Abstract
Biomedical application of the fixation of a photosensitive reagent, tetrabrominated rhodamine (TBR), onto biological tissues model such as collagen gels was studied as a model for photolabeling tissues with medical reagents. Irradiation with an Ar ion laser caused photo-induced debromination and subsequent covalent linkage of TBR to collgen as a tissue model. In this paper, the quantum efficiency of laser induced photolabeling and how dimethylsulfoxide (DMSO) might enhance the efficiency of photolabeling are investigated. Video fluorescence assayed washed gels to measure the unbleached TBR affixed to a gel. A typical experiment used 20 μM TBR, a 4.5% collagen gel, and 1.7 W/cm2 at 488 nm. Prolonged exposure caused 27% of the initial TBR to photolabel the collagen but the peak amount of unbleached affixed TBR occurred at 110s after 187 J/cm2, and equaled 11% of the initial TBR. The quantum efficiency of photolabeling under these conditions was 2.3e-6±1.2e-6 (n=4 trials.) The inclusion of 25% DMSO in the gel increased the photolabeling efficiency 43% to 3.3e-6±1.5e-6 (n=4). A second experiment varied DIVISO levels in the gel but maintained a constant laser exposure of 100 J/cm2. DMSO (10%) doubled the amount of affixed unbleached TBR, and 25% DMSO achieved a maximum 2.4-fold enhancement of photoolabeling. The results showed that laser induced photolabeling can be considered as a convenient method to determine the distribution of light in and on the biological tissue.
