Ayed, Z.; Martin Munoz, B.; Vandekerckhove, C. I.; Faure, V.; Ali, S. N. S.; Coll, J.-L.; Cognet, L.; Le Guevel, X.

Gold nanoclusters (AuNCs) possess unique photophysical properties that make them excellent candidates for advanced bioimaging and single-particle detection. In this work, we report the self-assembly of highly emissive, positively charged NIR-II AuNCs stabilized by cysteamine, directed by small interfering RNA (siRNA), which serves as both a structural and electrostatic modulator. The resulting supramolecular assemblies exhibit quasi-spherical morphologies around 100 nm in diameter, with outstanding colloidal stability, photostability, and enzymatic resistance. Their strong photoluminescence, extending up to 1400 nm, enables robust single-particle detection in solution. Spectroscopic and structural analyses, including fluorescence spectroscopy, small-angle X-ray scattering (SAXS), and single-particle tracking, highlight the pivotal role of siRNA in tuning the assembly process via charge balance and concentration-dependent interactions. Beyond providing insights into the structural and photophysical behavior of nucleic acid-guided AuNC assemblies, these results underscore their promise as multifunctional nanoplatforms for integrated imaging and gene-silencing therapies in biophotonic and theranostic applications.