Using L‐Arginine‐Functionalized Gold Nanorods for Visible Detection of Mercury(II) Ions

A rapid and simple approach for visible determination of mercury ions (Hg²⁺) in aqueous solutions was developed based on surface plasmon resonance phenomenon using L‐arginine‐functionalized gold nanorods (AuNRs). At pH greater than 9, the deprotonated amine group of L‐arginine on the AuNRs bound with Hg²⁺ leading to the side‐by‐side assembly of AuNRs, which was verified by transmission electron microscopy images. Thus, when Hg²⁺ was present in the test solution, a blue shift of the typical longitudinal plasmon band of the AuNRs was observed in the ultra violet‐visible‐near infrared (UV‐Vis‐NIR) spectra, along with a change in the color of the solution, which occurred within 5 min. After carefully optimizing the potential factors affecting the performance, the L‐arginine/AuNRs sensing system was found to be highly sensitive to Hg²⁺, with the limit of detection of 5 nM (S/N = 3); it is also very selective and free of interference from 10 other metal ions (Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cs⁺, Cu²⁺, K⁺, Li⁺, Ni²⁺, Pb²⁺). The result suggests that the L‐arginine‐functionalized AuNRs can potentially serve as a rapid, sensitive, and easy‐to‐use colorimetric biosensor useful for determining Hg²⁺ in food and environmental samples.