Scanning gel electrochemical microscopy (SGECM): Elaboration and cross-linking of chitosan-based gel probes

Scanning gel electrochemical microscopy (SGECM) is based on gel probes that are in soft contact with the sample for local electrochemical analysis without needing an additional electrolyte solution. The reproducibility and reliability of the SGECM measurements call for high quality gel probes. In this work, the elaboration of gel probe by electrodeposition of chitosan on microelectrode is detailed, with the key parameters discussed, for the sake of achieving better shape control. For the gel probe fabricated with electrodeposited chitosan on a 25 mu m disk microelectrode, deposition solutions with a pH of ca. 5.5 and microelectrodes with the R-g of 2 similar to 3 are suggested. Cyclic voltammetry of the gel probe in contact with Pt surface shows lower current than that measured in solution by 'classical' scanning electrochemical microscopy, which may be related to the confinement effect. Moreover, an attempt to cross-link the gel by glutaraldehyde after electrodeposition is proposed. After crosslinking for 2 or 4 h, the strength of the chitosan hydrogel increases as supported by force sensing and SGECM approach -retract curves, while the electrochemical behavior of the gel probe is not significantly changed when immersed in 1 mM ferrocenedimethanol solution.