Selective oxidative etching of CTAC-stabilized multi-branched gold nanoparticles: application in spectral sensing of iodide ions

Multi-branched gold nanoparticles (Mb Au NPs) with sharp tips are considered excellent candidates for broad applications in plasmonics, optical sensing, and field enhancement. Here, Mb Au NPs were prepared by a one-step seedless synthesis method in the presence of Triton X-100. CTAB and CTAC were used to replace TX-100 for improving the stability of Mb Au NPs. The effect of halide ions (Cl, Br, I) on oxidative etching of CTAB- and CTAC-stabilized Mb Au NPs were investigated. The results showed that both Br⁻ and I⁻ could trigger the etching of CTAB-stabilized Mb Au NPs. However, only I⁻ triggered the etching of CTAC-stabilized Mb Au NPs even without catalysis of Cu²⁺. The selectivity of I⁻ to the etching of CTAC-stabilized Mb Au NPs led to the decrease of plasmon intensity. Based on such a unique property, we demonstrated a spectral detection method for I⁻ using the CTAC-stabilized Mb Au NPs as nanoprobes. The intensity decrease of a plasmon peak had a linear correlation with the concentration of I⁻ in the range of 1.8–18 μM, with a detection limit of 0.41 μM. The proposed method also showed a high selectivity towards I⁻ over other existing anions. Therefore, this spectral method offers the possibility to rapidly distinguish I⁻ in analytical contexts in which halide ions coexist.