluorescence intensity. On the other hand, average diameter enlargement for QDs was because that a new compound may be formed after interaction between ZnS:Ni/ZnS and CPZ–SBT. And, it was this new compound tocause the increase of the fluorescence intensity. That was to say, the enhancement of fluorescence intensity may be the result of two factors.
Table 1 Comparison to other methods. Reference
Linearly range (g/L)
LOD (g/L)
Recovery (%)
[3]
CPZ SBT
1.5 102–2.7 1.4 102–2.7
4.08 107 1.96 106
100.1 100.2
[4]
CPZ SBT
4.9 102–0.49 2.4 102–0.24
1.0 106 2.0 106
99.9 100.4
[6]
CPZ SBT
20.66–154.95 20.29–152.18
2.31 106 6.22 106
102.6 100.7
This method
CPZ–SBT
8.0 106–1.0 104
1.0 107
99.8
354
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concentration of CPZ–SBT, and an isobestic point appeared at 330 nm. This phenomena confirmed the above inferring.
Table 2 Sample analysis and recovery test. Added (g/L) 5
3.0 10 7.0 105 9.0 105
Found (g/L) 5
2.9 10 9.1 105 9.1 105
Recovery (%)
Average (%)
97.0 101.7 100.6
99.8
Conclusions Core/shell structure ZnS:Ni/ZnS QDs have been synthesized via water-soluble route. The QDs were water-soluble, non-toxic and stronger fluorescence intensity, and presence of CPZ–SBT could enhance its fluorescence intensity. Based on this, a novel method to determine CPZ–SBT was developed, which was rapid, sensitive with good selectivity and showed a broad application prospect. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 31000065) and Natural Science Research Project from the Education Department of Henan Province (No. 2011B180012). References
Fig. 9. UV–vis spectra of the ZnS:Ni/ZnS QDs (a) and after interacting with different concentration of CPZ–SBT (b and c).
The UV–vis spectra of ZnS:Ni/ZnS QDs before and after interacting with CPZ–SBT were shown in Fig. 9. From the figure, QDs absorbance was gradually increased after interacting with the rising
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Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Preparation of ZnS:Ni/ZnS quantum dots with core/shell structure and application for detecting cefoperazone–sulbactam Jianying Qu a,⇑, Zhuanying Zhu a, Changda Wu a, Lianjie Zhang a, Jianhang Qu b a b
Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, PR China College of Bioengineering, Henan University of Technology, Zhengzhou, Henan 450000, PR 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
ZnS:Ni/ZnS QDs were synthesized
easily with nontoxic. It shows fluorescent characteristic
with good water-solubility and stability. ZnS:Ni/ZnS QDs was firstly used as fluorescent probe to detect CPZ–SBT. This novel method is sensitive with good selectivity and a low detection limit.
a r t i c l e
i n f o
Article history: Received 27 August 2013 Received in revised form 25 October 2013 Accepted 31 October 2013 Available online 7 November 2013 Keywords: Cefoperazone Sulbactam Quantum dots
a b s t r a c t ZnS:Ni quantum dots (QDs) have been synthesized via a water-soluble route, which were coated by ZnS shell through surface modification to give ZnS:Ni/ZnS QDs. The QDs were characterized by atomic force microscope, X-ray diffraction, infrared spectrometry and fluorescent spectrometry. Then, a novel method for the determination of cefoperazone–sulbactam (CPZ–SBT) in aqueous solutions has been developed based on the enhancement of fluorescence of ZnS:Ni/ZnS QDs in the presence of CPZ–SBT. Under the optimal conditions, the enhanced fluorescence intensity (DF) was proportional to CPZ–SBT concentration in the range of 8.0 106–1.0 104 g/L with a detection limit of 1.0 107 g/L. The method was employed for the determination of CPZ–SBT in sample to give satisfactory result. Compared with others, this method was more sensitive, fast and simple with low limit detection. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Cefoperazone–sulbactam (CPZ–SBT) is a combination of antibiotics and enzyme inhibitor. Cefoperazone has B-lactam structure and sulbactam has semi-synthetic B-lactamase inhibitors, when used in combination, it can enhance antibacterial effect and antibacterial spectrum. And it has strong inhibitory effect against staphylococcus, b-lactamase, which were used for the treatment of various diseases [1,2]. At present, a few methods to determine CPZ–SBT have been reported mainly by high performance liquid ⇑ Corresponding author. Tel./fax: +86 0378 3881589. E-mail addresses: [email protected], [email protected] (J. Qu). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.096
chromatography (HPLC) [3–5] and ultra performance liquid chromatography (UPLC) [6]. Quantum dots (QDs) have attracted great interest due to their unique properties and potential applications in the past few decades. Recently, the applications of QDs in fluorescent probes [7], analysis and the detection [8], optical device [9] and fingerprint collection [10,11] are studied. Research showed that core/shell structure and alloy structure QDs could both significantly change the optical and electrical properties [12], which have attracted more and more attention. Here, ZnS:Ni/ZnS QDs with core/shell structure were prepared successfully. And based on the enhancement of fluorescence of ZnS:Ni/ZnS QDs in the presence of CPZ–SBT, a novel method to
J. Qu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
detect CPZ–SBT was established. Compared with other reports [3,4,6], this method was more simple, sensitive and rapid with low limit detection with potential prospect for practical applications.
