Expanding the\nToolbox of Oxidants: Controllable Etching\nof Ultrasmall Au Nanoparticles toward Tailorable NIR-II Luminescence\nand Ligand-Mediated Biodistribution and Clearance

Oxidant-driven and controllable etching of small-sized\nnanoparticles\n(NPs, <i>d</i> < 3 nm) and tailorable modulation of their\noptical properties are challenging due to the high reactivity and\ncomplicated surface chemistry. Herein, we present a facile strategy\nfor highly controllable oxidative etching of ultrasmall AuNPs and\ntailorable modulation of luminescence. The proper choice of a moderate\noxidant, ClO<sup>–</sup>, could not only selectively etch the\nAu(I)-thiolate motifs from the nanoparticle surface at the subnanometer\nscale but also retained a stable metallic core structure without aggregation,\nwhich impressively prompted the wide-range luminescent switching from\nthe visible to second near-infrared (NIR-II) region. The resultant\noxidized AuNPs displayed highly luminescent NIR-II emission with a\nquantum yield of 3.0%, excellent monodispersed stability, ideal biocompatibility,\nand tunable shielding effects against protein adsorption. With those\noutstanding features, oxidized AuNPs could be utilized as nanoprobes\nfor long-lasting and in vivo bioimaging of associated metabolic behaviors\nwith distinguishable organ-specific targeting capabilities and ligand-mediated\nkinetics in nanoparticle clearance. These findings expand the toolbox\nof oxidants for the controllable synthesis of NIR-II nanoprobes and\nopen up a path for exploring diverse ligand interactions on ultrasmall\nAuNPs with organs or tissues that might advance their monitoring applications\nfor a wide range of clinically important diseases.