We have found that lysozyme crystallization is promoted by gap-mode surface plasmon resonance of gold nanoparticles (AuNPs). Crystallization experiments were performed by dropping a metastable lysozyme solution in a supersaturated state in which spontaneous nucleation does not occur onto substrates prepared by dropping a 40 nm diameter AuNPs colloidal solution onto a glass substrate and subsequent drying. These substrates were capable of inducing gap-mode surface plasmon resonance. Crystals were deposited on the prepared substrates in numbers that increased with light irradiation, whereas none were deposited on control substrates. A crystallization mechanism involving lysozyme adsorption on AuNPs was proposed. The results showed that the number of lysozyme molecules adsorbed on the AuNPs corresponded well to the number of deposited crystals.
