4-Amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles as fluorophore for the ultrasensitive and selective determination of l-cysteine

Abstract

The present study reports the highly sensitive and selective determination of l-cysteine (Cys) using 4-amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles (AHMP-AuNPs) by spectrofluorimetry. The AHMP-AuNPs were synthesized by wet chemical method and were characterized by UV–visible, HR-TEM, XRD, FT-IR, zeta potential and spectrofluorimetry. They show emission maximum at 781nm while exciting at 520nm and a large stock shift (261nm) with a narrow emission profile besides good photostability. On adding 1.75μM Cys to AHMP-AuNPs, the wine red color was changed to purple and a new absorption peak was appeared at 670nm. This is due to the aggregation of AHMP-AuNPs and it was confirmed by HR-TEM. The absorption band of AHMP-AuNPs does not change while adding less than micromolar concentration of Cys. However, the emission intensity of AHMP-AuNPs was enhanced even in the presence of picomolar concentration of Cys. Based on the enhancement of emission intensity, the concentration of Cys was determined. The present fluorophore showed an extreme selectivity toward the determination of Cys in the presence of 10,000-fold of all other l-amino acids. This is due to the specific interaction of Cys with AHMP-AuNPs via Au–S bond because it is the only amino acid contains –SH group when compared to all other amino acids. A good linearity was observed from 10 to 130pM Cys and a detection limit was found to be 110fmolL−1 (S/N=3). The present method was successfully used for the determination of Cys in real samples.