Role of the real first interface in regulating ionic signal of nanochannels.

Mass transport through nanochannels involves interactions across six distinct regions, including the "real first interface" (RFI), a region formed by functional elements extending into the bulk solution and their surrounding bulk solution. While previous studies have revealed the roles of the bulk solution, outer surface, and inner wall, the contribution of RFI remains unclear due to its susceptibility to interference from neighboring regions, which makes its individual role difficult to isolate. Herein, we show that a diblock DNA probe can be used to independently investigate the RFI by keeping the properties of the other five regions constant. Our results demonstrate that the RFI's role in regulating ionic current in our system is mainly determined by charge effects. These findings highlight the distinct and previously underappreciated role of the RFI in nanochannel transport and suggest that resolving its function may provide the final piece in understanding ion transport mechanisms in confined systems.