A carbon nanotube-based coulter nanoparticle counter.

This Account reports on the properties and applications of carbon nanotube-based Coulter counters (CNCCs). CNCCs provide a means for determining the diameter and electrophoretic mobility (or electrokinetic surface charge) of individual nanoparticles dispersed in aqueous solutions, as well as the nanoparticle concentration. Such measurements do not require CNCC calibration or sample labeling. Because CNCCs measure the characteristics of individual particles, they provide the true average and polydispersity distribution of nanoparticle properties. CNCCs can differentiate between individual nanoparticles based on their surface charge and size, and CNCCs can be used to determine the apparent surface pK(a) of polymeric nanoparticles. Nanoparticle characterization by CNCC, electron microscopy, conductometric titration, and light scattering are compared.