Soft Surfaces for Fast Characterization and Positioning of Scanning Electrochemical Microscopy Nanoelectrode Tips

The testing of nanoelectrode tips for scanning electrochemical microscopy (SECM) is a slow and cumbersome task that often results in untimely electrode breakage due to crashing against a substrate. Here, we evaluated approach curves of nano- and microelectrodes to soft surfaces using SECM for a rapid and more convenient characterization and positioning protocol. Soft surfaces consisted of either a submerged argon bubble or a thin polydimethylsiloxane (PDMS) layer. While approach curves to Ar bubbles in the presence of a surfactant were promising for the characterization of microelectrode tips, their performance with nanoelectrodes was deficient. In contrast, approach curves to PDMS films allowed the rapid positioning of nanoelectrodes as small as 30 nm radius at speeds up to 5 μm/s without the risk of breakage. The nanoelectrodes were able to approach the polymer films multiple times without affecting their electrochemical performance. Furthermore, using a half-coated substrate with PDMS, nanoelectrodes could be retracted and positioned very close to the bare, hard substrate for characterization with traditional approach curves. We estimate time savings on tip characterization/positioning on the order of 10- to 100-fold. This simple procedure is easily implemented without the requirement of additional devices supplementing existing commercial SECM instruments.