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Simple strategy for sensitive detection of dopamine using CdTe QDs modified glassy carbon electrode

Simple strategy for sensitive detection of dopamine using CdTe QDs modified glassy carbon electrode INTRODUCTIONDopamine, 3,4‐dihydroxyphenyl ethylamine, is a neurotransmitter of great importance for the nervous system of biological organisms, it is involved in motor control, endocrine function, reward, emotion, and cognition. Cellular and brain metabolism of dopamine can be correlated with a number of neurodegenerative disorders such as attention deficit hyperactivity disorder, mood disorders, Parkinson, and Alzheimer. The currently available analytical methods for dopamine determination in pharmaceutical samples and biological fluids including spectrophotometry, liquid chromatography, chemiluminescence, capillary electrophoresis, and electrochemical methods. However, aside from electrochemical detection, most of the procedures generally involve a time‐consuming sample pretreatment step and long analysis times and are relatively expensive. Therefore, the development of electrochemical biosensor has proven to be an attractive alternative for the determination of DA in the presence of interfering compounds due to their high sensitivity and selectivity, fast detection, low detection limits.Quantum dots (QDs), are semiconducting nanoparticlesas, that usually consist of group IIB‐VIB or IIIB‐VB elements and are diameter stable at 2‐20 nm, have exhibit excellent optical and electro‐optical properties due to their quantum size effect, surface effect, and dielectric confinement effect. As a novel member of carbon family, QDs have been widely used in bioanalytical research, however, numerous studies only focus on the optical research of QDs and ignored strong physical adsorption capacity, QDs possess a large number of hydroxyl and amino groups on the surface which can attract the electroactive compound dopamine. In this study, we fabricated a novel DA biosensor which was modified with CdTe QDs, the sensor showed high sensitivity and good reproducibility in determination of DA in human serum and urine samples with a high sensitivity and excellent selectivity.MATERIALS AND METHODSReagentsDopamine (C8H11NO2), Uric acid (C5H4N4O3, UA) and 3‐mercaptopropionic acid (3‐MPA) were purchased from Sigma (St. Loius, MO, USA). DA stock solution was prepared with phosphate buffer solution. A phosphate buffer was used to control the pH. Cadmium chloride (CdCl2 2.5H2O), sodium borohydride (NaBH4) and tellurium powder (Te) were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Other reagents were of analytical‐reagent grade and deionized water purified with Millipore system (Millipore Ltd. China) was used throughout this study. All experiments were conducted at the room temperature of 25°C human serum and urine samples were generously supplied by the first affiliated hospital of the Harbin Medical University. No. 23 Youzheng Street, Harbin, Heilongjiang Province, P. R. China.ApparatusThe cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were performed with a model CHI660C electrochemical workstation (Shanghai Chenhua Instruments Co. Shanghai, China). Electrochemical measurements were performed using a three‐electrode system consist of a platinum wire auxiliary electrode, an Ag/AgCl reference electrode and CdTe QDs modified electrode as working electrode (3 mm in diameter), (All from Incole Union Technology Co. Ltd, Tianjin, China). Solution pH was measured on pH meter (from Precision Scientific Instruments Co. Shanghai, China). Images of the CdTe QDs were observed using JEM‐2100 transmission electron microscope was purchased from Japan Electron Optics Laboratory Co. (JEOL, Japan). Ultrasonic cleaning machine was purchased from Kunshang. Co. Ltd. (Jiangsu, China).Preparation of CdTe QDs and modified electrodeAccording to the literature the molar ratio of Cd2+/MPA/Te− was optimized for 1:2.5:0.5. Tellurium powder was selected as a source of tellurium to synthetic the tellurium sodium hydride (NaHTe). 