Impedance Spectroscopy Study of Glucose Oxidase Functionalized ZnO Nanowires for Electrochemical Glucose Detection

GALLAY, PABLO; TIRADO, MONICA; COMEDI, DAVID

Cancún

Simposio; 21th International Symposium on Metastable, Amorphous and Nanostructured Materials: ISMANAM 2014; 2014

ISMANAM

The quest for glucose biosensors with enhanced sensitivity and selectivity has led researchers to integrate nanomaterials into various functionalized electrodes working in an electrochemistry environment. For glucose detection, glucose oxidase (GOx) enzymatic biosensors have been used extensively, where the transduction method has involved mainly voltamperometric measurements. Although many cases of success have been reported, there remain many questions regarding biosensor repeatibility and stability, which in turn are related to processes that occur at the GOx/nanomaterial and other biosensor interfaces. These processes are very important in the transduction mechanism, which is a key factor in the determination of the biosensor performance, such as its sensitivity and detection limit. In this work, we study GOx functionalized ZnO nanowires deposited on highly doped Si wafers in an electrochemical environment using impedance spectroscopy in a wide frequency range. NWs were deposited by the vapour transport method and functionalized by drop coating GOx in buffer solution in various concentrations. The functionalized NWs were then covered with Nafion solution to immobilize the GOx on the NWs. The systems were characterized at their various fabrication steps by scanning electron microscopy. Impedance spectroscopy measurements where performed in the 10-107 Hz range on an annular electrochemical cell using a platinum sheet as the counter-electrode to the Nafion/GOx/ZnO NW/Si system. The excitation voltage amplitude was 0.05 V; however impedance responses were also studied at different DC biases imposed on the AC excitation voltage. The cell was filled with buffer solutions containing no and various concentrations of glucose to determine the impedance response to different glucose additions. The results showed clear glucose response for optimized fabrication conditions, within specific bias and excitation voltage windows. These responses were fully characterized as a function of the glucose concentration in buffer solution. The impedance data were analyzed using equivalent circuit models that include the various interfaces that take part in the detection process, giving useful insights towards the successful design of ZnO NW based glucose biosensors.