Bright, NIR‐Emitting Au₂₃ from Au₂₅: Characterization and Applications Including Biolabeling

Abstract

A novel interfacial route has been developed for the synthesis of a bright-red-emitting new subnanocluster, Au(23), by the core etching of a widely explored and more stable cluster, Au(25)SG(18) (in which SG is glutathione thiolate). A slight modification of this procedure results in the formation of two other known subnanoclusters, Au(22) and Au(33). Whereas Au(22) and Au(23) are water soluble and brightly fluorescent with quantum yields of 2.5 and 1.3 %, respectively, Au(33) is organic soluble and less fluorescent, with a quantum yield of 0.1 %. Au(23) exhibits quenching of fluorescence selectively in the presence of Cu(2+) ions and it can therefore be used as a metal-ion sensor. Aqueous- to organic-phase transfer of Au(23) has been carried out with fluorescence enhancement. Solvent dependency on the fluorescence of Au(23) before and after phase transfer has been studied extensively and the quantum yield of the cluster varies with the solvent used. The temperature response of Au(23) emission has been demonstrated. The inherent fluorescence of Au(23) was used for imaging human hepatoma cells by employing the avidin-biotin interaction.

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

“…Herein, we report for the fi rst time a pH-dependent synthesis of AuNCs with blue (Au 5 and Au 8 ), green (Au 13 ) and red (Au 25 ) fl uorescent emission using porcine pepsin, as shown in Figure 1 a. Porcine pepsin is a gastric aspartic proteinase (molecular weight, 34 550 g/mol) that plays an integral role in the digestive process of vertebrates. [ 17 ] Pepsin is unique in that it has a great predominance of acidic amino acids and high tyrosine content.…”

Synthesis of DNA-templated fluorescent gold nanoclusters

“…Alternatively, top-down etching of preformed large nanoparticles down to desired NC sizes has received much attention due to many available synthetic strategies for the large nanoparticles. In this aspect, polyethylenimine [38], dihydrolipoic acid [39,40], thiols [41][42][43], Good's buffers [44], cyclodextrins [45], and even hydrochloric acid [46] have been employed as effective etchants. Recently, large nanoparticles have been reported to be even fluorescent after being sensitized by thiols [47,48].…”

Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

“…The light absorption and emission result from electronic transitions between discrete energy levels. Well-defined AuNCs show characteristic absorption features [15]. For example, Zhu et al reported that thiolprotected Au 25 NCs showed multiple molecular-like transitions in their optical absorption spectrum owing to strong quantum size effects [16].…”