Novel pH sensor based on anthraquinone-ferrocene modified free standing gold nanowire array electrode

A novel electrochemical pH sensor was fabricated through the use of an anthraquinone-ferrocene (AQ-Fc) complex based on a vertically aligned gold nanowire array electrode (AuNAE). The sensing capability was achieved by monitoring the variation in peak potential of the redox active/pH active anthraquinone moiety with respect to the redox active ferrocene moiety. The pH sensor, based on AQ-Fc/AuNAE, was characterised using scanning electron microscopy (SEM) and cyclic voltammetry (CV). The difference in peak potential of the ferrocene and anthraquinone moieties was measured using square wave voltammetry (SWV) and was found to be linear over the range of pH 2-11, with a sensitivity of 1.38 V pH^-1 cm^-2 at 25 °C. The electrode was found to respond both in the presence and absence of oxygen, further expanding the potential applications to include de-oxygenated environments. The sensor showed a potential drift of 1.0-3.3% after three hours and 95% of the signal was retained after one week. Such single molecular complex (AQ-Fc) based pH sensors should provide easy manufacturing and long term stability when incorporated into the sensor designs.