Mn-doped ZnO thin films as a platform for reagentless uric acid biosensor

Abstract

In this study, sol gel technique is used to fabricate manganese (Mn) doped ZnO thin films and further utilize them as a platform for uric acid biosensors. The objective was to introduce manganese into the ZnO matrix to enhance its redox properties, capitalizing on the multivalent nature of manganese. The Mn-doped thin films of concentrations varying from 3%,5%,7% and 10% were prepared and further characterized using UV-vis spectroscopy, X-ray diffraction (XRD) spectroscopy, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and cyclic voltammetry (CV) measurements. The ZnO thin films with 7% doping of Mn exhibited improved redox behaviour, as evident by the distinct redox peaks. In order to immobilise the uricase enzyme, the 7% Mn doped composition was used, creating a highly sensitive and focused uric acid detection platform. The fabricated biosensor exhibits excellent performance in terms of sensitivity (40 µAmM -1 cm -2 ), selectivity with less than 5% deviation found in presence of other known markers present in human sera, and shelf life more than 12 weeks, enabling precise and sensitive uric acid detection. This study brings to light an alternate approach in developing point of care biosensors using transition metal doped ZnO thin films. This study introduces an innovative approach by incorporating manganese (Mn) into the ZnO thin film matrix to develop a redox-active platform for uric acid biosensing. Traditionally, ZnO-based biosensors have a limitation due to lack of inherent redox properties, generally requiring external redox agents that can limit sensor integration and performance. By embedding Mn directly within the ZnO matrix, we've effectively introduced redox capabilities within the sensor itself, eliminating the need for these external agents. Through systematic optimization, we found that 7% Mn doping yields the best results, enhancing the material's electron transfer and creating a highly stable platform for uricase enzyme binding. The resulting biosensor demonstrated high sensitivity (40 µAmM -1 cm -2 ), excellent enzymatic affinity (K m =0.18 mM), strong selectivity, and long-term stability, with a shelf life of over 12 weeks. These results demonstrate the sensor's potential for use in the development of dependable, portable diagnostic instruments for the detection of uric acid, providing a promising strategy for point-of-care medical applications and addressing associated health risks. Schematic of the reaction occurring at the bioelectrode

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