Shrinking gold nanoparticles: dramatic effect of a cryogenic process on tannic acid/sodium citrate-generated gold nanoparticles

Aqueous gold nanoparticles (Au-NPs) without surfactant protection undergo irreversible aggregation upon a cryogenic treatment. However, a cryogenic process on aqueous gold nanoparticle solution containing tannic acid did not lead to nanoparticle aggregation. The tannic acid serves as surfactant to prevent aggregation of gold nanoparticles. In contrast, a reduction in the particle size in this solution containing tannic acid was observed upon the cryogenic treatment with good reproducibility and uniformity.