Incorporating Amphoteric Groups in Ion Track-etched Single Conical Nanochannels

Here, we report a facile and straight-forward approach to incorporate amphoteric groups inside the single conical nanochannels. This was realized by direct chemical modification of the surface carboxyl groups with L-lysine chains whose positive and negative charges are very sensitive to the external pH. The chemically functionalised channels were characterized both theoretically and experimentally. The single nanochannel constitutes a universal nanofluidic diode in the sense that the amphoteric chains attached at its surface allow for a broad set of rectification properties. Briefly, the selective functionalization of lysine with surface carboxyl groups was accomplished by blocking the amino group and carboxyl group bonded to the α-carbon with Cu 2+ ion to form a copper-chelate complex. This process leaves an unprotected ε-amino group which was covalently attached with the carboxyl group created during track-etching via EDC/PFP coupling chemistry. 5