A simple, highly sensitive and stable electrochemical sensor for the detection of quercetin in solution, onion and honey buckwheat using zinc oxide supported on carbon nanosheet (ZnO/CNS/MCPE) modified carbon paste electrode

Quercetin is one of the most biologically active flavonols, and great attention has been paid for its detection in a variety of natural products over the few decades owing to its broad spectrum of applications. Herein, we have synthesized zinc oxide nanoparticles and carbon nanosheet separately, then the synthesized zinc oxide nanoparticles were dispersed uniformly into the carbon nanosheet, and finally, zinc oxide dispersed on carbon nanosheet modified carbon paste electrode (ZnO/CNS/MCPE) was fabricated. The prepared electrode is simple, highly sensitive, stable and cheaper for the detection of quercetin in standard solutions and real samples of onion and honey buckwheat. The scan rate optimization at ZnO/CNS/MCPE electrode showed electron-transfer co-efficient (alpha), electron-transfer number (n) and electrode reaction standard rate constants (Ks) as 1.13, 2.0 and 0.33 sec(-1) respectively. The electrochemical response for quercetin detection with ZnO/CNS/MCPE was greatly enhanced, which is about 8.0 times higher than the unmodified carbon paste electrode. The limit of detection and limit of quantification values were found to be 0.04 and 0.13 mu mol L-1 respectively. The relative standard deviation for the detection of 1.0 mmol L-1 quercetin in the standard solution for 10 successive cycles was found to be 1.76%. Compared to the other reported modified electrodes, the fabricated ZnO/CNS/MCPE has provided a superior electrochemical response, adequate selectivity and better sensitivity for the detection of quercetin in solution and real samples. (C) 2019 Elsevier Ltd. All rights reserved.