435.7 μL MPA solution were piped into 100 mL of 2.0 × 10−2 mol L−1 CdCl2 solution, then were sufficiently stirred with a magnetic stirrer, the solution was adjusted with 1 mol L−1 NaOH to pH 10.5. The following, the fresh 1 mmol L−1 NaHTe solution was slowly poured into it with stirring drastically under N2 and then heated to reflux at 100°C for 6 hours. Then, the QDs solution was purified by ethanol and separated by centrifugation at a 6700 g for three times. Finally, 0.1 g of the precipitate was re‐dissolved 50 mL in ultrapure water and preserved at 4°C in dark.The bare electrode was polished into a mirror with 0.3 and 0.05 μm alumina powder, rinsed with double distilled water, washed ultrasonically for 5 minutes in anhydrous ethanol and double distilled water in turn, then dried in N2. A 5 μL amount of CdTe QDs was dropped on the bare electrode surface to prepare the CdTe QDs/GCE then were dried in a 4°C N2 incubator. Finally, unattached CdTe QDs on the modified electrode surface were cleaned before used.RESULTSCharacterization of CdTe QDsTransmission electron microscopy (TEM) was employed to characterize the morphology of the prepared MPA‐capped QDs. Figure  shows the TEM micrograph of CdTe QDs dispersed uniformly with spherical shape and the size of the particles ranges between 3‐5 nm. CdTe QDs can be preserved for 3 months at 4°C in the dark and exhibit high stability.TEM image of CdTe QDsFigure A shows the cyclic voltammograms of the bare electrode and the CdTe QDs/GCE in 200 μmol L−1 DA solution at the scanning rate of 100 mV/s. As it is seen, the anodic peak current of DA on CdTe QDs/GCE is much higher than bare GCE, indicating CdTe QDs/GCE has the excellent electrochemical activity. Figure B depicts the electrochemical impedance spectra of bare GCE (a), CdTe QDs/GCE (b) in presence of equimolar 5 mmol L−1 K3Fe(CN)6 + 5 mmol L−1 K4Fe(CN)6 + 0.1 mol L−1 KCl. The charge transfer resistance (RCT) values were determined directly from the diameters of the high frequency semicircle. The diameter of the semicircle for CdTe QDs/GCE was larger than that of bare GCE, indicating that the CdTe QDs on the surface of GCE increased the electron transfer rate between the redox probe of the electrode surface and [Fe(CN)6]3−/4−. Plenty of polar and negatively charged oxygen functional groups such as ‐COOH and ‐OH prevent [Fe(CN)6]3−/4− from penetrating the electrode/solution interference.(A) shows the cyclic voltammograms of the bare electrode and the CdTe QDs/GCE in 200 μmol L−1 DA solution. (B) depicts the electrochemical impedance spectra of bare GCE (a), CdTe QDs/GCE (b)Effect of buffer pHThe effect of pH on the electrochemical response of DA attached to CdTe QDs modified electrode were examined by DPV within a pH range of 4.0‐9.0 (Figure ). It is clearly found that the peak currents of DA are pH‐dependent, which indicated that protons can participate in the electrochemical reaction of DA. According to the results, the maximum value appeared at pH 7.5 which was selected as optimal pH for the electrochemical detection in all subsequent studies.Effect of pH on DPV peak current in 0.01 μmol L−1 containing 300 μmol L−1 DA (pH from a to g: 4, 5, 6, 7, 7.5, 8, 9)Electrochemical propertiesThe mechanism of the proposed CdTe QDs/GCE have higher sensitivity and selectivity for DA detection is that CdTe QDs possess a large number of hydroxyl groups on the surface which can combine the amino on dopamine. Figure  A presents DPV response of CdTe QDs/GCE in various of concentrations of DA. The DPV responses of the CdTe QDs/GCE electrode after incubation in a DA solution of concentration ranging from 5 μmol L−1 to 200 μmol L−1 in a pH = 7.5 buffer shows that the peak current increases as the increase in DA concentration. As shown in Figure B, this linear regression equation was described as Ipa(μA) = 0.178C + 0.866, C is concentration, R2 = 0.992. giving a detection limit of 0.3 μmol L−1, based on signal‐to‐noise ratio of 3 (S/N = 3). Comparisons of this sensor with other chemically modified electrodes are listed in Table . The excellent electro‐catalytic ability of the modified electrode is attributed to the large number of carboxylic groups on the surface of CdTe QDs that can effectively interact with DA.