Gradient Triple-Layered ZnS/ZnO/Ta2O5–SiO2 Core–Shell Nanoparticles for Enzyme-Based Electrochemical Detection of Cancer Biomarkers

We report a methodology to fabricate unique three-layered ZnS/ZnO/Ta2O5 (core)–SiO2 (shell) nanoparticles (CSNPs) with varying compositions of ZnS, ZnO, Ta2O5, and SiO2 in their layers (i.e., gradient structures). An electrochemical approach with better specificity and detection limit for non-neurally secreted cancer biomarker, acetylcholine (ACh), by modifying the glassy carbon electrode surface with enzyme tagged ZnS/ZnO/Ta2O5–SiO2 CSNPs is reported. The size, composition, porosity, and morphology of CSNPs were characterized by using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction technique, and Fourier-transform infrared spectroscopy. A detailed discussion on the mechanism of core–shell formation and the role of ZnCl2 in the core–shell formation is reported. We also demonstrate that the detection limit of ACh could be significantly improved by controlling the thickness of outermost shell layer. Electrochemical investigations performed using differential pulse voltammetry and cyclic voltammetry techniques displayed that the oxidation current of ACh was higher for CSNPs synthesized at 0.15 wt % of ZnCl2 concentration. The limit of detection of ACh was found to be 11.6 nM for CSNPs prepared at 0.15 wt % ZnCl2 concentration. Thus, the CSNPs-based electrochemical sensor platform has high potential for developing a simple, cost-effective biosensor for early detection of cancer biomarker at nanomolar concentration.