Ayed, Z. | Search bioRxiv

bioRxiv2025

Self-Assembled siRNA-Gold Supraclusters Detected at the Single-Molecule Level in the NIR-II Window

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.

bioengineering↗

bioRxiv2025

Interplay Between Intrinsically Disordered Proteins and Atomically Precise Gold Nanoclusters Modulates their Optical Properties

Understanding how structural and optical properties of metallic nanoclusters can be tuned by proteins is crucial for the use of these hybrid molecules in biomedical applications. The interaction of proteins with ultrasmall, atomically-precise gold nanoclusters (Au-NCs) has been mainly investigated in the context of structured proteins, while their behavior with intrinsically disordered proteins (IDPs) remains unexplored. This work examines the structural and optical properties of Au-NCs interacting with bioengineered IDPs containing up to three cysteines. We show that, by exploiting the conformational flexibility of cysteine-containing IDPs, we can anchor proteins to Au-NCs in a position-specific manner, leading to new bioconjugates with properties that differ from those of the individual components. We observed an up to 15-fold photoluminescence enhancement depending on the number of cysteines anchored. By combining mass spectrometry, small-angle X-ray scattering (SAXS), and computational modelling, the ensemble structures of nine bioconjugates with different stoichiometries were elucidated, indicating their overall compactness. Our results suggest that the interface between these atomically-precise species and the conformationally fluctuating protein is responsible for the optical properties of these nanobioconjugates. This research improves our understanding of Au-NC- protein interactions, paving the way to novel nano-molecular hybrid conjugates with tunable properties for bioimaging and therapeutic applications.

biochemistry↗