Synthesis of WO₃ nanoparticles for biosensing applications

Direct electron transfer with redox proteins, in third generation biosensors, is already proved to be favored on electrodes modified with nanoparticles. In this work, different crystallographic and morphologic structures of tungsten oxide (WO₃) nanoparticles are modified by hydrothermal synthesis at 180°C. The electrochemical properties of WO₃ nanoparticles deposit on ITO electrodes are investigated and the analytical performance of the nitrite biosensor is presented as proof of concept. Despite the inherent features of each nanostructure, the heterogeneous electron transfer with the WO₃ nanoparticles modified electrodes is thoroughly improved and, very importantly, the cytochrome c nitrite reductase (ccNiR) enzyme is able to keep its biological function. When compared with bare commercial ITO electrodes, the exchange rate constant of WO₃/ITO electrodes with cytochrome c increased one order of magnitude, while the analytical parameters of the ccNiR/WO₃/ITO electrodes response to nitrite (the Michaelis-Menten constant is 47 μM and sensitivity of 2143 mA M^-1 cm^-2) are comparable to those reported for carbon based electrodes. Therefore, these metal oxide nanoparticles are good alternative materials for electrochemical applications, such as non-mediated biosensors.