Fluorescent gold nanoclusters (Au NC) are a promising turn-off probe material for selective chemical sensing. However, low quantum yields (QY) and a limited understanding of the mechanistic origin of the fluorescence limit their practical implementation. Using a physical mixing process based on polymer-salt aggregate (PSA) self-assembly chemistry, we induced glutathione-stabilized Au NCs to aggregate within silica-coated microcapsular structures. This material exhibits a fluorescence QY of 29%, double that of unencapsulated Au NCs with a five-fold enhancement of emission intensity at 600 nm, consistent with the expectations of the aggregation-induced emission (AIE) phenomenon. This approach increased the limit of detection (LOD) for our target contaminant, chromium-6 (Cr(VI)), from 1 μM (0.2 ppm) when the Au NCs were unencapsulated to 0.05 µM (0.01 ppm) when encapsulated; this LOD is 10× lower than the US EPA regulation for total chromium (Cr(III) + Cr(VI)) in drinking water. Furthermore, encapsulated Au NCs can detect Cr(VI) without the external pH adjustment that would otherwise be necessary, due to the low-pH conditions inside the capsules. This material may be a general means to sense and quantify Cr(VI) and serve as a model for similar, practical ion-sensitive sensors at sub-micromolar concentrations.

Charge-assembled fluorescent gold microcapsules with enhanced chromium(VI) sensitivity

255th National Meeting (2018)

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