A new nanocomposite based on ZnCdTe semiconductor nanocrystals (NCs) synthesized in situ on reduced graphene oxide (rGO) was obtained. The heterostructure was characterized using UV-Vis emission and absorption spectroscopies, which provided evidences of the growth of the nanocrystals onto the rGO matrix. To evaluate the electrochemical performance, carbon paste electrodes modified with the nanocomposite (QD-rGO/CPE) were prepared, showing high sensitivity in the electroanalytical detection of the pesticide carbendazim. Under optimal operational conditions a calibration curve was constructed with a linear behavior in the range of 9.98 × 10 -8 to 1.18 × 10 -5 mol L -1 , with a correlation coefficient of 0.997. The limit of detection (LOD) and the limit of quantification (LOQ) for carbendazim were 9.16 × 10 -8 and 2.78 × 10 -7 mol L -1 , respectively. The electrode is successfully applied for the determination of carbendazim in orange juice samples.
In this work, CdTe quantum dots (QDs) were controllably grown onto the surface of layered double hydroxide (LDH) aiming to develop a sensitive and selective method for the electrochemical detection of ciprofloxacin (CPX). Emission and absorption spectroscopy results as well as high-resolution transmission electron microscopy (HRTEM) images evidenced the formation of LDH/QD hybrid material. Unmodified carbon paste electrodes (CPE) as well as CPE chemically modified (MCPE) with native LDH and with the LDH/QD hybrid were prepared for CPX detection, revealing that MCPE-LDH/QD had the highest sensitivity for the detection of ciprofloxacin. Optimum detection conditions included a modifier dosage of 20% in MCPE, Britton-Robinson (BR) buffer (pH 6.0) as analytical medium, 300 s accumulation time and a scanning rate of 20 mV s-1. Linear current versus concentration curve was observed from 2.5 × 10-8-1.2 × 10-5 mol L-1 (coefficient of determination (R 2) = 0.995), with sensitivity (limit of detection (LOD) = 4.2 × 10-8 mol L-1 ; limit of quantification (LOQ) = 1.3 × 10-7 mol L-1), precision (relative standard deviation (RSD) = 3.0%), accuracy (94.0%) and satisfactory selectivity in the presence of Zn 2+ , Fe 2+ , Cu 2+ , citric acid and ascorbic acid. Tests of CPX determination in commercial 500 mg ciprofloxacin tablets evidenced the applicability of the method.
This work describes the synthesis of a glutathione-capped Cd 1-x Mg x Te semiconductor nanocrystal alloy in aqueous solution. The effects of reaction time and Cd:Mg molar proportion on the spectroscopic and electrochemical properties were optimized. The Cd 1-x Mg x Te material was found to emit in the visible range (blueishgreen to dark pink), with the band gap energy depending both on the Mg:Cd ratio and of the nanocrystal size. The insitu growth of the nanocrystal alloy on both graphene oxide and reduced graphene oxide leads to partial quenching of the photoluminescence of Cd 1-x Mg x Te but improves the electrochemical response of the nanocrystals. Carbon paste electrodes (CPE) were modified with the graphene-based materials containing semiconductor nanocrystals, and it is shown that such a modified CPE can be applied to the determination of the local anesthetic lidocaine and the anaphylactic drug epinephrine via differential pulse voltammetry. Each analyte can be determined both individually and in the presence of constant concentrations of the other, best at typical oxidation potentials of 0.25 V and 1.0 V (vs. Ag/ AgCl), respectively. In the best cases, the detection limits are 92 nM for lidocaine and 0.95 μM for epinephrine.
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