Peptide-Stabilized, Fluorescent Silver Nanoclusters: Solid-Phase Synthesis and Screening.

Few-atom silver nanoclusters (AgNCs) can exhibit strong fluorescence; however, they require ligands to prevent aggregation into larger nanoparticles. Fluorescent AgNCs in biopolymer scaffolds have so far mainly been synthesized in solution, and peptides have only found limited use compared to DNA. Herein, we demonstrate how solid-phase methods can increase throughput dramatically in peptide ligand screening and in initial evaluation of fluorescence intensity and chemical stability of peptide-stabilized AgNCs (P-AgNCs). 9-Fluorenylmethyloxycarbonyl (Fmoc) solid-phase peptide synthesis on a hydroxymethyl-benzoic acid (HMBA) polyethylene glycol polyacrylamide copolymer (PEGA) resin enabled on-resin screening and evaluation of a peptide library, leading to identification of novel peptide-stabilized, fluorescent AgNCs. Using systematic amino acid substitutions, we synthesized and screened a 144-member library. This allowed us to evaluate the effect of length, charge, and Cys content in peptides used as ligands for AgNC stabilization. The results of this study will enable future spectroscopic studies of these peptide-stabilized AgNCs for bioimaging and other applications.