Following nanoparticles in complex turbid media
Diffusing wave spectroscopy (DWS) was used to determine the size and volume fraction of nanoparticles (NP) within a foam taken as an example of a turbid media. The presence of two types of scatterers – dispersed NPs and liquid/gas interfaces – leads to two-fold dynamics in the system. Two characteristic decays of the temporal autocorrelation function are observed, their position and amplitude are dependent on particle concentration and foam age. Since only those NPs which are performing Brownian motion decorrelate the signal, one can follow the dynamics of particles' trapping into the foam matrix during the evolution of the system. This technique is a direct and noninvasive way to detect NPs in turbid media. The detection limit strongly depends on the NP nature and an algorithm for its estimation is provided.