Ion Transport in Nanochannels

Two kinds of nanochannels have been fabricated and ion transport in these nanochannels has been measured. Silica nanotube arrays have been fabricated from Si nanowire templates. The silica nanotubes can be more than 20 μm long with an inner diameter from 10 to 200 nm. A nanofluidic device based on individual silica nanotubes has been fabricated by placing the nanotube on a glass substrate and patterning with respect to individual nanotubes. A similar nanofluidic device with SiNx as the channel wall material has also been fabricated. The cross-section of the SiNx nanochannel is 40 nm high and 1 μm wide, while the channel length extends up to more than 24 μm. Ion transport though these nanochannels has been studied with different concentration KCl solutions to investigate the effects of electric double layer thickness on ion transport. Results show that for high concentration solutions, the measured current fit the theoretical prediction based on the bulk concentration. However, for low concentration solutions, the measured current was larger than that calculated with the bulk concentration, indicating that for low concentration solutions, the ion concentration within the channel was decided not only by the bulk solutions, but also by the surface charge density.