Photo-induced growth of DNA-capped silver nanoparticles

We report the photo-induced nucleation and growth of silver nanoparticles in aqueous solution in the presence of DNA oligomers. An organic dye (Cy5) was used as a photosensitizer to initiate the nanoparticle growth upon illumination with 647 nm light. The formation of nanoparticles and growth kinetics were observed by extinction spectroscopy, dynamic light scattering, and transmission electron microscopy. Irradiation of the precursor solutions with light at the Cy5 absorption maximum triggered the instantaneous formation of spherical particles with a metallic core ~15 nm in diameter. Remarkably, the particles feature significantly larger effective hydrodynamic diameters (35 nm) in solution, indicative of a DNA ad-layer on the nanoparticle surface. Centrifugation experiments confirmed that DNA was inseparably associated with the nanoparticles and indicated that DNA oligomers adsorb onto the nanoparticle surface during growth, playing the role of a capping agent. The introduced method is a fast and facile way to prepare DNA-capped silver nanoparticles in a single growth step.