pH-dependent ionic-current-rectification in nanopipettes modified with glutaraldehyde cross-linked protein membranes

In this study, we investigated for the first time the influence of an artificial membrane on the ionic current rectification of nanopipettes at various pH levels. The nanopipettes were fabricated and then modified with bovine serum albumin-glutaraldehyde (BSA-GA) artificial membranes. We determined the degree of ionic current rectification of these nanopipettes and compared them with those of bare nanopipettes. In contrast to the bare nanopipettes, the BSA-GA-modified nanopipettes demonstrated pH-dependent ionic current rectification. We also examined the tunability of the degree of rectification using streptavidin (STV) whose isoelectric point differs from that of BSA. The results showed that the ionic current rectification of nanopipettes can be tuned as the addition of STV into the BSA-GA artificial membrane increases the degree of rectification. Using the proposed approach, nanoscale spearhead pH sensors could be fabricated for highly localized extracellular or intracellular pH measurement. Moreover, it is possible to realize the applications of nano-sized channels in relatively larger channels using the present method.