Ligand-modulated synthesis of gold nanoclusters for sensitive and selective detection of folic acid

Abstract

Precisely changing the optical properties of gold nanoclusters (AuNCs) with different ligands offers a promising prospect for highly sensitive and selective drug sensing. In this study, AuNCs were synthesized with d-tryptophan (d-Trp) and its derivatives as the ligands. Optical measurements showed that d-Trp@AuNCs produced higher fluorescence intensity and shorter fluorescence emission wavelength than the d-Trp-derivatives-ligands protected AuNCs, indicating that the ligand-shell rigidity and core-shell charge transfer affected their fluorescent properties. At the excitation wavelength of 370 nm, the emission wavelength of d-Trp@AuNCs was 460 nm. The fluorescence changes revealed the high selectivity of d-Trp@AuNCs for detecting folic acid due to the static quenching and inner filter effect. In the presence of folic acid, the fluorescence of d-Trp@AuNCs was remarkably quenched with good linearity ranging from 6.3-100.0 μM (R2 = 0.997) and a detection limit of 5.8 μM. The proposed assay was successfully utilized to determine the amount of folic acid in human urine with recoveries from 94.3 to 107.3%. This work shows the great potential of d-Trp@AuNCs for detecting folic acid in real bio-samples. It also presents an effective strategy for preparation of the AuNCs with enhanced fluorescence efficiency by regulating the rigidity of the ligands shell and the core-shell charge transfer.