Multicolor fluorescence dynamic switching of gold nanoclusters by pH-induced core-shell interfacial regulation.

Understanding the interface regulation process of the core-shell structure is of great significance for tailoring single ligand-engineered gold nanoclusters (Au NCs) and achieving pH-responsive multi-color fluorescence control switching. In this study, multicolor fluorescence switchable Au NCs are synthesized using cysteine as a single ligand with varying pKa values, promoting gold ion growth on cellulose nanocrystals (CNCs). The shell layer of AuNCs is rich in thiol, carboxyl, and amino groups, which deprotonate gradually as the pH increases from 3 to 11, inducing a conformational reorganization of the outer layer of the AuNCs, altering the Au(0)/Au(I) ratio and causing a shift in the fluorescence emission. The AuNCs exhibits reversible pH-dependent fluorescence switching: from pink dual-emission at around 410 and 625 nm pH = 3, to orange-yellow at around 610 nm pH = 9, and green fluorescence at around 520 nm pH = 11. CNCs act as templates and stabilizers, enhancing the fluorescence quantum yield and improving stability for up to 1.5 years. This work significantly enhances understanding of the pH induced core-shell structure reconstruction process of AuNCs, while stimulating innovations in controllable regulation of multi-color fluorescence dynamic switching of nanoclusters, with potential applications in dynamic information encryption.