A colorimetric nitrite detection system with excellent selectivity and high sensitivity based on Ag@Au nanoparticles

Abstract

Excessive uptake of NO₂⁻ is detrimental to human health, but the currently available methods used to sensitively detect this ion in the environment are cumbersome and expensive. In this study, we developed an improved NO₂⁻ detection system based on a redox etching strategy of CTAB-stabilized Ag–Au core–shell nanoparticles (Ag@AuNPs). The detection mechanism was verified by UV-Vis spectroscopy, TEM and XPS. The detection system produces a color change from purple to colorless in response to an increase of NO₂⁻ concentration. The selectivity of detection of NO₂⁻, both with the unaided eye and by measurement of UV-Vis spectra, is excellent in relation to other ions, including Cu²⁺, Co²⁺, Ni²⁺, Cr³⁺, Al³⁺, Pb²⁺, Cd²⁺, Ca²⁺, Ba²⁺, Zn²⁺, Mn²⁺, Mg²⁺, Fe³⁺, Hg²⁺, Ag⁺, K⁺, F⁻, PO₄³⁻, C₂O₄²⁻, SO₃²⁻, CO₃²⁻, SO₄²⁻, NO₃⁻ and CH₃–COO⁻ (Ac⁻). The limit of detection (LOD) for NO₂⁻ is 1.0 μM by eye and 0.1 μM by UV-Vis spectroscopy. The LOD by eye is lower than the lowest previously reported value (4.0 μM). There is a good linear relationship between A/A₀ and the concentration of NO₂⁻ from 1.0 to 20.0 μM NO₂⁻, which permits a quantitative assay. The applicability of our detection system was also verified by analysis of NO₂⁻ in tap water and lake water. The results demonstrate that our Ag@AuNP-based detection system can be used for the rapid colorimetric detection of NO₂⁻ in complex environmental samples, with excellent selectivity and high sensitivity.