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

Xiangfei Li,Zhiwei Li,Yongjun Sun,Li Qi,Juan Qiao

doi:10.1186/s40543-021-00266-6

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.

Highlights

Folic acid (FA), composed of pteridine, p-aminobenzoic acid and L-glutamic acid, is widely used for the treatment of megaloblasticanemias, and is an essential vitamin required for the healthy functioning of all cells (Mangas et al 2004), and is especially important for pregnant women
Some of the synthesis procedures were time-consuming, it demonstrated that the use of different ligands as the reducing and stabilizing agents could result in different optical properties of the prepared Gold nanoclusters (AuNCs)
The decrease in fluorescence intensity of D-Trp-OMe@AuNCs and D-Trp-OBzl@AuNCs might be due to their large steric hindrance, which affected the formation of a compact ligand shell (Porret et al 2019)

Summary

Introduction

Folic acid (FA), composed of pteridine, p-aminobenzoic acid and L-glutamic acid, is widely used for the treatment of megaloblasticanemias, and is an essential vitamin required for the healthy functioning of all cells (Mangas et al 2004), and is especially important for pregnant women. It has been reported that the electron-rich ligands can donate their delocalized electrons to the gold core, which influences the fluorescence of AuNCs as strengthening the charge transfer from the ligand shell to the gold core can lead to improved AuNCs fluorescence emission efficiency (Wu and Jin 2010; Porret et al 2019) These approaches have proved that the fluorescence intensity and emission wavelength of AuNCs can be tuned by the type of ligands, the synthesis of AuNCs with strong fluorescence by using Damino acids and their derivatives as the ligands for highly selective monitoring of FA has not been explored until now

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Conclusion