Use of osmotically active agents to alter optical properties of tissue: Influence on the detected fluorescence signal from a subsurface target

In this study, we used a technique that alters the optical properties of tissue to study the effects of tissue scattering on the detected fluorescence from a target placed under the tissue sample. By using hyper-osmotic solutions of glycerol or dimethyl sulfoxide, scattering in tissue samples was reduced substantially. A fluorescent film was placed underneath in vitro and in vivo samples of hamster skin. Excitation of the fluorescent film was achieved through the tissue and the fluorescent signal from the film monitored over time as an osmotically active agent was added to the tissue. The film had an absorption peak at 542 nm and an emission peak at 585 nm. The reduction in tissue scattering caused by the optical clearing agents led to an increase in the detected fluorescent signal (up to double the original signal). The increase was greater for 14 M dimethyl sulfoxide than for 13 M glycerol, and greater for in vivo skin than for in vitro skin. The study serves as a demonstration of the benefits of optical tissue clearing by osmotically active agents to the detected signal in an optical application. Temporary reduction of scattering in tissue will be useful in therapeutic and diagnostic applications that can benefit from an increase in the penetration depth of light.