Stability and hybridization-driven aggregation of silver nanoparticle–oligonucleotide conjugates

Gold nanoparticles are well known to form stable oligonucleotide conjugates, via thiol-metal interaction, which are capable of specific DNA-hybridization induced aggregation. Preparation of an analogous conjugate with Ag particles, except when coated with a layer of Au, has been reported to yield conjugates that are unstable in the hybridization environment. We report herein the hybridization-induced aggregation of such "bare" Ag-particle conjugates prepared via a similar facile procedure to Au with slight modification. We found that the pH during functionalization is the critical factor determining the success of preparing conjugates that remain stable throughout the functionalization process and during hybridization. We reasoned that this is a consequence of the pH-dependent charge of the oligonucleotide, and demonstrated that pH strongly affects the amount of oligonucleotides adsorbed on the particle surface, thereby imparting stability to the particles. This finding has the potential to be generalized to other metalparticle-oligonucleotide systems with borderline stability, helping to expand the repertoire of visible-range plasmon signatures useful for diagnostic application.