A practical guide to working with nanopipettes

Abstract

Nanopipettes are a powerful solid-state nanopore platform with applications including single-particle characterization, surface mapping, and high-sensitivity analytical measurement in both bulk solutions and in localized spaces. While the capabilities of the platform have been aptly demonstrated, practical challenges associated with the nanopipette fabrication, filling, and surface modification remain. Progress and advancement to a high device readiness level are also hindered by low reproducibility and low throughput, as well as the consequent entry barrier for new research groups. This perspective provides the accumulated practical experience of our research group, forming a practical guide to overcoming the technical hurdles that are rarely discussed within the primary literature. We outline fabrication protocols, namely the importance of environmental conditions and instrument maintenance for enhanced reproducibility, as well as the desirable nanopipette geometries to facilitate ease of filling and surface modification. Filling procedures are discussed, and the interplay of surface wetting, capillary forces, and surface chemistry is used to understand how filling issues might be mitigated. Silanization of nanopipettes as a route for surface modification of the nanopipette interior is also discussed, with a particular focus on vapor-phase silanization. General design principles for surface grafting reactions are offered to maximize throughput and reproducibility. Throughout the perspective, the interconnected nature of the fabricated geometry, filling, and the modification pathways are highlighted, and this perspective is meant to facilitate the design of a holistic workflow where each stage is considered in tandem, facilitating higher throughput and more reproducible nanopipette research.