Silver Nanoneedle Probes Enable Sustained DC Current, Single-Channel Resistive Pulse Nanopore Sensing

Resistive pulse sensing using ion channel proteins (biological nanopores) has been evolving as a single-molecule approach to detect small biomolecules owing to atomically precise pore size reproducibility, high signal-to-noise ratio, and molecular selectivity. The incorporation of biological nanopores in sensing platforms requires a stable lipid membrane that can be formed by a variety of methods such as the painting method and droplet-based techniques. However, these methods are limited by the fragility of the unsupported bilayer or the need for specific microdevices. Electrode-supported bilayers, in which a metal electrode is used as a support structure, have been recently developed using a fine gold nanoneedle. We previously described the utility of the gold nanoneedle-supported ion channel probe to detect small molecules with high spatial resolution; however, it exhibited a channel current decay over time, which affected the binding frequency of the target molecule to the protein pore as well. Here, we introduce a silver nanoneedle probe to support the lipid bilayer formation and ion channel measurements. The silver nanoneedle mitigates the current decay observed on gold electrodes and produces stable DC channel currents. Our findings propose the formation of a AgCl layer creating a nonpolarizable electrode. The new nanoneedle is successfully applied for single-molecule detection of sulfonated β-cyclodextrin (S₇βCD) using αHL as a test bed protein. We believe that this new silver nanoneedle platform has great potential given the relative ease of lipid bilayer formation and stable open channel currents.