Triggerable single-component two-electrode voltammetric pH sensors using dyad molecules

We have synthesized two types of methoxyphenol thiols, Fc-MP1 and Fc-MP2 to use them in a voltammetric pH sensor. The methoxyphenol group was oxidatively triggered to o-quinone. Thus formed dyad molecules made possible pH measurements based on the pH-dependence of formal potential difference between quinone (pH indicator) and ferrocene (pH reference) moieties. Precise pH measurements over a wide pH range were possible even in a two-electrode mode without a reference electrode. The large polarization effect found in metal counter electrodes such as Au and Pt was removed by simply forming a mixed monolayer using an inert alkanethiol as a diluent. Fc-MP1 and Fc-MP2 were complementary in that Fc-MP2 covers the pH region that was not accessed by Fc-MP1 because of the potential overlap between the Fc+/Fc and Q/H2Q redox processes. The estimated errors were in the range of 0.03 to 0.06 pH units from the analysis of varience.

► We synthesized two complementary dyad molecules that are oxidatively triggered. ► Dyad molecules were used as voltammetric pH sensing components in a two-electrode mode without a reference electrode. ► Polarization effect was eliminated by forming mixed monolayers of dyad molecules and inert alkanethiols. ► Wide pH range could be covered by altering the molecular structure. ► Errors in pH were in the range of 0.03 to 0.06 pH units when operated in a two-electrode mode.