Synthesis of CdTe Semiconductor Nanocrystals on Hydrotalcite Matrix Surface for Electrochemical Detection of Ciprofloxacin
Authors: Sussuchi Eliana Midori , Carvalho Sanny W. M. M. , Gimenez Iara F. , SantAnna Mércia V. S. 
Published: February 2020

The synthesis of CdTe in the inorganic hydrotalcite matrix (LDH) was performed to form a hybrid material with synergistic properties to develop a sensitive and selective electrochemical method for the detection of ciprofloxacin (CPX). Despite its pharmacological relevance, CPX can be considered an emerging pollutant with known environmental effects [1-2], being found in μg L-1 to ng L-1 concentration ranges in both hospital and domestic effluents. For this reason, several analytical methods have been proposed for the determination of CPX [3-4]. Compared with other instrumental methods, electrochemistry fulfils such requirements with the possibility of electrode modification in order to become increasingly sensitive and selective to antibiotics [5-6]. Thus, the development of increasingly sensitive, novel low cost and simple electrochemical methods for CPX determination is highly desirable. The emission and absorption spectroscopies highlighted the growth of the CdTe semiconductor nanocrystals in the inorganic matrix [7]. Cyclic voltammetry confirmed the presence of CdTe grown in LDH (Figure 1a). The A1 oxidation peak (+0.35V) can be assigned to surface defects related to dangling bonds, while the other two peaks, A2 (+1.20V) and C1 (-1.32V) are assigned respectively to oxidation of the tellurium species in CdTe nanocrystals and the cathodic potential of refers to the reduction of oxidation products of metallic nature (CdTe + 6OH- → Cd2+ + TeO3
2- + 3H2O + 6e-). Carbon paste electrodes (CPE) and modified electrodes (MCPE) immobilizing LDH and synthesized hybrid (LDH/QD) were prepared for CPX detection (Figure 1b). The modified electrode obtained by the immobilization of LDH/QD presented better sensitivity for the detection of ciprofloxacin. The use of 20% in the paste composition at BR buffer (pH 6.0) during 300 s accumulation time and 20 mV s-1 scanning speed favored the analytical signal in terms of intensity and resolution. The analytical curve (Figure 1c) was determined from differential pulse voltammetry evidencing a linear behavior (R2 = 0.995) for CPX concentrations in the 2.5 x 10-8 – 1.2 x 10-5 mol L-1 range. The resulting equation was Ip,a(μA) = 3.00[CPX] – 7.00 x 10-5 where Ip,a refers to the anodic peak current, while [CPX] is concentration of ciprofloxacin. The limit of detection (LOD) was found to be 4.2 x 10-8 mol L-1 (three point three times the signal blank/slope) and limit of quantification (LOQ) was1.3 x 10-7 mol L-1 (ten times the signal blank/slope). In order to get information about the selectivity of MCPE/LDH-QD for CPX, an interference study was carried out in the presence of potential interferers (Zn2+, Fe2+, Cu2+, citric acid and ascorbic acid) using 0.1:1; 1:1; 10:1 interferer:CPX ratios. The CPX signal decreased in the presence of Zn2+, Fe2+ and Cu2+, with negligible effects for the low interferer concentrations. On the other hand, both citric and ascorbic acids interfered positively in CPX determination, since the current intensity increased slightly. A relative standard deviation (RSD) of 3.0% was found for CPX determination, indicating a remarkable reproducibility and precision, with 94% of recovery. The modified electrode was stored for two months at 4 °C, keeping the response at 95% of its initial value, suggesting that the MCPE-LDH/QD electrode is significantly stable. The method developed here was also applied to determine CPX in commercial 500 mg tablets. A certain weight of the tablet, milled and homogenized, was dissolved in 10 mL of ultrapure miliQ water. Ciprofloxacin was determined by the standard addition method and the result obtained (495 mg) is in agreement to the declared CPX content.

Acknowledgements: FAPITEC, CNPq, CAPES, Corrosion and Nanotechnology Laboratory – NUPEG and CLQM (Center of Chemistry Laboratories Multi-users) from Federal University of Sergipe for the analysis support.
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Figure 1