Selective "turn-on" fluorescent sensing for biothiols based on fluorescence resonance energy transfer between acridine orange and gold nanoparticles

This study reports a novel fluorescence resonance energy transfer (FRET) system between acridine orange (AO) and gold nanoparticles (AuNPs), in which AO acts as the donor and AuNPs as the acceptor. In this system, AO is noncovalently self-adsorbed on AuNPs, which induces fluorescence quenching of AO as a result of FRET between AO and AuNPs. The fluorescence of AO switches to "turn-on"(restore) upon the addition of thiols due to the strong interactions between the thiols and gold nanoparticles, which leads to the dissociation of AO from the surfaces of AuNPs and thus its fluorescence "turn-on". Based on the enhanced fluorescence, a homogenous assay method for sensing thiols is proposed. Under optimal conditions, the enhanced fluorescence intensity displays a linear relationship with the concentration of cysteine ranging from 2.5 x 10(-9) M to 1 x 10(-7) M with a detection limit of 0.72 nM. This method also demonstrates a high selectivity to other thiol-containing amino acids due to the strong affinity of thiols to gold, which allows the analysis of the total amount of thiol-containing amino acids in samples. The proposed approach demonstrates the feasibility of the AuNPs-based "turn-on" fluorescence sensing for total thiols in human plasma samples with satisfactory results.