Phase-Separated Condensates of Atomically Precise Nanoclusters Enable Direct Visualization of Nano-Bio Interactions.

Liquid-liquid phase separation (LLPS) underpins the formation of membrane-less organelles (MLOs), particularly those involving intrinsically disordered proteins, and is increasingly recognized as a fundamental mechanism of cellular organization. Emulating such behavior in synthetic inorganic systems remains a central challenge in materials science. Herein, we demonstrate that atomically precise gold nanoclusters, Au22(SG)18 (where -SG represents glutathione), undergo LLPS in the presence of a macromolecular crowder, poly(ethylene glycol). Extended structural motifs present in the structure of Au22(SG)18 promote condensation under crowding conditions, yielding "nanoparticle condensates" with aggregation-induced emission characteristics that permit real-time visualization and fluorescence recovery after photobleaching (FRAP) analysis. These condensates exhibit hallmark features of biomolecular condensates, including liquid-like dynamicity and reversibility. In protein-rich environments, Au22(SG)18 displays a spectrum of phase behaviors: independent phase separation with mucin, partial co-condensation with γ-globulin, and robust heterotypic LLPS with bovine serum albumin (BSA), lysozyme, and β-lactoglobulin. Confocal laser scanning microscopy (CLSM) imaging and FRAP analysis reveal that protein co-condensation can modulate condensate diffusivity, with shared compartments dampening dynamics and distinct ones enhancing them. Our findings highlight atomically precise nanoclusters as a powerful alternative luminescent analogue for dissecting biomolecular LLPS and elucidating nanobio interactions.