Exploring dynamic light scattering microscopy (MicroDLS): a study of key parameters

Abstract

Dynamic light scattering (DLS) is a technique used to characterize the size of nanometer and sub-micrometer particles in colloidal suspensions. Its non-destructive nature and simple usage make DLS widely applied in fundamental research, research and development (R&D), and quality control processes. While it is not uncommon to encounter the need to measure highly concentrated samples, the applicability of DLS is normally constrained by multiple sample and setupdependent factors. MicroDLS, an optical microscope-based DLS design, has emerged as an effective alternative to measure highly concentrated or heterogeneous samples. Based on microDLS as a platform, we have been developing a method to improve the time resolution of measurements to further apply DLS to time-evolving systems. Herein, we performed various explorations of parameters to test the practical limit of applications by microDLS. Our setup is built based on a confocal optical microscope, a 532nm CW laser, a time-correlated single photon counting system, and a custom post-processing data analysis methodology. We explored the effects of the type of microscope objective and sample concentration on the measurement quality. The measurement of 60nm and 220nm polystyrene particles in suspension at different concentrations, showed the existence of an optimum working concentration range. Finally, the contrast between microscope objectives (20x NA0.4 and 4x NA0.1 air) revealed the specific technical challenges and limitations for each case.