Protein-activated transformation of silver nanoparticles into blue and red-emitting nanoclusters

Proteins are very effective capping agents to synthesize biocompatible metal nanomaterials in situ. Reduction of metal salts in the presence of a protein generates very different types of nanomaterials (nanoparticles or nanoclusters) at different pH. Can a simple pH jump trigger a transformation between the nanomaterials? This has been realized through the conversion of silver nanoparticles (AgNPs) into highly fluorescent silver nanoclusters (AgNCs) via a pH-induced activation with bovine serum albumin (BSA) capping. The BSA-capped AgNPs, stable at neutral pH, undergo rapid dissolution upon a pH jump to 11.5, followed by the generation of blue-emitting Ag₈NCs under prolonged incubation (∼9 days). The AgNPs can be transformed quickly (within 1 hour) into red-emitting Ag₁₃NCs by adding sodium borohydride during the dissolution period. The BSA-capping exerts both oxidizing and reducing properties in the basic solution; it first oxidizes AgNPs into Ag⁺ and then reduces the Ag⁺ ions into AgNCs.