Square-Wave Voltammetry Enables Measurement of Light-Activated Oxidations and Reductions on n-Type Semiconductor/Metal Junction Light-Addressable Electrochemical Sensors

Abstract

Light-addressable electrochemical (LAE) sensing is a photoelectrochemical technique that enables high-density, individually addressed electrochemical measurements using light to activate an electrochemical reaction at the surface of a semiconducting photoelectrode. However, one major challenge is that only one electrochemical reaction (oxidation or reduction) will be activated by light. Here, we used square-wave voltammetry (SWV) to enable measurement of both types of electrochemical reactions using n-Si/Au NP LAE sensors. We demonstrated this approach for the oxidation of ferrocene methanol and the reduction of ruthenium hexamine and methylene blue. We found that for all molecules, SWV showed dramatic improvements in current under illumination in comparison with dark samples. We also demonstrated that this approach works for both fully illuminated and partially illuminated samples. Altogether, we hope these results open up new applications for LAE sensors, especially those based on semiconductor/metal junctions.

Field-Effect Sensors Combined with the Scanned Light Pulse Technique: From Artificial Olfactory Images to Chemical Imaging Technologies

“…Light-activated electrochemistry has been applied to two-dimensional interrogation ("electrochemical reading") [48,50] as well as electrochemical deposition on the surface ("electrochemical writing") [50]. When combined with an amperometric sensing principle, it can potentially be applied to a device that should be called a light-addressable amperometric sensor (LAAS) [20,21,[52][53][54][55] or a light-addressable electrochemical sensor (LAE sensor) [8,[56][57][58][59].…”

Electrodeposition Parameters Dramatically Influence the Morphology, Stability, and Performance of n‐Si/Pt Light‐Addressable Electrochemical Sensors

“…The supporting electrolyte was used by Allongue et al (and subsequently by us and others) to deposit Au on n-Si. [36,37,48,49] We applied a very cathodic electrodeposition potential (E dep ) of À 1.945 V vs. SCE, which has been shown to improve mono-dispersity in electrodeposited films, possibly due to adsorption and evolution of H 2 during metal deposition. [50] During electrodeposition, we observed large cathodic currents (typically ca.…”

“…LAE sensors were fabricated similar to our previous protocol (depicted schematically in Figure 2a). [36,37] Briefly, n-type silicon was diced into 1.5 cm by 1 cm pieces by scoring the dull side of a single-side polished wafer with a diamond tipped pen and cracking along the score line with a straight edge. Great care was taken to prevent the scratching of the polished side of the wafer.…”

“…[36] We subsequently showed that both oxidation and reduction reactions could be studied with n-Si/Au LAE sensors by probing them with square wave voltammetry. [37] Gooding and co-workers also used Au NPs in contact with Si, but attached them to the surface using a self-assembled monolayer. [38] Loget, Sojic and coworkers employed Si/SiOx/metal (e.g., Ni, Pt, Ru, Ir) junctions to perform light addressable ECL.…”

Characterizing and understanding the photovoltage in n-Si/Au light-addressable electrochemical sensors

“…While other methods exist for fabricating LAE sensors, we are particularly interested in LAE sensors based on semiconductor/metal (SM) or semiconductor/insulator/metal (MIS) junctions. 3–10 SM- and MIS-LAE sensors use a semiconductor to absorb light, separate electron/hole pairs (e − /h + ), and transport e − /h + to the appropriate interfaces, while the metal serves as the interface for the electrochemical reaction and depletes the semiconductor of minority carriers. SM and MIS junctions are also widely used for energy storage applications because sunlight can be used to drive the oxidation and reduction of water to O 2 and H 2 , respectively.…”