(Lysozyme Type VI)‐Stabilized Au₈ Clusters: Synthesis Mechanism and Application for Sensing of Glutathione in a Single Drop of Blood

Abstract

This paper presents a one-pot approach for preparing highly fluorescent Au(8) clusters by reacting the Au(3+) precursor solution with lysozyme type VI (Lys VI) at pH 3. The fluorescence band of (Lys VI)-stabilized Au(8) clusters is centered at 455 nm on the excitation at 380 nm. Blue-emitting Au(8) clusters have a high quantum yield (∼56%), two fluorescence lifetimes, and a rare amount of Au(+) on the surface of the Au core. When the pH of a solution of Au(8) clusters increases suddenly to 12, the Au(8) clusters gradually convert to Au(25) clusters over time. This conversion is also observed in the case of (Lys VI)-directed synthesis of Au(25) clusters at pH 12. The pH-induced conversion of Au(8) to Au(25) clusters suggests that the size of (Lys VI)-stabilized gold nanoclusters (AuNCs) relies on the secondary structure of Lys VI, which is susceptible to pH change. Based on these results and previous literature, this paper proposes the possible mechanism for growing (Lys VI)-stabilized Au(8) and Au(25) clusters. Additionally, (Lys VI)-stabilized Au(8) clusters could sense glutathione (GSH) through GSH-induced core-etching of Au(8) clusters; the limit of detection at a signal-to-noise ratio of 3 for GSH is determined to be 20 nm. Except for cysteine, the selectivity of (Lys VI)-stabilized Au(8) clusters for GSH over amino acids is remarkably high. The practicality of using Au(8) clusters to determine the concentration of GSH in a single drop of blood is also validated.

Human serum albumin encapsulated gold nanoclusters: effects of cluster synthesis on natural protein characteristics

“…The electrophoretic mobility was measured for all samples at a concentration of 1000ppm across a pH range of 2-11. Using H can be found [3].…”

“…Much interest has been shown in utilizing protein encapsulated gold nanoclusters (AuNCs) as fluorophores for in vitro and in vivo bio-imaging and sensing applications [1][2][3][4][5] due to the unique physical and optical properties of AuNCs. In particular in vivo selective imaging of specific cells using AuNCs has shown much promise [6][7][8] .…”

On the selection and design of proteins and peptide derivatives for the production of photoluminescent, red-emitting gold quantum clusters

“…These are bovine serum albumin (BSA), trypsin, pepsin, horseradish peroxidase, lactoferrin, human serum transferrin, lysozyme, and cellular retinoic acid-binding protein 2 (CRABP2) [14][15][16][17][18][19][20][21]. Proteinconjugated gold clusters are already applied as analytical sensors of Hg 2+ , Pb 2+ moreover, BSA-protected clusters do not show significant toxicity in vitro [25], which allows their application in biological systems.…”

Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

“…During the synthesis of NCs, Au 3? ions are mainly reduced by the 21 tyrosine residues in BSA through the phenolic groups. Tseng's group presented a novel approach for preparing highly fluorescent Au 8 NCs and Au 25 NCs by using lysozyme type VI (Lys VI) at pH 3 and pH 12, [43] respectively [49]. Inspired by this finding, researchers try to explore other proteins as efficient bioscaffolds for synthesizing AuNCs such as insulin [50], transferrin-family proteins [51,52], horseradish peroxidase [53], pepsin [54], denatured BSA [55], ribonuclease A [56], trypsin [57], DNase I [58], ovalbumin [59], and egg white [60].…”