Dynamics of nanoparticles in an Optical Trap studied by Fluorescence Correlation Spectroscopy

This paper reports the results of an experiment that combined fluorescence correlation spectroscopy (FCS) and optical trapping to study the dynamic behavior of nanoparticles in a potential well. Using FCS, we were able to measure the enhanced nanoparticle concentration as a function of optical trapping intensity. Quantitative analysis of this increased density using a balance of inward radiation and outward osmotic pressures permitted the determination of the trapping energy per individual nanoparticle. The values for the trapping energy agreed with those found from a diffusion analysis of the optical trapping-elongated residence times of particles in the focal region. With these self-consistently determined trapping energies, we were able to rescale the trapping power into radiation pressure and calculate the osmotic compressibilities for different sized nanoparticle systems.