A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu2+

Au@Ag core-shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu2+) for the colorimetric sensing of iodide ion (I-). This assay relies on the fact that the absorption spectra and the color of metallic core-shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I- was added to the Au@Ag core-shell NPs-Cu2+ system/solution, Cu2+ can oxidize I- into iodine (I-2), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core-shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I-. The assay only took 10 min with a lowest detectable concentration of 0.5 mu M, and it exhibited excellent selectivity for I- over other common anions tested. Furthermore, Au@Ag core-shell NPs-Cu2+ was embedded into agarose gels as inexpensive and portable test strips, which were successfully used for the semi-quantitation of I- in dried kelps. (C) 2015 Elsevier B.V. All rights reserved.