Light-addressable electrochemical sensing (LAES) is a photoelectrochemical sensing technique that uses light to activate a faradaic electrochemical reaction at the surface of a semiconducting photoelectrode. Using LAES it is possible to confine an electrochemical reaction to a microscopic portion of a macroelectrode using focused illumination, which was only previously possible using complex photolithography or scanning electrochemical probe measurements. The advantages to using light to spatially confine an electrochemical reaction on a surface are: faster “switching” times between locations compared to scanning probes; no requirement for pre-patterned electrode surfaces; temporal control of the electrochemical signal; and the ability to have a single electrical connection behave as a sensor array. In spite of these advantages, using LAE sensors have been relatively underutilized. LAE sensors use semiconductors as the light-absorbing electrode material, and as a result understanding and controlling the electrochemical response of these sensors is considerably more challenging than with metallic electrochemical sensors. These challenges are due to the nature of the band structure of the semiconductor, the interfaces between the semiconductor/electrolyte, and the nature of charge transfer across these interfaces. Moreover, when silicon is used as the electrode material, steps must be taken to protect the sensor from corrosion in aqueous electrolytes.

Here we present recent results from our group showcasing semiconductor/metal junctions (also called Schottky junctions) as LAE sensors. In our initial study, we showed that Schottky junctions formed between nSi and Au nanoparticles were excellent candidates for LAE sensors. These junctions can be prepared with a simple benchtop electrodeposition procedure and demonstrate excellent electrochemical properties with near-reversible cyclic voltammetry observed with a number of outer-sphere redox couples. We apply these sensors to the detection of sub-µM concentrations of neurotransmitters and other biologically relevant species (e.g., H₂O₂). We then explore how the semiconductor/metal interface influences the electrochemical properties of the sensors by using Pt and Ni NPs, and carbon nanotubes to alter the photovoltage. Finally, we will show how alternative voltammetric waveforms can be used to provide richer electrochemical information about the interface and increase sensitivity of the sensors.