Abstract: Methods and systems suitable for tracking Brownian motion of particles suspended in a fluid and determining the diffusion coefficient of the particles therefrom in order to characterize the particles, their synthesis, and/or their surface modifications. The methods include providing a sample having particles suspended in a fluid, obtaining and recording at least first and second images of the sample wherein the first image obtained at a first time and the second image subsequently obtained at a second time, determining the average displacement of the particles in an area of the first and second images during a time period between the first time and the second time based on the first and second images, and then determining a diffusion coefficient of the particles in the area of the first and second images based on the average displacement of the particles during the time period.