Glutathione Disulfide as a Reducing, Capping, and Mass-Separating Agent for the Synthesis and Enrichment of Gold Nanoclusters

Qianqian Zhang,Zhao Meng,Hang Ren,Na Shao,Zhenglong Wu,Junhua Wang,Weidong Qin,Rui Ling

doi:10.3390/nano11092258

Abstract

Water-soluble nanoclusters, which are facilely enrichable without changes in the original properties, are highly demanded in many disciplines. In this contribution, a new class of gold nanoclusters (AuNCs) was synthesized using glutathione disulfide (GSSG) as a reducing and capping agent under intermittent heating mode. The as-prepared GSSG–AuNCs had a higher quantum yield (4.1%) compared to the conventional glutathione-protected AuNCs (1.8%). Moreover, by simply introducing the GSSG–AuNC solution to acetonitrile at a volume ratio of 1:7, a new bottom phase was formed, in which GSSG–AuNCs could be 400-fold enriched without changes in properties, with a percentage recovery higher than 99%. The enrichment approach did not need additional instruments and was potentially suitable for large-scale enrichment of nanoclusters. Further, density functional theory calculations indicated that the hydrogen bonding between GSSG and acetonitrile plays a key role for the bottom phase formation. Our work suggests that the highly emissive GSSG–AuNCs possess great potential not only in fluorescent measurements but also in other scenarios in which high-concentration AuNCs may be needed, such as catalysis, drug delivery, and electronic and optical industries.

Highlights

IntroductionUnlike other nanomaterials that are synthesized with relatively strong reductants [3,4], water-soluble gold nanoclusters (AuNCs) are synthesized using weak reducing reagents, including phosphoniums, folic acid, amino acids, peptides, Good’s buffers, proteins, exosomes, and thiolates [5,6,7,8,9,10]
GSSG, a new mass-separating agent found by this work, may find its place in enrichment of nanoclusters and in other disciplines such as separation and extraction
Note that in the widely adopted protocols for preparing the GSH-protected AuNCs, the initial concentration of HAuCl4 was 2 mM [35]; the influence of the concentration ratio between GSSG and HAuCl4 in this experiment was investigated by keeping HAuCl4 at 2 mM, while varying the concentration of GSSG for rational comparison

Summary

Introduction

Unlike other nanomaterials that are synthesized with relatively strong reductants [3,4], water-soluble gold nanoclusters (AuNCs) are synthesized using weak reducing reagents, including phosphoniums, folic acid, amino acids, peptides, Good’s buffers, proteins, exosomes, and thiolates [5,6,7,8,9,10]. Compared with the conventional fluorescent dyes, fluorescent proteins, quantum dots, carbon nanodots, and upconverting lanthanide-doped nanoparticles, GSH–AuNCs have the advantages of low toxicity, excellent cell membrane permeability, and good biocompatibility. They possess a low quantum yield (QY) [11] and a low molar extinction coefficient that result in poor luminescence.

Methods

Results

Conclusion