Highly selective and sensitive detection of cysteine with a graphene quantum dots-gold nanoparticles based core-shell nanosensor

Abstract

Reduced graphene quantum dots (r-GQDs) coated gold nanoparticles (AuNPs) core-shell structure is developed as a nanosensor for highly selective and sensitive colorimetric detection of cysteine. The reduction of nitrogen doped GQDs (N-GQDs) by NaBH4 produces r-GQDs, which serve as reductant for facilitating the conversion of HAuCl4 to AuNPs. The abundant hydroxyl groups and amino groups of r-GQDs not only promote the reduction of Au (III) into Au (0), but also facilitate the effective coating of r-GQDs onto AuNPs. The obtained core-shell structured AuNPs@r-GQDs are well dispersed and exhibit an intensive surface plasma band at 525nm. After the adsorption of Ag+ on the surface of AuNPs@r-GQDs, cysteine as cross-linking agent induces the aggregation of AuNPs@r-GQDs and leads to their color change, which allows the sensitive colorimetric detection of cysteine and offers a detection limit low to 5.6nM. More importantly, AuNPs@r-GQDs nanosensor exhibits very high detection selectivity towards cysteine against glutathione (GSH), even at a GSH concentration of 10000-fold higher than that of cysteine. The practicability of this nanosensor is demonstrated by the discriminative determination of cysteine in human plasma.