Integrated ultramicroelectrode-nanopipet probe for concurrent scanning electrochemical microscopy and scanning ion conductance microscopy.

Scanning ion conductance microscopy (SICM) has developed into a powerful tool for imaging a range of biophysical systems. In addition, SICM has been integrated with a range of other techniques, allowing for the simultaneous collection of complementary information including near-field optical and electrophysiological properties. However, SICM imaging remains insensitive to electrochemical properties, which play an important role in both biological and nonbiological systems. In this work, we demonstrate the fabrication and application of a nanopipet probe with an integrated ultramicroelectrode (UME) for concurrent SICM and scanning electrochemical microscopy (SECM). The fabrication process utilizes atomic layer deposition (ALD) of aluminum oxide to conformally insulate a gold-coated nanopipet and focused ion beam (FIB) milling to precisely expose a UME at the pipet tip. Fabricated probes are characterized by both scanning electron microscopy and cyclic voltammetry and exhibit a 100 nm diameter nanopipet tip and a UME with an effective radius of 294 nm. The probes exhibit positive and negative feedback responses on approach to conducting and insulating surfaces, respectively. The suitability of the probes for SECM-SICM imaging is demonstrated by both feedback-mode and substrate generation/tip collection-mode imaging on patterned surfaces. This probe geometry enables successful SECM-SICM imaging on features as small as 180 nm in size.