Demonstration of Coulter counting through a cylindrical solid state nanopore

The technique known as a Coulter counting, or resistive-pulse sensing, can be used to measure the size of a nanoscale analyte as it passes through a fluidic constriction separating two reservoirs. We have developed a fabrication procedure capable of reproducibly manufacturing cylindrical nanopores with diameters as small as 20 nm using a silicon-on-insulator substrate and electron beam lithography. The ionic conductance of these nanopores was measured across six orders of magnitude in electrolyte concentration. Polystyrene nanoparticles were then passed through the cylindrical pores while monitoring the current that flowed due to a constant bias voltage. Current pulses due to the passage of individual nanoparticles of various dimensions through a nanopore were observed and compared to theory.