Multiplex detection of halide ions in Water: Feasibility of Optoelectronic Tongues using Au@Ag nanorod multicolor patterns

[Display omitted] •Au@Ag nanorod-based multicolor patterns for multiplex detection of halide.•Halide-induced inhibition silver nanoshell growth on gold nanorods.•Machine-learning assisted quantification and identification of halides. Halide anions pose significant environmental threats due to their toxicity and corrosive nature. Effective environmental surveillance hinges on the accurate identification and quantification of these anions in water samples. This investigation focuses on developing a colorimetric sensor array that can simultaneously identify and quantify halide anions in water. Leveraging the silver metallization strategy of gold nanorods (AuNRs@Ag), we have fabricated cross-reactive plasmonic sensor elements tailored for anion detection. The distinct redox potentials, formation constants, and solubility constants of halide ions with silver (Ag+) ions modulate the formation of silver shells on AuNRs. These interactions alter the deposition thickness of the silver layer on the AuNRs’ surface, leading to blue shifts in the localized surface plasmon resonance (LSPR) peak and a spectrum of color changes from red to green, blue, and purple. These color shifts enable the discrimination of various halide anions. Employing machine-learning techniques such as linear discriminant analysis (LDA) and partial least squares (PLS) regression, we analyzed the fingerprint absorption profiles of AuNRs@Ag upon the addition of different concentrations of halide ions. The designed sensor array exhibited linear responses to halides ion solution over a broad concentration range:40–250, 130–8000, 40–2000 and 10–1000 μmol/L, with detection limits of 36.8, 122.4, 30.33 and 15.8 μmol/L for F−, Cl−,Br− and I−respectively. This study underscores the potential of a multi-colorimetric sensor array for rapid and precise detection of halide ions in water, with significant implications for environmental monitoring and water quality assessment.