(A) DPV response to 200 μmol L−1, 180, 150, 120, 100, 80, 50, 30, 20, 10, 5 μmol L−1 of DA (from a to k) and (B) calibration plot of DPV peak current vs target DA concentrationComparison of electro analytical parameters for the determination of DA at CdTe QDs modified electrode with other reported modified electrodesElectroDetection limit (μmol L−1)Linear range (μmol L−1)Ref.GR‐CS composite0.00450.03‐20.06PEDOT/Pd composite0.50.5‐1.0PPy‐rGOc10.01‐10Tyrosinase/NiO/ITO1.0382‐100AuNP‐PAH0.260.49‐23.0CdTe0.31‐400This workInterferenceDue to its coexistence with DA, UA in biological samples, herein, we first studied the interference of UA on the detection of 200 μmol L−1 DA at the CdTe QDs modified electrode. The oxidation peak currents and potentials of DA was not affected in the presence of UA (Figure ). Also, we examined the interference of AA and glucose on the detection of 200 μmol L−1 DA, the results showed that there is no effect on the determination of DA up to 300 μmol L−1 AA and 200 μmol L−1 glucose. These results demonstrate that the CdTe QDs modified GCE possesses excellent selectivity.DPV profiles at the CdTe QDs modified GCE in PBS buffer (pH 7.5) containing (A) 200 μmol L−1 DA and different concentrations of UA (from bottom to top: 100 μmol L−1, 120 μmol L−1 and 150 μmol L−1 UA)Analysis of DA in real life samplesIn order to evaluate the applicability of the proposed sensor, the concentration limit of DA in human serum and urine samples were determined by applying the standard addition method. The serum and urine samples were diluted 15 times with PBS (pH = 7.5) before measurement. The analytical results were showed in Table . The recovery was in the range of 99.07%‐101.75%. The RSD value is less than 4%, demonstrating that the obtained CdTe QDs modified GCE can be used precisely for DA detection in real samples.Determination of DA in human serum and urine samples at CdTe QDs modified electrodeSampleAdded (μmol L−1)Found (μmol L−1)Recovery (%)RSD (%)Serum10099.5999.592.53150152.63101.753.88200202.5101.252.86Urine10099.0799.072.61150151.5101.002.18200200.57100.293.63RSD value reported is for n = 3.Reproducibility and stability studiesThe reproducibility of the biosensor was investigated by repetitive measurements of DA oxidation peak currents in presence of 200 μmol L−1 DA solution in PBS. Five parallel measurements of DA were carried out, the relative standard deviation is 4.3%. indicating that the CdTe QDs modified electrode has good reproducibility. Meanwhile, CdTe QDs/GCE were used intermittently and stored for 2 weeks in order to examine the stability of the modified electrode, the current signals could show a less than 5% decrease relative to the initial response indicating that the obtained CdTe QDs can show an excellent stability of the proposed modified electrode.CONCLUSIONSIn this paper, the proposed electrochemical biosensor was established by a easy strategy and exhibited good analytical performance in the determination of DA. The promising results obtained in this study suggest that the excellent analytical performance of the proposed method is due to the efficient immobilization of CdTe QDs. With the good selectivity and practicability, the proposed method has been applied to the determination of DA in real samples with satisfactory results. The fabricated sensor may provided a new electrochemical method for clinical diagnosis in the future.ACKNOWLEDGMENTSThis study was supported by the National Natural Science Foundation of China No. 81573200, No. 81373047, No. 81273129 and Foundation of outstanding leaders training program of Pudong Health Bureau of Shanghai (Grant No.PWRI2016‐04). The authors greatly appreciated these supports.REFERENCESJiang Y, Wang B, Meng F, Cheng Y, Zhu C. Microwave‐assisted preparation of N‐doped carbon dots as a biosensor for electrochemical dopamine detection. J Colloid Interface Sci. 2015;452:199‐202.Goyal RN, Bishnoi S. Simultaneous determination of epinephrine and norepinephrine in human blood plasma and urine samples using nanotubes modified edge plane pyrolytic graphite electrode. Talanta. 