Imaging through scattering media with use of photorefractive polymers

Abstract

In the treatment of cancer and macular degeneration with photodynamic therapy (PDT), a class of photosensitizing compounds has been developed by a number of drug companies that are either selectively retained in or are preferentially produced by tumor cells. These dyelike molecules, when exposed to laser light in the visible or UV region, are excited to the triplet state where they have the capacity to promote molecular oxygen to its first excited singlet (IO2). This species is believed to be cytotoxic and causes local necrosis of the tumor cells. However, one particular drawback of the technique is the limit in penetration depth inherent in using visible light as an activation mechanism. Furthermore, treatment of internal cancer sites is necessarily invasive, requiring the use of fiber-optic catheters, endoscopes, or similar instruments. Another activation pathway for this procedure is suggested by results obtained by applying ultrasound to peroxyoxalate chemiluminescent systems (PO CL). In these systems, oxalic acid derivatives react with hydrogen peroxide in the presence of a fluorophore to produce a bright emission characteristic of the fluorescer. This reaction proceeds via an energetic key intermediate, which is proposed to be 1,2-dioxetanedione. In a recent set of experiments, we have observed that when the ester bis(2,4dinitrophenyl) oxalate (DNPO) and the fluorescer rubrene in dimethyl phthalate (DMP) are sonicated with an ultrasonic bath, light is produced at appreciable levels without the addition of hydrogen peroxide. The greatest intensity is observed at the antinodes of the standing waves produced by the sonication bath (Fig. 1). Additionally, the threshold behavior of the CL intensity versus ultrasound power (Fig. 2) suggests that the reactive species