351
were washed respectively by water and ethanol, and centrifuged. This operation was repeated for several times to remove impurities. Then the products were dried in a hot air oven at 65 °C for 5 h to obtain functionalized ZnS:Ni/ZnS QDs with approximate same size.
Experimental Results and discussions Apparatus Characterization of the ZnS:Ni/ZnS QDs SPA400 scanning probe microscope (Japan’s seiko), F-7000 spectrofluorometer (Japan’s Hitachi), VATAR360 type Fourier transformed infrared spectrometer (the United States, high-power company), UV-5400 UV spectrophotometer (American thermoelectric company), X-PertPro type X-ray diffraction (Dutch Philips), Phs-3 CT pH meter (Shanghai, Dapu instrument Co.), DF-101 Z water bath pot and DZF-250 vacuum drying oven (Zhengzhou, the Great Wall traded Co.) were used for experiments. Materials and reagents HSCH2COOH, NaOH (Tianjin Kemiou chemical reagent Co.), Zn(Ac)22H2O, Ni(Ac)24H2O, Na2S9H2O (Tianjin chemical reagent Co.), CPZ–SBT (Shandong runze pharmaceutical Co.), KH2PO4K2HPO4, KH2PO4-sodium citric, citric acid-sodium citric, and all other materials were analytical reagent grade. Doubly distilled water was used throughout. Synthesis of ZnS:Ni/ZnS QDs By modifying the synthesis methods reported [13], core/shell structure ZnS:Ni/ZnS QDs were obtained according to the following steps: 20 mL 0.1 mol/L of Zn(CH3COO)2, 2 mL 0.005 mol/L of Ni(CH3COO)2, 0.28 mL HSCH2COOH and 68 mL doubly distilled water were added into the three neck flask in turn and pH was adjusted to 11 with NaOH solution. The mixture was purged with N2 for 30 min. After being heated to 80 °C, 10 mL 0.1 mol/L of Na2S solution was added into the solution quickly with stirred magnetically and the mixture was stirred at 80 °C for 2 h. Then, 100 lL 1 mol/L of Zn(CH3COO)2, 12 lL HSCH2COOH, 25 lL 8 mol/L of NaOH and 25 lL 2 mol/L of Na2S were added respectively with stirred for 2 min. The above steps were repeated for 5 times. After 5 min, the proper amount of ethanol was added until a homogeneous solution was obtained. The obtained dispersions
Dynamic force microscope (DFM) characteristic Fig. 1a and b was DFM images of ZnS:Ni/ZnS QDs without and with CPZ–SBT. It was obviously that the synthetic ZnS:Ni/ZnS QDs were uniform with the average size of 60 nm. After interacting with CPZ–SBT, the diameter of ZnS:Ni/ZnS QDs became larger with the average size of about 70 nm. X-ray diffraction (XRD) characterization The XRD figures of ZnS, ZnS:Ni and ZnS:Ni/ZnS were obtained and shown in Fig. 2. It was clear that the three diffraction peaks for the three samples were appeared at the same positions, which were corresponding with the three peaks of ZnS (3 1 1), (2 2 0) and (1 1 1), respectively. Through comparison, Doping with Ni and further coating with ZnS shell did not change peak positions, intensity and number of ZnS, which demonstrated that ZnS:Ni/ZnS has the same crystal structure with ZnS [13]. