Ultrasensitive platform for the determination of biothiols using aggregation-induced emission of gold-cysteine nanosheets

Highly ordered ultrathin nanosheets (NSs) of Au(I)-Cys were fabricated through aggregation-induced supramolecular self-assembly triggered by an extended agitation in an alkaline environment. The synthesized Au(I)-Cys NSs exhibited intense luminescence and exceptional chirality. Remarkably, additions of biothiols to Au(I)-Cys NSs have significantly enhanced their luminescence emission, and circular dichroism properties coupled with morphological modulations into nanoflowers, nanodendrites, or closely packed aggregates. These new findings of Aggregation-Induced Luminescence Enhancement (AIEE) and Aggregation-Induced Circular Dichroism Enhancement (AICE) were attributed to multiple interactions involved such as Au-S bonding, stacked H-bonding, and strong aurophilic Au(I)···Au(I), ligand-metal-charge-transfer (LMCT) and ligand-metal-metal-charge-transfer (LMMCT). The AIEE phenomenon of the fabricated Au(I)-Cys NSs was utilized for developing a highly sensitive luminescent platform for determining homocysteine (Hcy), cysteine (Cys), and glutathione (GSH) biothiols in human serum. The developed platform is simple, fast, sensitive, and highly selective for the determination of biothiols through the concentration ranges of (0.25–100.0 μM), (0.625–40.0 μM), and (5.00–600.0 μM), with a lower detection limit (S/N = 3:1) of 0.15, 0.10 and 1.20 μM for Hcy, Cys, and GSH; respectively. Interestingly, irradiation of Au(I)-Cys NSs with a high-energy electron beam during TEM analysis led to an in-situ transformation of the Au(I)-Cys NSs into gold nanoclusters (AuNCs). This phenomenon provided an innovative bottom-up strategy for the synthesis of AuNCs that could be employed in various biological and therapeutic applications. Optimization of the applied voltage and electron beam's exposure time has been found effective in synthesizing precisely designed and size-controlled AuNCs.