Ultrasmall gold and platinum nanoparticles (≈2 nm) possess unique physicochemical properties that enable cellular uptake and even passage across the blood–brain barrier, rendering them attractive for biomedical and biosensing applications. Despite their potential, strategies for precise surface functionalization and controlled nanoparticle assembly remain limited.

In this work, ultrasmall nanoparticles were synthesized in aqueous media, stabilized with glutathione, and subsequently azidated. The introduced azide groups allowed site-specific modification via copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC), enabling covalent conjugation with alkyne-terminated oligonucleotides. Fluorescent dyes (FAM, Cy3) were incorporated to probe hybridization processes through Förster resonance energy transfer (FRET).

Comprehensive characterization by HRTEM, NMR, IR, DCS, UV/Vis, and fluorescence spectroscopy confirmed successful functionalization and stability of the conjugates. Hybridization studies demonstrated efficient duplex formation between complementary sequences, both in free oligonucleotides and when attached to nanoparticles. Moreover, DNA-directed interactions mediated the assembly of nanoparticle multimers with defined architectures.