A ZnO quantum dot/Nafion modified voltammetric sensor for sensitive determination of cadmium and lead in food samples

Abstract

Zinc oxide quantum dots (ZnO QDs) have attracted considerable attention as advanced nanomaterials for electrochemical sensing due to their large specific surface area, good electrical conductivity, and strong affinity for metal ion adsorption. These characteristics can significantly enhance the sensitivity and selectivity of electrochemical detection. In this study, a differential pulse anodic stripping voltammetry (DPASV) method was developed for the simultaneous determination of Cd²⁺ and Pb²⁺ in food samples using a gold electrode modified with a ZnO QDs/Nafion nanocomposite film. ZnO QDs were synthesized via a sol–gel method by reacting zinc acetate with potassium hydroxide in ethanol under controlled temperature and continuous stirring. The fabricated electrode was characterized in terms of surface morphology, electrochemical behavior, and analytical performance toward Pb²⁺ and Cd²⁺ detection. The optimal electroanalytical conditions were as follows: acetate buffer (pH 5.0), deposition time of 90 s, pulse amplitude of 0.04 V, and electrode cleaning time of 20 s. Under these conditions, the proposed method exhibited a linear response for Pb²⁺ in the concentration range of 1.9 × 10⁻⁸ to 1.2 × 10⁻⁷ mol L⁻¹, with a detection limit (LOD) of 5.6 × 10⁻⁹ mol L⁻¹. For Cd²⁺, a linear range of 7.7 × 10⁻⁸ to 2.1 × 10⁻⁷ mol L⁻¹ was obtained with an LOD of 2.3 × 10⁻⁸ mol L⁻¹. The proposed method demonstrated good sensitivity, selectivity, and repeatability, and was successfully applied to the simultaneous determination of Pb²⁺ and Cd²⁺ in food samples, including coffee powder, Thai Nguyen tea, fish, and chicken.