Development of sensitive impedimetric urea biosensor using DC sputtered Nano-ZnO on TiO2 thin film as a novel hierarchical nanostructure transducer

Abstract

3D hierarchical Nano-ZnO/TiO2 on conductive fluorinated-tin oxide (FTO) layer was fabricated by reactive direct current (DC) magnetron sputtering of ZnO, at the optimized instrumental deposition conditions, on a pre-covered TiO2 surface with Polyvinyl Alcohol (PVA) as an omissible polymer in a pattern of parallel strips (Nano-ZnO/PVA/TiO2/FTO) following by PVA omission via annealing process, which resulted in an efficient porous media for urease (Urs) enzyme immobilization (Urs/Nano-ZnO/TiO2/FTO) designed for urea biosensing. The criteria for TiO2 selection as substrate was based on: (i) its ability to promote electron transfer between ZnO to FTO substrate, (ii) affording high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents at the biological media, and (iii) enhancement of urea biosensing by the formation of heterojunctions with ZnO. Characterization of the surface morphology of 3D hierarchical Nano-ZnO/TiO2 film by field emission-scanning electron microscopy (FE-SEM) exhibits cavities of nanoporous ZnO film as an effective biosensing area for Urs enzyme immobilization. Step by step monitoring of Urs/Nano-ZnO/TiO2/FTO biosensor fabrication was performed using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fabricated Urs/Nano-ZnO/TiO2/FTO biosensor was used for urea determination using impedimetric assessment. The impedimetric results show high sensitivity for urea detection within 5–205mgdl−1 and limit of detection as 2mgdl−1. A fast response of fabricated biosensor can usually allow a real-time analysis.