Difference between detection and tracking of nanoparticles

Detecting a nanoparticle means knowing whether it is present or not. This is a point (in time) measurement and yields a binary result. For instance, a flow cytometer registers a signal that crosses a threshold if a particle is in the observation area (see: Effects of swarm of particles in flow cytometers). This can be extended if one looks at the intensity of the signal and tries to extract more information, such as the particle size (or mass).

Tracking, on the other hand, implies connecting several time-point measurements. It means knowing the position of the same particle at different time-stamps. This is what the NTA technique uses (see: nanoparticle tracking analysis). In order for the tracking to be able to provide information on the particles, the time resolution should be higher than the characteristic diffusion or advection¹ time.

References: [@Faez2015Fast, Label-Free Tracking of Single Viruses and Weakly Scattering Nanoparticles in a Nanofluidic Optical Fiber]

See further: limitations of nanoparticle tracking analysis