Detection of Sunlight Exposure with Solar-Sensitive Liposomes that Capture and Release Food Dyes

Abstract

Direct assessment of sunlight exposure can be challenging over extended periods or in multiple remote locations. We optimized liposome formulations that included egg and hydrogenated soy lipids as well as small amounts of a chlorophyll-derived phospholipid (PoP) to confer sunlight reactivity and triggered-release of entrapped dyes. Dye release occurred with PoP-mediated photooxidation of unsaturated phospholipids and could be tuned by varying the unsaturated (egg) to saturated (soy) lipid ratio or by varying the amount of PoP included. Numerous food coloring dyes were entrapped within the liposomes and, when applied onto a polyacrylamide gel, remained intact and immobilized for at least a month in the dark. When exposed to sunlight, the dyes were released and rapidly diffused through the gel, creating a detection system for assessing sunlight exposure by the naked eye based on dye diffusion. Acid Blue 9 and Acid Yellow 23 were particularly effective reporter food dyes in this system. By using liposomes with varying PoP amounts, light-induced dye release could be tuned to coincide with varying amounts of solar exposure. Additionally, exposure-dependent, color-coded release patterns were generated using colloidal mixtures of separately formed liposomes loaded with different dyes. Using customized 3D printed enclosures, a small and readily deployable device was created for visualizing solar-sensitive liposome sunlight reporting. These studies show proof-of-principle that PoP liposomes can serve as simple nonelectric reporters for visually assessing sunlight exposure based on diffusion of entrapped food coloring.