Monte Carlo Simulation of FCS in a Laser Gradient Field

摘要

Fluorescence Correlation Spectroscopy (FCS) is an attractive technique for probing the molecular inetics in solutions. However, gradient field due to a focused intense laser field may affect the measured results. Since finding an anlaytical solution of the diffusion equation in a gradient field is not easy, we developed a Monte Carlo method to simulate Browning motion of Rayleigh particles in a laser gradient field. Effects corresponding to different parameters were tested in the simulation. Simulated results for zero gradient field agree well with the analytical solution, which has been used in all the conventional FCS measurements. Simulated results with gradient fields indicate changes in the fitted diffusion time and the average number of fluorescent spheres (N) in the effective volume. The simulated results agree qualitatively to the experimental results obtained using fluorescent spheres. Empirical relations from the simulation are discussed.