2011;84:78‐83.Silva TR, Vieira IC. A biosensor based on gold nanoparticles stabilized in poly(allylamine hydrochloride) and decorated with laccase for determination of dopamine. Analyst. 2016;141:216‐224.Ali SR, Ma Y, Parajuli RR, Balogun Y, Lai WY, He H. A nonoxidative sensor based on a self‐doped polyaniline/carbon nanotube composite for sensitive and selective detection of the neurotransmitter dopamine. Anal Chem. 2007;79:2583‐2587.Solich P, Polydorou CK, Koupparis MA, Efstathiou CE. Automated flow‐injection spectrophotometric determination of catecholamines (epinephrine and isoproterenol) in pharmaceutical formulations based on ferrous complex formation. J Pharm Biomed Anal. 2000;22:781‐789.Li Q, Li J, Yang Z. Study of the sensitization of tetradecyl benzyl dimethyl ammonium chloride for spectrophotometric determination of dopamine hydrochloride using sodium 1,2‐naphthoquinone‐4‐sulfonate as the chemical derivative chromogenic reagent. Anal Chim Acta. 2007;583:147‐152.Chen JL, Yan XP, Meng K, Wang SF. Graphene oxide based photoinduced charge transfer label‐free near‐infrared fluorescent biosensor for dopamine. Anal Chem. 2011;83:8787‐8793.Wei S, Song G, Lin JM. Separation and determination of norepinephrine, epinephrine and isoprinaline enantiomers by capillary electrophoresis in pharmaceutical formulation and human serum. J Chromatogr A. 2005;1098:166‐171.Raghu P, Reddy TM, Gopal P, Reddaiah K, Sreedhar NY. A novel horseradish peroxidase biosensor towards the detection of dopamine: a voltammetric study. Enzyme Microb Technol. 2014;57:8‐15.Bruchez M Jr, Moronne M, Gin P, Weiss S, Alivisatos AP. Semiconductor nanocrystals as fluorescent biological labels. Science. 1998;281:2013‐2016.Yu C, Yan J, Tu Y. Electrochemiluminescent sensing of dopamine using CdTe quantum dots capped with thioglycolic acid and supported with carbon nanotubes. Microchim Acta. 2011;175:347.Zhang G, Shi L, Selke M, Wang X. CdTe quantum dots with daunorubicin induce apoptosis of multidrug‐resistant human hepatoma HepG2/ADM cells: in vitro and in vivo evaluation. Nanoscale Res Lett. 2011;6:418‐428.Li M, Ge Y, Chen Q, Xu S, Wang N, Zhang X. Hydrothermal synthesis of highly luminescent CdTe quantum dots by adjusting precursors' concentration and their conjunction with BSA as biological fluorescent probes. Talanta. 2007;72:89‐94.Pan D, Rong S, Zhang G, et al. Electrochemical determination of uric acid at CdTe quantum dot modified glassy carbon electrodes. J AOAC Int. 2015;98:1260‐1266.Palanisamy S, Thangavelu K, Chen SM, Gnanaprakasam P, Velusamy V, Liu XH. Preparation of chitosan grafted graphite composite for sensitive detection of dopamine in biological samples. Carbohydr Polym. 2016;151:401‐407.Harish S, Mathiyarasu J, Phani KLN, Yegnaraman V. PEDOT/Palladium composite material: synthesis, characterization and application to simultaneous determination of dopamine and uric acid. J Appl Electrochem. 2008;38:1583‐1588.Qian T, Wu S, Shen J. Facilely prepared polypyrrole‐reduced graphite oxide core‐shell microspheres with high dispersibility for electrochemical detection of dopamine. Chem Commun (Camb). 2013;49:4610‐4612.Roychoudhury A, Basu S, Jha SK. Dopamine biosensor based on surface functionalized nanostructured nickel oxide platform. Biosens Bioelectron. 2016;84:72‐81. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Clinical Laboratory Analysis Wiley

Simple strategy for sensitive detection of dopamine using CdTe QDs modified glassy carbon electrode

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Wiley
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Copyright © 2018 Wiley Periodicals, Inc.
