Green-light responsive fluorescein-based photoremovable protecting group: nanoparticle formulation for controlled release of bioactive molecules with real-time-monitoring ability†

Abstract

Dye-based photoremovable protecting groups (PRPGs) are explored for biological applications because they release bioactive molecules by absorbing light at higher wavelengths, and their self-fluorescent properties make them suitable for cellular imaging and image-guided photorelease inside the cells. Henceforth, we modified fluorescein dye to a cinnamyl-based PRPG for the release of alcohols to overcome the limitations of multiple photoproduct formation. The carboxylic acid group at C1 and the phenolic-OH group at the C6 positions in the fluorescein PRPG resulted in interesting pH-sensitive photophysical properties due to their existence in different forms (lactone, quinoid, monoanionic, dianionic) at different pHs, which is well supported by theoretical studies. Caged esters (3a–e) of fluorescein-based PRPG released the corresponding alcohols with good chemical yields and moderate photouncaging quantum yields upon exposure to green light. To enhance the biological utility, our developed fluorescein PRPG was formulated as nanoparticles (Nano-3d) having better cell penetration and accumulation. Interestingly, the fluorescein-based PRPG exhibited a change in fluorescence after photorelease ensuring its real-time monitoring ability in biological media. Furthermore, green light (525 ± 5 nm) exposure of our prepared nanoparticles (Nano-3d) released the bioactive molecule menthol within the MCF-7 breast cancer cell line causing effective cytotoxicity after photorelease. Hence, this development of a fluorescein-based PRPG can contribute to advancements in dye-based image-guided nanodrug delivery systems.