As the chemical environment grows more complex in research and industrial settings, there is an increasing demand for robust and flexible sensors for volatile chemicals. Nanomaterials are a promising new frontier of investigation to tackle these challenges. While the praise of nanosensors often focuses on their high surface area, the ability to exploit nanoscale phenomena for transduction opens up exciting possibilities. The drawback of many nanoscale sensing platforms is challenging fabrication. In this work, we utilize a simple but highly controllable electrochemical method to form nanoporous gold, as well as its Pt alloy derivatives with even finer pore sizes. Rather than applying nanoporous gold to a conventional aqueous electrochemical sensor, we leveraged unique nanoscale phenomena to apply nanoporous gold as the first reported multi-variate gas sensor.

Electronic conduction in nanoporous networks is fundamentally different from bulk metallic conduction. While conduction in bulk systems is limited by phonon scattering, electrons in nanoporous gold scatter off surfaces before they encounter a phonon. This behavior is strongly modulated by chemicals adsorbed to the surface. Since the quantity adsorbed on the surface depends on the equilibrium with the gas concentration, one can use changes in resistance to sense the gas concentration. We have demonstrated this detection principle for several model volatile chemicals (water, acetone, ethanol).

By monitoring both the in phase and out of phase electrical response, we also observed changes in the capacitive behavior. These capacitive changes were driven by pore filling. Condensed liquid within the pores allows for the formation of an electric double layer. This condensation occurs far below the typical saturation pressure due to the confined curvature of nanopores. By combining such data with changes in electrical resistance, we demonstrate robust and selective gas sensing.

In this work we demonstrate that a single multi-variate nanoporous gold gas sensor can detect multiple compounds (water, acetone, ethanol). We also measure sensor characteristics: sensitivity, delay, and hysteresis. These results show the potential for the application of nanoporous gold as a versatile and selective volatile chemical sensor.