 Solution

In generic resistive-pulse sensing, two electrolyte reservoirs are connected through a small aperture. Electrodes apply a bias and a low-noise current amplifier records the pore current. Passage of a weakly charged insulating particle excludes conducting liquid, usually increasing resistance and giving a transient current decrease at fixed voltage. Pulse amplitude, duration and event rate contain size-, transport- and concentration-dependent information, subject to calibration.

Advantages include label-free single-particle counting, electrical readout and small active volume. Limitations include clogging, electrode/pore noise, finite bandwidth, uncertain particle trajectories and surface-conduction effects; a pulse is not intrinsically chemically specific. Strong particle charge or concentration polarization can complicate, or even reverse, the simple blockade signal. The schematic below uses only generic nonbiological particle transport.