Direct Single-Impact Electrochemistry Using Silver Nanoparticles as a "Digital" Readout for Biosensing Applications

Direct single-impact electrochemistry is a rapidly evolving analytical method based on the collision of redox-active species, such as silver nanoparticles (AgNPs), with a biased microelectrode. The collision results in distinct current spikes due to partial or complete oxidation of a particle. In recent years, this technique has been applied in various biosensing strategies as a "digital" readout technique. It offers the quantification of analytes using discrete signals, as opposed to conventional amplitude-based methods. In this review, we explore the latest advancements in direct single-impact electrochemistry for biosensing applications. In addition, we summarize the key factors influencing the "digital" readout performance and their interrelationships, including particle size and corona, electrode size and potential, electrolyte composition, particle mass transport toward the electrode, and data acquisition. Considering recent experimental developments and theoretical principles, we have identified guidelines that are expected to facilitate and accelerate the development of novel direct impact-based sensing platforms, particularly for point-of-care (POC) applications.