Radical-Mediated Spin-Transfer on Gold Nanoclusters Driven an Unexpected Luminescence for Protein Discrimination

Gold nanoclusters (Au NCs) have attracted great interest for unique size-dependent properties, and more properties and applications are still encouraged to be explored and understood. Here we observed an unexpected emission from luminol upon injection of Au NCs, which did not require excitation, strong alkaline-pH regulation, or addition of oxidants, being different from the traditional fluorescence and chemiluminescence. On the basis of both experimental and computational data, the emission was shown to be generated from radical-mediated spin-transfer on Au NCs. Species of O₂^•- were identified as primary radicals that triggered the spin-transfer from the triplet state of O₂ to the aminobenzene ring of luminol by the aids of Au NCs, leading to an efficient phosphorescence. Subsequently, a sensor array composed of five protein-protected Au NCs was fabricated for protein discrimination. This work not only provides new insights of Au NCs into luminol emission but also shows potentials in protein discrimination.