Application of fluorescence correlation spectroscopy for drug delivery to tumor tissue

Quantitative fluorescence microscopy methods can provide valuable insight into drug delivery and pharmacokinetics. We are investigating the use of single photon fluorescence correlation spectroscopy (FCS) to measure particle concentration and mobility in living tissue. In this study we examined whether a relatively large illumination volume could be used to probe the state of macromolecules in free solution and in tissue. The FCS set-up is based upon an upright research microscope, diode laser with 635 nm wavelength, an avalanche photodiode/single photon counting module, and PC based correlation electronics. Diffusion coefficients were e4xtracted from measured autocorrelation functions. We used fluorescent monodisperse beads with diameter 20 and 200 nm to calibrate the excitation volume. Particle diffusion coefficients measured by FCS were compared with conventional light-scattering measurements. We then applied the technique to measure fluorescently labeled liposome distribution in tissue and tissue models. We found that the difference in quantum brightness and diffusion times of liposomes and free dye may be used to detect changes due to liposome interaction with living cancer cells.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.