A membrane with ion fluxes responsive to temperature, pH and voltage
Cell membranes of biological cells embedded with nuclear pore complexes (NPCs) are capable of controlling the flow of ions, e.g. Na+, K+ and Ca2+ by responding to stimuli, e.g. pH and voltage. From the inspiration of NPCs, researchers have been endeavoring to develop nanogates to achieve the control of ion transport, but the developed nanogates only have a low selectivity, the factor of change (FC) in ion fluxes due to ON/OFF switching. To our knowledge, nanogates with high responsiveness to temperature changes have not been reported. As such membranes etched with nanopores having a high selectivity (FC) and the reversible gating of temperature, pH and voltage were to be developed in the work. The nanogates were modified with DNA strands, whose linkers, the six nucleobases at 3' ends, are complementary. According to the experimental results, at mildly acidic pH values, e.g. pH 5.3, the prepared nanogate is in an open state, while at neutral pH values, e.g. pH 7.9, it is shut off. The change in ion fluxes is up to a factor of 90, which is remarkably high compared to other nanogates reported. It is observed experimentally that promoting the number of the complementary nucleobases at the 3' ends of the strands would improve nanogate performance significantly, while varying the other nucleobases exerts little effects. Hence the formation of nucleobase pairs among the complementary nucleobases at the 3' ends of the strands leads to the binding of various strands, self-assembly of a strand web and blockage of ion transport. When the temperature is increased, due to the promotion of the thermal motion of DNA strands, the nucleobase pairs and the strand web will not be generated and the nanogate will remain open even at pH 7.9. Hence the nanogate developed is capable of responding to temperature changes. Further experiments were performed to investigate the influence of the NaCl concentrations and small opening diameters exerted on nanogate performance.