Carbon dots-silver nanoparticles fluorescence resonance energy transfer system as a novel turn-on fluorescent probe for selective determination of cysteine

• Interaction of carbon dots with AgNPs was investigated.
• The fluorescence of C-dots is efficiently quenched by AgNPs.
• C-dot-AgNP FRET system was used as a selective turn-on sensor for cysteine.
• Using this system the LOD of 6.0 nM was obtained for cysteine.

In this paper, we investigated the interaction of carbon dots (C-dots) prepared from orange juice with silver nanoparticles (AgNPs) using fluorescence spectroscopy. It was found that AgNPs efficiently quench the fluorescence of C-dots as a result of fluorescence resonance energy transfer (FRET). Thus, a novel FRET system between C-dots (as the donor) and AgNPs (as the acceptor) was introduced. Moreover, it was found that cysteine even at nanomolar levels could recover the fluorescence of C-dots due to the competitive adsorption of this compound onto AgNPs. This was exploited to design a simple and selective method for the determination of cysteine in the concentration range from 6.0 to 300 nM, with a detection limit of 4.0 nM. Cysteine was determined by this method in human plasma and urine samples with satisfactory results.