Colorimetric detection of cysteine using noncrosslinking aggregation of fluorosurfactant-capped silver nanoparticles

In this work, it was found that the rapid aggregation of the nonionic fluorosurfactant-capped silver nanoparticles via noncrosslinking mechanism could be induced by cysteine, but not by other amino acids and biomolecules. The high specificity toward cysteine was due to that the nonionic fluorosurfactant ligands allowed for thiol–silver interaction while prohibited the binding of other functional groups on the surface of the silver nanoparticles. Based on these interesting results, we developed a novel, selective and rapid colorimetric method for the determination of cysteine by using the nonionic fluorosurfactant-capped silver nanoparticles as a probe. Under optimum experimental conditions, the calibration curve was found to be linear over the range of 1.5–6.0 μM for cysteine with a detection limit of 0.05 μM. The applicability of the proposed method has been validated by determining cysteine in human urine and plasma samples with satisfactory results. Recoveries from spiked urine and plasma samples were in the range of 94.8–111.3%.