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0887-8013
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1098-2825
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10.1002/jcla.22320
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28940690
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Abstract

INTRODUCTIONDopamine, 3,4‐dihydroxyphenyl ethylamine, is a neurotransmitter of great importance for the nervous system of biological organisms, it is involved in motor control, endocrine function, reward, emotion, and cognition. Cellular and brain metabolism of dopamine can be correlated with a number of neurodegenerative disorders such as attention deficit hyperactivity disorder, mood disorders, Parkinson, and Alzheimer. The currently available analytical methods for dopamine determination in pharmaceutical samples and biological fluids including spectrophotometry, liquid chromatography, chemiluminescence, capillary electrophoresis, and electrochemical methods. However, aside from electrochemical detection, most of the procedures generally involve a time‐consuming sample pretreatment step and long analysis times and are relatively expensive. Therefore, the development of electrochemical biosensor has proven to be an attractive alternative for the determination of DA in the presence of interfering compounds due to their high sensitivity and selectivity, fast detection, low detection limits.Quantum dots (QDs), are semiconducting nanoparticlesas, that usually consist of group IIB‐VIB or IIIB‐VB elements and are diameter stable at 2‐20 nm, have exhibit excellent optical and electro‐optical properties due to their quantum size effect, surface effect, and dielectric confinement effect. As a novel member of carbon family, QDs have been widely used in bioanalytical research, however, numerous studies only focus on the optical research of QDs and ignored strong physical adsorption capacity, QDs possess a large number of hydroxyl and amino groups on the surface which can attract the electroactive compound dopamine. In this study, we fabricated a novel DA biosensor which was modified with CdTe QDs, the sensor showed high sensitivity and good reproducibility in determination of DA in human serum and urine samples with a high sensitivity and excellent selectivity.MATERIALS AND METHODSReagentsDopamine (C8H11NO2), Uric acid (C5H4N4O3, UA) and 3‐mercaptopropionic acid (3‐MPA) were purchased from Sigma (St. Loius, MO, USA). DA stock solution was prepared with phosphate buffer solution. A phosphate buffer was used to control the pH. Cadmium chloride (CdCl2 2.5H2O), sodium borohydride (NaBH4) and tellurium powder (Te) were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Other reagents were of analytical‐reagent grade and deionized water purified with Millipore system (Millipore Ltd. China) was used throughout this study. All experiments were conducted at the room temperature of 25°C human serum and urine samples were generously supplied by the first affiliated hospital of the Harbin Medical University. No. 23 Youzheng Street, Harbin, Heilongjiang Province, P. R. China.ApparatusThe cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were performed with a model CHI660C electrochemical workstation (Shanghai Chenhua Instruments Co. Shanghai, China). Electrochemical measurements were performed using a three‐electrode system consist of a platinum wire auxiliary electrode, an Ag/AgCl reference electrode and CdTe QDs modified electrode as working electrode (3 mm in diameter), (All from Incole Union Technology Co. Ltd, Tianjin, China). Solution pH was measured on pH meter (from Precision Scientific Instruments Co. Shanghai, China). Images of the CdTe QDs were observed using JEM‐2100 transmission electron microscope was purchased from Japan Electron Optics Laboratory Co. (JEOL, Japan). Ultrasonic cleaning machine was purchased from Kunshang. Co. Ltd. (Jiangsu, China).Preparation of CdTe QDs and modified electrodeAccording to the literature the molar ratio of Cd2+/MPA/Te− was optimized for 1:2.5:0.5. Tellurium powder was selected as a source of tellurium to synthetic the tellurium sodium hydride (NaHTe). 