Dopamine levels determined in synthetic urine using an electrochemical tyrosinase biosensor based on ZnO@Au core–shell

This work presents a biosensor based on core–shell nanostructure formed by zinc oxide (ZnO) nanoparticles coated with gold (Au). The core–shell nanostructure served as a support for the immobilisation of tyrosinase on screen-printed carbon electrodes to measure dopamine using differential pulse voltammetry. While ZnO is a semiconductor with good electrical conductivity, Au offers high stability and biocompatibility, which is beneficial for maintaining enzyme activity. Atomic force microscopy (ATM), ultraviolet (UV) and infrared (IR) spectroscopy measurements confirmed that the core–shell was successfully formed. The biosensor comprising of ZnO@Au core–shell nanostructures with immobilised tyrosinase allowed the detection of dopamine in real samples with remarkable selectivity and accuracy with a relative error of 3.8%. The limit of detection and dynamic range of the biosensor for dopamine in real samples were 86 nmol L⁻¹ and 0.1 to 500 μmol L⁻¹, respectively. Thus, the results indicate that the proposed miniaturized biosensor device is promising for the monitoring of dopamine in real samples and can be used for disease diagnosis and prognosis. Furthermore, the reported electrochemical biosensor is of low-cost when compared to conventional techniques.