Fluorescence turn-off-on for highly selective detection of serum l-cysteine based on AuNCs-AuNPs ensembles.

The discriminative monitoring of biothiols in biological fluids is a great challenge. Herein, we developed a fluorescence "turn-off-on" probe based on AuNCs-AuNPs ensembles, which detected l-cysteine (l-Cys) with high selectivity. The strong blue fluorescence of l-hydroxyproline-capped gold nanoclusters (l-Hyp@AuNCs) at 465 nm was quenched by AuNPs via the inner filter effect. Interestingly, the fluorescence was recovered by interaction with l-Cys due to the electrostatic and specific Au-S interactions between l-Cys and AuNPs. The effect of the l-Cys amount on the fluorescence "off-on" efficiency showed good linearity in the range of 1.5-35.0 μM (R2 = 0.986) with a detection limit of 1.4 μM (3σ). The proposed method was successfully applied to test the serum l-Cys levels without the interference of glutathione, homocysteine and methionine. The AuNCs-AuNPs ensembles-based fluorescence "turn-off-on" protocol shows great potential in specific biothiol sensing.