(Invited) Scanning Gel Electrochemical Microscopy: Towards Biological Applications?

Abstract

Scanning electrochemical probe techniques have been developed in the last 30 years for measuring spatially localized electrochemistry at micro and nano scale. Here, we will present a recently developed tool, namely Scanning Gel Electrochemical Microscopy, for imaging the electrochemical reactivity of surfaces and patterning surfaces by local electrodeposition. The concept is based on a gel probe that is in soft contact with the sample, allowing electrochemical measurements to be spatially localized in the contact area with gel as electrolyte.1 The physical resolution, or the pixel size, can thus be tuned by pressing or pulling the probe after touching the sample.2 So far, two types of gel probes have been developed: Type I by electrodeposition of chitosan on micro-disk electrodes,1-3 and Type II by “electrodeposition + pulling” on sharpened metal wires.4 Local chronoamperometry, potentiometry and cyclic voltammetry have been carried out, either for imaging or for patterning (complex-shaped) surfaces.1-4 The gel has an advantage of localizing and immobilizing the electrolyte, which “frees” the sample from solution in scanning electrochemical microscopy (SECM) and reduces the wetting in scanning electrochemical cell microscopy (SECCM) as supported by quartz crystal microbalance (QCM) measurements in our recent work.5 Moreover, the excellent biocompatibility of the chitosan-based gel (which can easily immobilize drugs, proteins or bacteria) and the soft contact make SGECM a promising technique for biological applications. In this presentation, we will discuss about the feasibility of measuring different possible responses when a gel probe is in contact with a bio-entity (bacteria, bio-film, etc.) in-situ in its culture media: (1) Transport of redox species through the bio-entity, either from the gel to the culture media or the opposite way; (2) Production of redox mediators by the bio-entity that would be captured by the gel probe; (3) Physical and chemical response of the bio-entity induced by the gel probe. These possibilities will be examined by electrochemical modelling. The recent development on polyvinylalcohol-based gel probes will also be introduced. The work is partially supported by ANR-NRF project MEACT (ANR-20-CE09-0028).