Light Addressable Electroanalysis with Semiconductor/Metal Junctions

Abstract

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 we can confine an electrochemical reaction to a microscopic portion of a macroelectrode using focused illumination, enabling photoelectrochemical imaging of biological processes. 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 electrodes. 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 as LAE sensors. We show that Schottky junctions formed between nSi and Au, Pt, or Ni nanoparticles are 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 will also show how alternative voltammetric waveforms can be used to provide richer electrochemical information about the interface and increase sensitivity of the sensors.