435.7 μL MPA solution were piped into 100 mL of 2.0 × 10−2 mol L−1 CdCl2 solution, then were sufficiently stirred with a magnetic stirrer, the solution was adjusted with 1 mol L−1 NaOH to pH 10.5. The following, the fresh 1 mmol L−1 NaHTe solution was slowly poured into it with stirring drastically under N2 and then heated to reflux at 100°C for 6 hours. Then, the QDs solution was purified by ethanol and separated by centrifugation at a 6700 g for three times. Finally, 0.1 g of the precipitate was re‐dissolved 50 mL in ultrapure water and preserved at 4°C in dark.The bare electrode was polished into a mirror with 0.3 and 0.05 μm alumina powder, rinsed with double distilled water, washed ultrasonically for 5 minutes in anhydrous ethanol and double distilled water in turn, then dried in N2. A 5 μL amount of CdTe QDs was dropped on the bare electrode surface to prepare the CdTe QDs/GCE then were dried in a 4°C N2 incubator. Finally, unattached CdTe QDs on the modified electrode surface were cleaned before used.RESULTSCharacterization of CdTe QDsTransmission electron microscopy (TEM) was employed to characterize the morphology of the prepared MPA‐capped QDs. Figure  shows the TEM micrograph of CdTe QDs dispersed uniformly with spherical shape and the size of the particles ranges between 3‐5 nm. CdTe QDs can be preserved for 3 months at 4°C in the dark and exhibit high stability.TEM image of CdTe QDsFigure A shows the cyclic voltammograms of the bare electrode and the CdTe QDs/GCE in 200 μmol L−1 DA solution at the scanning rate of 100 mV/s. As it is seen, the anodic peak current of DA on CdTe QDs/GCE is much higher than bare GCE, indicating CdTe QDs/GCE has the excellent electrochemical activity. Figure B depicts the electrochemical impedance spectra of bare GCE (a), CdTe QDs/GCE (b) in presence of equimolar 5 mmol L−1 K3Fe(CN)6 + 5 mmol L−1 K4Fe(CN)6 + 0.1 mol L−1 KCl. The charge transfer resistance (RCT) values were determined directly from the diameters of the high frequency semicircle. The diameter of the semicircle for CdTe QDs/GCE was larger than that of bare GCE, indicating that the CdTe QDs on the surface of GCE increased the electron transfer rate between the redox probe of the electrode surface and [Fe(CN)6]3−/4−. Plenty of polar and negatively charged oxygen functional groups such as ‐COOH and ‐OH prevent [Fe(CN)6]3−/4− from penetrating the electrode/solution interference.(A) shows the cyclic voltammograms of the bare electrode and the CdTe QDs/GCE in 200 μmol L−1 DA solution. (B) depicts the electrochemical impedance spectra of bare GCE (a), CdTe QDs/GCE (b)Effect of buffer pHThe effect of pH on the electrochemical response of DA attached to CdTe QDs modified electrode were examined by DPV within a pH range of 4.0‐9.0 (Figure ). It is clearly found that the peak currents of DA are pH‐dependent, which indicated that protons can participate in the electrochemical reaction of DA. According to the results, the maximum value appeared at pH 7.5 which was selected as optimal pH for the electrochemical detection in all subsequent studies.Effect of pH on DPV peak current in 0.01 μmol L−1 containing 300 μmol L−1 DA (pH from a to g: 4, 5, 6, 7, 7.5, 8, 9)Electrochemical propertiesThe mechanism of the proposed CdTe QDs/GCE have higher sensitivity and selectivity for DA detection is that CdTe QDs possess a large number of hydroxyl groups on the surface which can combine the amino on dopamine. Figure  A presents DPV response of CdTe QDs/GCE in various of concentrations of DA. The DPV responses of the CdTe QDs/GCE electrode after incubation in a DA solution of concentration ranging from 5 μmol L−1 to 200 μmol L−1 in a pH = 7.5 buffer shows that the peak current increases as the increase in DA concentration. As shown in Figure B, this linear regression equation was described as Ipa(μA) = 0.178C + 0.866, C is concentration, R2 = 0.992. giving a detection limit of 0.3 μmol L−1, based on signal‐to‐noise ratio of 3 (S/N = 3). Comparisons of this sensor with other chemically modified electrodes are listed in Table . The excellent electro‐catalytic ability of the modified electrode is attributed to the large number of carboxylic groups on the surface of CdTe QDs that can effectively interact with DA.