Hot-SWV: Square Wave Voltammetry with Hot Microelectrodes

A promising strategy to lowering detection limits in electrochemical analysis is the active modulation of the electrode temperature. Specifically, by tuning the electrode's surface temperature one can enhance detection limits due to improved electrode process kinetics and increased mass transfer rates, all without affecting the bulk solution. Motivated by this argument, here we report the development of a new electroanalytical technique based on electrode-temperature modulation, which we call hot square wave voltammetry (Hot-SWV). The technique utilizes the superposition of conventional SWV, already considered as one of the most sensitive voltammetric techniques, and a high frequency alternating current (ac) waveform to electrically polarize microelectrodes. By applying about 100 MHz ac frequencies (with varying Vrms amplitudes), our method generates an electrothermal fluid flow (ETF) in the electrolyte surrounding the electrode, thereby increasing the sensitivity of the SWV-based detection. We demonstrate this by investigating the oxidation of ferrocyanide and iron(II) ions, as well as the reduction of the coordination compound ruthenium(III) hexamine under various experimental conditions. We validate our experimental results against a theoretical model built using finite element analysis and observe agreement within ≤15% error at temperatures ≤39 °C. Using Hot-SWV, we observe at least one-order-of-magnitude improvement in the limit of detection of ferrocyanide ions relative to conventional, mm-size electrodes at 25 °C. In addition, we anticipate that Hot-SWV will be particularly useful for electroanalytical measurements of ultralow (≤pM) concentrations of analytes in environmental and biomedical applications.