Preparation of multi-coloured different sized fluorescent gold clusters from blue to NIR, structural analysis of the blue emitting Au7 cluster, and cell-imaging by the NIR gold cluster

Abstract

Blue, green, orange-red, red and NIR emitting gold quantum clusters have been prepared in aqueous media by using a bioactive peptide glutathione (reduced) at physiological pH. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) analyses show that the core structure sizes of the five different gold clusters are Au₇ (blue), Au₁₆ (green), Au₁₉ (orange-red), Au₂₁ (red) and Au₂₂ (NIR). The photo-stability and pH-stability of these quantum clusters have been measured, and these are photo-stable against continuous UV irradiation for a few hours. They also exhibit moderate to good pH-stability within the pH range of 5–12.5. A computational study reveals the organisation of gold atoms in the thiolate-protected blue quantum cluster and its several structural parameters, including the mode of interaction of ligand molecules with Au atoms in the Au₇ cluster. Interestingly, it has been found that NIR emitting gold quantum cluster can easily be internalized into the adenocarcinomic human alveolar basal epithelial cell line (A549 cell line). Moreover, a MTT assay indicates that our NIR emitting gold quantum cluster show very low cytotoxicy to A549 cancer cells.