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) characteristic ICP-AES was employed to test whether Ni existed in ZnS:Ni/ZnS QDs. The experimental results showed that Ni was doped into ZnS:Ni/ZnS successfully and the concentration of Ni in synthetic QDs was 0.301 mg/L. Therefore, the doping percentage of Ni in ZnS:Ni/ZnS was calculated of 1.0%. Infrared radiation (IR) characterization The IR spectra of CHCOOHSH (TGA) and ZnS:Ni/ZnS were shown in Fig. 3. Through comparing Fig. 3a and b, the peak of SAH of TGA at 2568 cm1 disappear for ZnS:Mn QDs, while peaks for C@O at 1581 cm1 and 1386 cm1 appeared. This demonstrated that TGA have combined with the surface of ZnS:Ni/ZnS QDs successfully through sulfydryl. Peak of C@O of ZnS:Ni/ZnS had a little hypochromatic shift due to substituent of C@O made change.
Fig. 1. DFM images of ZnS:Ni/ZnS QDs (a) and ZnS:Ni/ZnS QDs + CPZ–SBT (b).
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Fig. 2. XRD figures of ZnS (a), ZnS:Ni (b) and ZnS:Ni/ZnS (c).
Fig. 4. Fluorescence spectra of ZnS:Ni (a), ZnS:Ni + CPZ–SBT (b), ZnS:Ni/ZnS (c) and ZnS:Ni/ZnS + CPZ–SBT (d).
Fig. 3. IR spectra of TGA (a) and ZnS:Ni/ZnS QDs (b).
Fluorescence spectroscopy Fig. 4 was fluorescence spectra of ZnS:Ni, ZnS:Ni/ZnS in the absence and presence of CPZ–SBT, respectively. Fluorescence difference can be calculated by the formula:
DF ¼ F 0 F
Fig. 5. Fluorescence spectra of ZnS:Ni/ZnS and ZnS:Ni/ZnS interact with different concentrations of CPZ–SBT (a–d): 9.0 105, 5.0 105, 1.0 105, 0.0 g/L, respectively.
ð1Þ
where F and F0 represent the fluorescence intensities of QDs interact with and without CPZ–SBT, respectively. From the figure, DF of c and d was significantly greater than DF of a and b. Therefore, ZnS:Ni/ZnS was better as fluorescence probe for detecting CPZ–SBT. Recognition function of ZnS:Ni/ZnS probe to CPZ–SBT with different concentration Fig. 5 was fluorescence spectra of ZnS:Ni/ZnS and ZnS:Ni/ZnS interact with different concentrations of CPZ–SBT. From the figure, it was clearly that different concentrations of CPZ–SBT had different enhancement effects to fluorescence of ZnS:Ni/ZnS. Based on this, linear curve of CPZ–SBT could be established. Optimization of the conditions Effect of pH and buffer KH2PO4-K2HPO4, KH2PO4-sodium citric and citric acid-sodium citric were used to study the effect of buffer on the fluorescence
Fig. 6. Effect of pH.
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J. Qu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
Effect of ZnS:Ni/ZnS concentration ZnS:Ni/ZnS concentration directly affected to the fluorescence intensity of system (as shown in Fig. 7). It was found that there was a more higher DF with a concentration of ZnS:Ni/ZnS in the range from 0.12 to 1.44 mg/L. And the max of DF was at 0.48 mg/L. When exceeding 0.48 mg/L, DF decreased with the concentration increased. That was because that the reaction of two was completely at 0.48 mg/L. Thus, the optimum concentration was chosen to be 0.48 mg/L for this assay. Tolerance of foreign substance The influences of foreign substances, such as anions, cations, starch and glucose had been studied. The concentration ratios of the added foreign substance and substrates for a ±5% signal change were stipulated for a tolerable limit. The results were presented that the coexisting components were allowed maximum times 2 + amount were 200 times Na+, NHþ 4 , K , Cl , NO3 , SO4 , 25 times glucose and 10 times starch. This demonstrated that detecting CPZ–SBT based on ZnS:Ni/ZnS probe had good selectivity.
