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licentiate seminar, Stina Guldbrand, 13/12

News: Dec 02, 2010

Licentiate thesis presentation

Stina Guldbrand

Department of Physics

Two-photon Fluorescence Correlation Spectroscopy for Quantitative Analysis of Xenobiotics in Human Skin

Location: Lecture hall FL63, F-building

Time: Monday 13th December at 10.00

Opponent: Christian Brackman


Abstract

The method two-photon fluorescence correlation spectroscopy (TPFCS) has been used in combination with measurements of the point spread function (PSF) to measure the diffusion coefficient of xenobiotics in excised human skin. TPFCS is a non-invasive method which enables deep penetration in biological tissues. In this study, measurements have been performed at depths from the surface down to 40 um. The PSF was measured using subresolution beads embedded in the skin samples and the FWHM of the emitted intensity was measured. Average values of the PSF in skin was found to be 0.41 um in the lateral direction and 1.2 um in the axial direction. Those values are similar to the measured PSF in water. The PSF in skin was found top be independent of the skin depth. The fluorophores Sulforhodamine B (SRB), Rhodamine B (RB) and Rhodamine B isothiocyanate (RBITC) were used for the TPFCS measurements. The diffusion coefficient of SRB in skin was found to be two orders of magnitude slower that the diffusion of SRB in solution.

The diffusion of the reactive molecule RBITC was compared to its unreactive analogue RB. The diffusion coefficient for RBITC was twice as large than for RB. The hydrodynamic radii for RB and RBITC were calculated using Stokes- Einstein equation and were found to be 0.61 um for RB and 1.0 um for RBITC. This could correspond to a molecular weight of 500 for RB and 12000 for RBITC. The weight for RBITC corresponds to that of a large protein which implies that the diffusion measured for RBITC is indeed the diffusion for the entire RBITC protein complex.

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