Ultrasensitive L-methionine functionalized AuNPs for colorimetric and UV–vis dual-mode parallel detection of As³⁺, Cd²⁺ and Hg²⁺

In this work, we employed L-methionine (L-M) as the functionalized reagent of AuNPs for the colorimetric and UV–vis dual-mode detection of As³⁺, Cd²⁺, and Hg²⁺ ions with excellent selectivity and anti-interference. After adding the target ions, the functionalized AuNPs can be cross-linked together due to the As³⁺/Cd²⁺/Hg²⁺ ions reacting with amino N, carbonyl or hydroxyl O of L-methionine to form the coordination bonds, resulting in the aggregation of functionalized AuNPs and cause the different red-shifts of the SPR absorption peak and color changes of functionalized AuNPs solutions. The LODs of the colorimetric sensor are 10 ppb/13 ppb/4 ppb by naked eyes and 2.35 ppb/1.68 ppb/0.32 ppb by UV–vis spectroscopy with good linear relationships between the absorbance ratios (A_633nm/A_519nm, A_645nm/A_519nm and A_665nm/A_519nm) and As³⁺, Cd²⁺ and Hg²⁺ concentrations, which can be successfully applied to sense and detect As³⁺/Cd²⁺/Hg²⁺ pollutants in tap water, pond water, well water, and other domestic water sources.