Thermal characteristics of temperature-controlled electrochemical microdevices

The development of novel, miniaturized sensing systems is driven by the demand for better and faster chemical measurements with lower power consumption and smaller sample sizes. Emerging miniature sensors, or microsensors, also offer rapid thermal and diffusive transport characteristics. For instance, temperature changes, during both heating and cooling, can be achieved on micrometer-scale surfaces much more rapidly than on bulk, macro-scale surfaces. While these rapid thermal characteristics have been most successfully exploited to date in gas-phase sensing devices, the prospect of developing analogous microfabricated, temperature-controlled microsensors for use in aqueous, or solution-phase, environments has been less explored. In this work, electrodes with underlying microheaters were designed and fabricated, and thermal characterization was performed using temperature imaging, transient temperature measurements, and theoretical modeling to determine temperature distributions and thermal response times in both gas- and solution-phase environments. These results will guide the development of solution-phase electrochemical sensors. Temperature-controlled electrochemical characterization was performed using cyclic voltammetry of a model analyte, hexaamineruthenium(III) chloride, to demonstrate the use of the multilayer, microfabricated devices, which consisted of a gold disk electrode and an underlying microheater. Electrochemical signals were enhanced by up to a factor of three at elevated temperatures (up to 81 degrees C) compared to those measured at room temperature (21 degrees C). This improved signal at elevated temperatures was explained by finite element method calculations that accounted for both temperature-dependent diffusion and thermal convection near the heated electrode surface. Published by Elsevier B.V.