In situ observation of molecular diffusion in solid supports using two-photon fluorescence microscopy.

We demonstrate that two-photon fluorescence microscopy is a useful tool for monitoring the diffusion of molecules through polymeric solid supports. As a proof of principle, TentaGel beads were bound to a cover slip, and diffusion of Rhodamine 6G through single beads was observed in real time. Diffusion experiments performed in 40 different beads indicate that there is a considerable degree of heterogeneity in diffusion rates from bead to bead.