Electrochemical biosensing platform based on molecularly imprinted polymer reinforced by ZnO–graphene capped quantum dots for 6-mercaptopurine detection

A new quantum dot consisting of a ZnO core wrapped in a shell of graphene (ZnO@GQD) was synthesized and applied for the construction of an innovative electrochemical sensor for sensitive and selective determination of 6-mercaptopurine (6-MP). The sensor was fabricated based on the pencil graphite electrode (PGE) coated with a sol-gel binder reinforced with polypyrrole (PPy) based molecularly imprinted polymer (MIP), and ZnO@GQD core-shell nanoparticles with a homogeneous environment. The procedure was carried out through a facile one-step electropolymerization stage. The synthesized quantum dots were studied by Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX). Electrochemical characterization of the sensor was performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). To clarify the oxidation mechanism of 6-MP, various voltammetry techniques were used. Electrochemical measurements using differential pulse voltammetry (DPV) method showed a wide linear relationship between 6-MP concentration and peak height within the range 0.01–50.0 μM and 50.0–700.0 μM with a lower detection limit (5.72 nM). The imprinted sensor was highly sensitive and was successful to detect 6-MP in real spiked samples.