Robust label-free CuxCoyOz electrochemical sensors for hexose detection during fermentation process monitoring

Label free electrochemical sensors of glucose are used whenever long-term operation and stable response are required. For this purpose, various metals and oxides of the first transition series have been proposed as alternative to more expensive noble metal electrochemical sensors. In this work we propose a new formulation consisting of copper-cobalt mixed oxides which, in the form of porous and nanostructured thin films with well controlled Co/Cu ratio, are prepared at room temperature in one step by a modification of the magnetron sputtering oblique angle deposition procedure. Films with various compositions were electrochemically characterized by cyclic voltammetry to determine their amperometric response to glucose as a function of voltage and NaOH electrolyte concentration. This analysis showed that films with a Co/Cu atomic ratio equal 3.4 presented a maximum sensitivity (0.710 A M−1 cm−2), a small limit of detection (0.105 μM) and a resilient behaviour upon cycling operation and long storage periods that clearly overpassed the performance of copper and cobalt single oxides. The CuxCoyO electrocatalysts also presented a good selectivity towards glucose and fructose in the presence of common interference compounds found in biological fluids (e.g., ascorbic acid, acetaminophen and uric acid), sucrose and ethanol, this latter present in many agrofood liquids. The possibilities of this sensor electrocatalyst have been tested for the analysis of a wine synthetic fermentation process. The comparison of the electrochemical results with conventional analytical methods showed a lineal amperometric response with respect hexose contents in a must at different stages of its transformation into wine.