Cyclodextrin-stabilized Gold nanoclusters for bioimaging and selective label-free intracellular sensing of Co2+ ions

Gold nanoclusters are a new class of emerging fluorescent probes which have an immense potential for the selective detection of heavy metal ions. Herein, we propose the fabrication of glutathione protected ultra-small fluorescent gold nanoclusters in the presence of cyclodextrin for fluorescence imaging and its unique sensing capabilities. A panel of characterization was elucidated to understand the characteristics and an electronic structure of cyclodextrin capped gold nanoclusters (AuCDs). Biocompatibility and cell cycle analysis were performed for AuCDs and were found to be highly biocompatible. Furthermore, confocal laser scanning microscopy showed a cytoplasmic localization of AuCDs in L929 cells with bright red fluorescence and their complete cellular internalization was confirmed using flow cytometry. The inherent fluorescence was pH-dependent and found to be specifically quenched by the addition of Co2+ ions at pH 3.5. The AuCDs were further explored to develop a label free fluorescent probe for the selective determination of Co2+ ions in aqueous solution. The Co2+ ions were selectively detectedin aqueous solutions (0-1000 mu M) and in mammalian cells (0-800 mu M) using AuCDs as a "turn-off' sensing mechanism in which the Co2+ ions bind to the sulphur atoms, thus, resulting in the disruption of charge transfer process through Au-S bond. Thus, AuCDs could form a simple nano-sensor for a label-free detection of heavy metal ions such as Co2+ in the environment. (C) 2018 Elsevier B.V. All rights reserved

Evolution of thiol-capped gold nanoclusters into larger gold nanoparticles under electron beam irradiation

We report in situ transformation of glutathione-capped red-fluorescent gold nanoclusters (AuNCs) into larger gold nanoparticles (AuNPs) embedded on a copper grid under high energy electron beam of Field Emission Gun Transmission Electron Microscope (FEG-TEM). Electron beam irradiation causes coalescing of individual finer AuNCs into bigger discrete AuNPs as a function of electron dose rate and time. The coalescence was closely studied over time and the mechanism is discussed. The study will help to understand the structural and morphological changes that occur in AuNCs inside FEG-TEM due to prolonged electron beam exposure. (C) 2017 Elsevier Ltd. All rights reserved