(A) DPV response to 200 μmol L−1, 180, 150, 120, 100, 80, 50, 30, 20, 10, 5 μmol L−1 of DA (from a to k) and (B) calibration plot of DPV peak current vs target DA concentrationComparison of electro analytical parameters for the determination of DA at CdTe QDs modified electrode with other reported modified electrodesElectroDetection limit (μmol L−1)Linear range (μmol L−1)Ref.GR‐CS composite0.00450.03‐20.06PEDOT/Pd composite0.50.5‐1.0PPy‐rGOc10.01‐10Tyrosinase/NiO/ITO1.0382‐100AuNP‐PAH0.260.49‐23.0CdTe0.31‐400This workInterferenceDue to its coexistence with DA, UA in biological samples, herein, we first studied the interference of UA on the detection of 200 μmol L−1 DA at the CdTe QDs modified electrode. The oxidation peak currents and potentials of DA was not affected in the presence of UA (Figure ). Also, we examined the interference of AA and glucose on the detection of 200 μmol L−1 DA, the results showed that there is no effect on the determination of DA up to 300 μmol L−1 AA and 200 μmol L−1 glucose. These results demonstrate that the CdTe QDs modified GCE possesses excellent selectivity.DPV profiles at the CdTe QDs modified GCE in PBS buffer (pH 7.5) containing (A) 200 μmol L−1 DA and different concentrations of UA (from bottom to top: 100 μmol L−1, 120 μmol L−1 and 150 μmol L−1 UA)Analysis of DA in real life samplesIn order to evaluate the applicability of the proposed sensor, the concentration limit of DA in human serum and urine samples were determined by applying the standard addition method. The serum and urine samples were diluted 15 times with PBS (pH = 7.5) before measurement. The analytical results were showed in Table . The recovery was in the range of 99.07%‐101.75%. The RSD value is less than 4%, demonstrating that the obtained CdTe QDs modified GCE can be used precisely for DA detection in real samples.Determination of DA in human serum and urine samples at CdTe QDs modified electrodeSampleAdded (μmol L−1)Found (μmol L−1)Recovery (%)RSD (%)Serum10099.5999.592.53150152.63101.753.88200202.5101.252.86Urine10099.0799.072.61150151.5101.002.18200200.57100.293.63RSD value reported is for n = 3.Reproducibility and stability studiesThe reproducibility of the biosensor was investigated by repetitive measurements of DA oxidation peak currents in presence of 200 μmol L−1 DA solution in PBS. Five parallel measurements of DA were carried out, the relative standard deviation is 4.3%. indicating that the CdTe QDs modified electrode has good reproducibility. Meanwhile, CdTe QDs/GCE were used intermittently and stored for 2 weeks in order to examine the stability of the modified electrode, the current signals could show a less than 5% decrease relative to the initial response indicating that the obtained CdTe QDs can show an excellent stability of the proposed modified electrode.CONCLUSIONSIn this paper, the proposed electrochemical biosensor was established by a easy strategy and exhibited good analytical performance in the determination of DA. The promising results obtained in this study suggest that the excellent analytical performance of the proposed method is due to the efficient immobilization of CdTe QDs. With the good selectivity and practicability, the proposed method has been applied to the determination of DA in real samples with satisfactory results. The fabricated sensor may provided a new electrochemical method for clinical diagnosis in the future.ACKNOWLEDGMENTSThis study was supported by the National Natural Science Foundation of China No. 81573200, No. 81373047, No. 81273129 and Foundation of outstanding leaders training program of Pudong Health Bureau of Shanghai (Grant No.PWRI2016‐04). The authors greatly appreciated these supports.REFERENCESJiang Y, Wang B, Meng F, Cheng Y, Zhu C. Microwave‐assisted preparation of N‐doped carbon dots as a biosensor for electrochemical dopamine detection. J Colloid Interface Sci. 2015;452:199‐202.Goyal RN, Bishnoi S. Simultaneous determination of epinephrine and norepinephrine in human blood plasma and urine samples using nanotubes modified edge plane pyrolytic graphite electrode. Talanta. 