Silver nanoplates-based colorimetric iodide recognition and sensing using sodium thiosulfate as a sensitizer

• A new colorimetric iodide detection strategy based on triangular Ag nanoplate.
• Sodium thiosulfate performed as a sensitizer.
• Formation of insoluble AgI on the surface of Ag nanoplate.
• This method has the advantages of good selectivity and high sensitivity.

A colorimetric method for the recognition and sensing of iodide ions (I−) has been developed by utilizing the reactions between triangular silver nanoplates (TAg-NPs) and I− in the presence of sodium thiosulfate (Na2S2O3). Specifically, I− together with Na2S2O3 can induce protection of TAg-NPs owing to the formation of insoluble AgI, as confirmed by the high-resolution transmission electron microscopy (HRTEM). In the absence of Na2S2O3, the etching reactions on TAg-NPs were observed not only by I− but also other halides ions. The Na2S2O3 plays as a sensitizer in this system, which improved the selectivity and sensitivity. The desired colorimetric detection can be achieved by measuring the change of the absorption peak wavelength corresponding to localized surface plasmon resonance (LSPR) with UV–vis spectrophotometer or recognized by naked eye observation. The results show that the shift of the maximum absorption wavelength (Δλ) of the TAg-NPs/Na2S2O3/I− mixture was proportional to the concentration of I− in the range 1.0 × 10−9–1.0 × 10−6 mol L−1. Moreover, no other ions besides I− can induce an eye discernible color change as low as 1.0 × 10−7 mol L−1. Finally, this method was successfully applied for I− determination in kelp samples.

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