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

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 mu M by eye and 0.1 mu M by UV-Vis spectroscopy. The LOD by eye is lower than the lowest previously reported value (4.0 mu M). There is a good linear relationship between A/A(0) and the concentration of NO2- from 1.0 to 20.0 mu M 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.