2011;84:78‐83.Silva TR, Vieira IC. A biosensor based on gold nanoparticles stabilized in poly(allylamine hydrochloride) and decorated with laccase for determination of dopamine. Analyst. 2016;141:216‐224.Ali SR, Ma Y, Parajuli RR, Balogun Y, Lai WY, He H. A nonoxidative sensor based on a self‐doped polyaniline/carbon nanotube composite for sensitive and selective detection of the neurotransmitter dopamine. Anal Chem. 2007;79:2583‐2587.Solich P, Polydorou CK, Koupparis MA, Efstathiou CE. Automated flow‐injection spectrophotometric determination of catecholamines (epinephrine and isoproterenol) in pharmaceutical formulations based on ferrous complex formation. J Pharm Biomed Anal. 2000;22:781‐789.Li Q, Li J, Yang Z. Study of the sensitization of tetradecyl benzyl dimethyl ammonium chloride for spectrophotometric determination of dopamine hydrochloride using sodium 1,2‐naphthoquinone‐4‐sulfonate as the chemical derivative chromogenic reagent. Anal Chim Acta. 2007;583:147‐152.Chen JL, Yan XP, Meng K, Wang SF. Graphene oxide based photoinduced charge transfer label‐free near‐infrared fluorescent biosensor for dopamine. Anal Chem. 2011;83:8787‐8793.Wei S, Song G, Lin JM. Separation and determination of norepinephrine, epinephrine and isoprinaline enantiomers by capillary electrophoresis in pharmaceutical formulation and human serum. J Chromatogr A. 2005;1098:166‐171.Raghu P, Reddy TM, Gopal P, Reddaiah K, Sreedhar NY. A novel horseradish peroxidase biosensor towards the detection of dopamine: a voltammetric study. Enzyme Microb Technol. 2014;57:8‐15.Bruchez M Jr, Moronne M, Gin P, Weiss S, Alivisatos AP. Semiconductor nanocrystals as fluorescent biological labels. Science. 1998;281:2013‐2016.Yu C, Yan J, Tu Y. Electrochemiluminescent sensing of dopamine using CdTe quantum dots capped with thioglycolic acid and supported with carbon nanotubes. Microchim Acta. 2011;175:347.Zhang G, Shi L, Selke M, Wang X. CdTe quantum dots with daunorubicin induce apoptosis of multidrug‐resistant human hepatoma HepG2/ADM cells: in vitro and in vivo evaluation. Nanoscale Res Lett. 2011;6:418‐428.Li M, Ge Y, Chen Q, Xu S, Wang N, Zhang X. Hydrothermal synthesis of highly luminescent CdTe quantum dots by adjusting precursors' concentration and their conjunction with BSA as biological fluorescent probes. Talanta. 2007;72:89‐94.Pan D, Rong S, Zhang G, et al. Electrochemical determination of uric acid at CdTe quantum dot modified glassy carbon electrodes. J AOAC Int. 2015;98:1260‐1266.Palanisamy S, Thangavelu K, Chen SM, Gnanaprakasam P, Velusamy V, Liu XH. Preparation of chitosan grafted graphite composite for sensitive detection of dopamine in biological samples. Carbohydr Polym. 2016;151:401‐407.Harish S, Mathiyarasu J, Phani KLN, Yegnaraman V. PEDOT/Palladium composite material: synthesis, characterization and application to simultaneous determination of dopamine and uric acid. J Appl Electrochem. 2008;38:1583‐1588.Qian T, Wu S, Shen J. Facilely prepared polypyrrole‐reduced graphite oxide core‐shell microspheres with high dispersibility for electrochemical detection of dopamine. Chem Commun (Camb). 2013;49:4610‐4612.Roychoudhury A, Basu S, Jha SK. Dopamine biosensor based on surface functionalized nanostructured nickel oxide platform. Biosens Bioelectron. 2016;84:72‐81.

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Published: Jan 1, 2018

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