A plasmonic and SERS dual-mode iodide ions detecting probe based on the etching of Ag-coated tetrapod gold nanostars

In this paper, we report plasmonic spectra and surface-enhanced Raman scattering (SERS) dual-mode iodide ions (I⁻) detecting probe based on Ag-coated tetrapod Au nanostars (Au@Ag tetrapod nanostars). This probe depends on the fact that I⁻ can etch the silver layer of Au@Ag tetrapod nanostars in the presence of Cu²⁺, which leads to the red shift of in-plane localized surface plasmon resonance (LSPR) peak and decrease of SERS intensity. Indeed, our regular morphologies of Au@Ag tetrapod nanostars provide a uniform response space for the plasmonic spectral probe. The red shift caused by both the silver layer etching and gold tips exposing make the in-plane LSPR peak more sensitive to the changes of I⁻ concentration, which results in an extremely wide linear range of 0.5–280 μM. Meanwhile, when the four Au tips are not fully coated by silver layer but still exposed to outsides, the strong SERS enhancement effect from Ag coating and tip effect together leads to the lower limit of detection (LOD) of 26 nM. Furthermore, this proposed method exhibits a good selectivity for I⁻ over other ions and is well applied in dried kelp and drinking water.