Scanning Gel Electrochemical Microscopy (SGECM): Lateral Physical Resolution by Current and Shear Force Feedback.

Scanning gel electrochemical microscopy (SGECM) is a novel technique measuring local electrochemistry based on a gel probe. The gel probe, which is fabricated by electrodeposition of hydrogel on a microdisk electrode, immobilizes the electrolyte, and constitutes a two-electrode system upon contact with the sample. The contact area determines the lateral physical resolution of the measurement, and considering the soft nature of the gel it is essential to be well analyzed. In this work, the lateral physical resolution of SGECM is quantitatively studied from two aspects: (1) marking single sampling points by locally oxidizing Ag to AgCl and measuring their size; (2) line scan over reference samples with periodic topography and composition. The gel probe is approached to the sample by either current or shear force feedback, and the physical resolution of them is compared. For the optimal gel probe based on 25 μm diameter Pt disk electrode of Rg ≈ 2, the lateral physical resolution of SGECM at contact position is ca. 50 μm for current feedback and ca. 63 μm for shear force feedback. More importantly, the lateral physical resolution of SGECM can be flexibly tuned in the range of 14-78 μm by pulling or pressing the gel probe after touching the sample. In general, current feedback is more sensitive to gel-sample contact than shear force feedback. But the latter is more versatile, which is also applicable to nonconductive samples.