Entrance effects based Janus-faced nanopore for applications of chemical sensing

Nanopore is an important class of nanofluidic devices, which has growing applications for bio-chemical sensing. The pore size and surface properties were predominant for the ion/mass transport. However, the recent theoretical studies demonstrated the entrance effects can be another key factor. Here we reported experimental approval of this concept by an asymmetric surface coating technique using reactive and stopping liquids, named as a Janus-faced nanopore. Our results showed a clear rectified current of the asymmetric exterior charged surface on a single SiN nanopore, matched well with the theoretical predictions. Finally, we take the recognition of K+ as an example by coating 4-aminobenzo-18-crown-6 on single side of the nanopore, again using the concept of a Janus nanopore. The trapped K+ at exterior surface induced change of current rectification that can be electrically measured. The advantage of using a Janus nanopore is to make sensing functional at the exterior surface of nanopore, avoiding the slow diffusion of molecules in the nanochannels. We believe the Janus nanopore has potential applications for the clinical diagnosis or biosensing in the level of single molecule, besides the fundamental transportation studies.