Nanoparticle Tracking Analysis (NTA) technology, which is one of the first commercially available technologies allowing high-resolution particle size distribution on a number-weighted basis and concentration analyses of submicron particles.

NTA technology employs the following steps:

A highly focused laser passes through a liquid dispersion in a specially designed cell.

As the nanoparticles in the dispersion interact with the laser, they are observed as points of light moving under Brownian motion through a microscope.

The rate at which the particles move is a function of their diffusional rate, which is in turn a function of their size as given by the Stokes-Einstein equation.

By tracking the motion of each particle over a specified amount of time, the diffusional rate can be measured and the particle size calculated.

Since the cell is a known volume and the particles present are individually counted, an accurate particle concentration can be calculated simultaneously. 

ASTM E2834-12 describes this innovative technique and provides guidance for industry use.