| Substantial attention is being paid to ion transport and sensing in nanofluidic devices because of the unique transport properties these nanoscale conduits exhibit and their potential analytical applications. Some aspects of microscale transport transfer directly to the nanoscale, but nanofluidic systems can be significantly influenced by phenomena such as double-layer overlap, surface charge, ion-current rectification, diffusion, and entropic forces, which are either insignificant or absent in larger microchannels. Microand nanofabrication techniques are able to create features with a wide range of welldefined geometries and dimensions in synthetic and solid-state substrates. Moreover, these fabrication techniques permit coupling of multiple nano- and microscale elements in series and parallel that can be used to execute a series of functions.;Of the variety of nanofluidic conduits available, we chose to work with cylindrical and conical track-etched nanopores in poly(ethylene terephthalate) membranes. To improve our understanding of ion transport, ion-current rectification is studied by evaluating current--voltage behavior through single nanopores. The effects of nanopore dimensions, buffer ionic strength, and buffer pH on current rectification are systematically examined. Surface charge on the nanopore wall plays an increasingly important role as ionic strength decreases, and the relative contributions of the surface charge and ion concentration in the nanopore to conductivity leads to a maximum in the rectification ratio at a buffer concentration specific to the pore properties. These observations are confirmed by numerical simulations. We also isolated single track etched nanopores between two microchannels. This integration improves mass transport to the nanopore and allows probing of the role of surface charge on phenomena such as ion depletion and sample stacking at the microchannel-nanopore interface.;We also used these nanopore devices to characterize the physical properties of single virus particles and to monitor the assembly of hepatitis B virus (HBV) capsids by resistive-pulse sensing. In our sensing experiments, the T = 3 and T = 4 icosahedral complexes are easily discriminated by the measured difference in their pulse amplitudes, which are proportional to particle size. In addition, these nanopore devices were used as a label-free approach to monitor assembly of single virus capsids in real time and at biologically relevant concentrations, as well as to observe intermediates formed during the assembly process. |
