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Consideration of the water-energy-food nexus is critical to sustainable development, as 18 demand continues to grow along with global population growth. Cost-effective, 19 sustainable technologies to clean water of toxic contaminants are needed. Oxyanions 20 comprise one common class of water contaminants, with many species carrying 21 significant human health risks. The United States Environmental Protection Agency (US 22 EPA) regulates the concentration of oxyanion contaminants in drinking water via the 23 National Primary Drinking Water Regulations (NPDWR). Degrading oxyanions into 24 innocuous compounds through catalytic chemistry is a well-studied approach that does 25 not generate additional waste, which is a significant advantage over adsorption and 26 separation methods. Noble metal nanostructures, e.g., Au, Pd and Pt, are particularly 27 opportunities for metal nanostructures to contribute to improved quality and sustainability 33 of water resources.

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Luminescent gold nanoclusters (Au NCs) are a promising probe material for selective chemical sensing. However, low luminescent intensity and an incomplete understanding of the mechanistic origin of the luminescence limit their practical implementation. We induced glutathione-capped Au NCs to aggregate within silica-coated microcapsular structures using polymer−salt aggregate self-assembly chemistry. The encapsulated NCs have a 5× luminescence enhancement compared to free Au NCs and can detect Cr(VI) at concentrations as low as 6 ppb (=0.12 μM CrO 4 2− ) through luminescence quenching, compared to free Au NCs, which have a limit of detection (LOD) of 52 ppb (=1 μM CrO 4 2− ). The LOD is 16× lower than the United States Environmental Protection Agency maximum contaminant level for total chromium (Cr(III) + Cr(VI), 100 ppb) in drinking water. No pH adjustment is needed using the encapsulated Au NCs, unlike the case for free Au NCs. The luminescent microcapsule material can sense Cr(VI) in simulated drinking water with a ∼20−30 ppb LOD, serving as a possible basis for a practical Cr(VI) sensor.

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