Tandem photo-crosslinking/sol–gel reaction for the green synthesis of morphology-alterable, redox-responsive silica particles

Abstract

Silica-based nanoparticles have been employed in versatile biomedical applications during the past decades and one of the important research focuses has been the synthesis of biothiol-degradable redox responsive silica to resolve the toxicity concerns of bioaccumulation. In the conventional sol-gel approach, the use of acidic or basic catalyst was always necessary. Solvent, heating, and templates were often applied. Besides, multi-step synthetic procedures were also frequently required to obtain the desired silane with disulfide-linkage for the following synthesis. We developed a facile and green photo-crosslinking coupled sol–gel reaction to produce disulfide-linked redox-responsive silica particles in water at room temperature. The reaction was template-free and initiated by visible light irradiation of photosensitizer (rose bengal). The particle size was tunable by adjusting the concentration of silica precursors, photosensitizer, and irradiation time of LED. The morphologies of the silica nanoparticles can be dramatically altered by simply changing the thiolated silica precursors. The kinetics of the silica precursors during the hydrolysis and photocrosslinking reactions played a critical role. Rose bengal served as a photosensitizer for silica nanoparticle formation and a photodynamic drug. The encapsulated rose bengal remained effective to generate singlet oxygen with superior performance than that of free ones. The disulfide bonds created in the silica matrix responded to reducing reagents, resulting in controllable self-disassembly. Additionally, we found that the presence of magnesium salts affected the rate of the photocrosslinking reaction, forming rod-shaped particles. The current results provide insights for future stimuli-responsive silica-based material development.