Photon correlation spectroscopy for analysis of low concentration submicrometer samples

Abstract

Photon Correlation Spectroscopy is a technique to rapidly measure particle size in the submicrometer region. The use of PCS is, however, limited by concentration. The upper limit is due to multiple scattering of the incident light, the lower limit is determined by the fact that fluctuations of the number of particles in the measuring zone have a significant influence on the apparent diffusion coefficient. In this article a new signal processing method is described which differentiates this influence. With this system the lower limit is no longer limited to about 100 particles in the measuring volume corresponding to a concentration of 10⁹ particles/cm³. The limitation is now the intensity of the scattered light which becomes too weak at a concentration of about 50 particles/cm³. As a consequence of this work, a revision to the basic theory of PCS may be necessary. Moreover, the new processing method enables also the measurement of particle concentration in the sample.