Dynamic Raman Scattering: Molecular-Selective Correlation Spectroscopy for Diffusion Dynamics in Complex Systems

Diffusion dynamics of polymers and colloidal dispersions at high concentrations have been widely studied using dynamic light scattering (DLS), a correlation spectroscopic method based on Rayleigh scattering. However, DLS has not been applied to complex systems such as biological cells because of its lack of molecular selectivity. Here, we propose dynamic Raman scattering (DRS), a novel molecular-selective correlation spectroscopic technique based on Raman scattering. We theoretically demonstrate that molecular-selective diffusion dynamics can be monitored by measuring the intensity fluctuation of coherent anti-Stokes Raman scattering in a phase-mismatching condition. We then experimentally prove the molecular selectivity of the DRS by extracting the polystyrene diffusion dynamics in a mixture of polystyrene and silica nanoparticles. We believe that DRS will be applicable for monitoring diffusion dynamics in complex dispersions without any pretreatment.