Aggregated gold nanoparticles as photoactivators for the photopolymerization of proteins

Photopolymerization of bovine serum albumin was carried out using reactive oxygen species (ROS) generated by the irradiation of citrate-stabilized gold nanoparticles by a pulsed Nd³⁺:YAG laser. The ROS in this case, singlet oxygen (¹O₂), targets aromatic amino acids within the protein to induce photopolymerization or crosslinking. Other ROS, like the hydroxyl radical, can also form in solution and under high-energy irradiation. The gold nanoparticles were aggregated using different cations in order to maximize singlet oxygen production. Experimental parameters like exposure time and laser power were optimized to minimize damage and maximize crosslinking efficiency, and damage-free crosslinking was observed at laser exposures up to 60 s with samples containing calcium demonstrating most efficient crosslinking. To confirm the role of ROS in crosslinking, the reactive oxygen scavengers sodium azide and mannitol were added at different concentrations to scavenge the singlet oxygen and hydroxyl radical, respectively, and both were observed to stop or slow the formation of crosslinking. The use of gold nanoparticles offers an inert and biocompatible alternative to organic crosslinking agents like rose Bengal and methylene blue.