ph‐Dependent Synthesis of Pepsin‐Mediated Gold Nanoclusters with Blue Green and Red Fluorescent Emission

Abstract

This report demonstrates the fi rst pH-dependent synthesis of pepsinmediated gold nanoclusters (AuNCs) with blue-, green-, and red-fl uorescent emission from Au 5 (Au 8 ), Au 13 , and Au 25 , respectively. Pepsin is a gastric aspartic proteinase (molecular weight, 34 550 g/mol) that plays an integral role in the digestive process of vertebrates. It was found that the pH of the reaction solution was critical in determining the size of Au NCs (i.e., the number of gold atoms of AuNCs). Interestingly, enzyme function of pepsin contributes to the formation of these AuNCs. The photo-stability of the Au 25 (or Au 13 ) NCs is much higher than that of Au 5 NCs (i.e., Au 25 ∼ Au 13 > > Au 5 ). The pepsin-mediated Au 25 NCs were also found to be useful as fl uorescent sensors for the detection of Pb 2 + ions by enhanced fl uorescence and the detection of Hg 2 + ions by fl uorescence quenching. Although the detailed formation mechanisms of these AuNCs require further analysis, the synthetic route using proteinase demonstrated here is promising for preparing new types of fl uorescent metal nanoclusters for application in catalysis, optics, biological labeling, and sensing.

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.…”

“…Nevertheless, investigation on the oxidation state of gold suggested that Au I and Au 0 could be both present in the clusters [14][15][16]18], which implicates that different residues are involved in the process. It has been demonstrated that cysteine is not the only amino acid by which Au I species can be formed: methionine can also reduce gold salts in a similar manner [27,28].…”

Blue emitting gold nanoclusters templated by poly-cytosine DNA at low pH and poly-adenine DNA at neutral pH

“…The synthesis of AuNCs at various pH in the presence of pepsin was recently reported, where a broad range of emission colors were obtained. 19 The AuNCs prepared with A30 has a slightly longer emission peak centered at ~480 nm ( Figure 3E). The 5 excitation spectrum shows a peak at 280 nm, which is 20 nm longer than the absorption peak of poly-A DNA.…”

Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

“…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].…”