Mixing-to-Answer Iodide Sensing with Commercial Chemicals

We develop a convenient, colorimetric assay (Au/PEI) for rapid iodide (I^–) determination that can be prepared facilely by mixing commercially available chemicals including tetrachloroauric acid (HAuCl₄) and poly­(ether imide) (PEI), and the assay can be carried out directly by adding the samples to the assay without any pretreatment and additional procedure. Au/PEI operates on the principle that I^– accelerates the formation of Au NPs, which leads to a visible color change from light yellow to red for naked-eye readout with high specificity. We integrate our assay on solid devices including gel hybrids (Au/PEI/GH) and filter paper (Au/PEI paper) to satisfy the demand of point-of-care testing and justify the practicality by detecting I^– in lake water that was supplemented with 10, 20, or 40 μM of I^–. Au/PEI/GH with the limit of detection of 0.35 μM can satisfy the detection of drinking water based on the guidelines (1.2 μM) set by the Chinese government, and Au/PEI paper can be used even after 1 year of storage. Such assays provide a convenient and straightforward choice for routine, on-site I^– tests.