Fig. 7. Effect of ZnS:Ni/ZnS QDs concentration.
Calibration curve Under the optimal conditions, effect of different CPZ–SBT concentration on fluorescence intensity of ZnS:Ni/ZnS was investigated. Experiments showed that the value of DF increased linearly with CPZ–SBT concentration in the range from 8.0 106 to 1.0 104 g/L (as shown in Fig. 8). The linear equation was DF = 97.616 + 26.356C (r = 0.9986) with detection limit of 1.0 107 g/L. Compared with other reports, this method was more simple, sensitive and rapid with low limit detection, as shown in Table 1. Sample analysis Using this method, three practical samples came from commercial drugs were analyzed and the results were shown in Table 2. Clearly, the average recovery was 99.8%, which indicated the proposed method is more accurate. Fig. 8. Linear curve of CPZ–SBT.
Mechanism of the reaction intensity of ZnS:Ni/ZnS + CPZ–SBT system, respectively. Experiment results showed that different mediums could cause different influences to the fluorescence intensity, and 0.1 mol/L KH2PO4-K2HPO4 buffer solution (PBS) could cause fluorescence change greatly and was chosen as the optimal medium. Since having a substantial effect on DF for CPZ–SBT determination, the pH of the system was also examined. As shown in Fig. 6, the maximum DF was obtained at pH 6.0. Exceeding that, DF decreased with increase of pH, which was due to that enhancement of alkaline may lead to the change of CPZ–SBT structure [14].
From Fig. 1, it was obviously that ZnS:Ni/ZnS ODs were better dispersion in the presence of CPZ–SBT, and average diameter of ZnS:Ni/ZnS ODs became larger. Based on this, we could conclude that better dispersion could enhance the fluorescence intensity. On the other hand, average diameter enlargement for QDs was because that a new compound may be formed after interaction between ZnS:Ni/ZnS and CPZ–SBT. And, it was this new compound tocause the increase of the fluorescence intensity. That was to say, the enhancement of fluorescence intensity may be the result of two factors.
Table 1 Comparison to other methods. Reference
Linearly range (g/L)
LOD (g/L)
Recovery (%)
[3]
CPZ SBT
1.5 102–2.7 1.4 102–2.7
4.08 107 1.96 106
100.1 100.2
[4]
CPZ SBT
4.9 102–0.49 2.4 102–0.24
1.0 106 2.0 106
99.9 100.4
[6]
CPZ SBT
20.66–154.95 20.29–152.18
2.31 106 6.22 106
102.6 100.7
This method
CPZ–SBT
8.0 106–1.0 104
1.0 107
99.8
354
J. Qu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 350–354
concentration of CPZ–SBT, and an isobestic point appeared at 330 nm. This phenomena confirmed the above inferring.
Table 2 Sample analysis and recovery test. Added (g/L) 5
3.0 10 7.0 105 9.0 105
Found (g/L) 5
2.9 10 9.1 105 9.1 105
Recovery (%)
Average (%)
97.0 101.7 100.6
99.8
Conclusions Core/shell structure ZnS:Ni/ZnS QDs have been synthesized via water-soluble route. The QDs were water-soluble, non-toxic and stronger fluorescence intensity, and presence of CPZ–SBT could enhance its fluorescence intensity. Based on this, a novel method to determine CPZ–SBT was developed, which was rapid, sensitive with good selectivity and showed a broad application prospect. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 31000065) and Natural Science Research Project from the Education Department of Henan Province (No. 2011B180012). References
Fig. 9. UV–vis spectra of the ZnS:Ni/ZnS QDs (a) and after interacting with different concentration of CPZ–SBT (b and c).
The UV–vis spectra of ZnS:Ni/ZnS QDs before and after interacting with CPZ–SBT were shown in Fig. 9. From the figure, QDs absorbance was gradually increased after interacting with the rising
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