33. A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu2+
Au@Ag coreeshell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu2þ) for the colorimetric sensing of iodide ion (I). This assay relies on the fact that the absorption spectra and the color of metallic coreeshell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I was added to the Au@Ag coreeshell NPs-Cu2þ system/solution, Cu2þ can oxidize I into iodine (I2), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core eshell 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 mM, and it exhibited excellent selectivity for I over other common anions tested. Furthermore, Au@Ag coreeshell NPs-Cu2þ was embedded into agarose gels as inexpensive and portable “test strips”, which were successfully used for the semi-quantitation of I in dried kelps.