OICC Press Journal of Nanostructure in Chemistry 2193-8865 4 3 (September 2014) 2014 07 24 Visual sensing of Hg2+ using unmodified Au@Ag core–shell nanoparticles 10.1007/s40097-014-0117-y EN Lihua Li Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, CN Department of Pharmacy, Wannan Medical College, Wuhu, 241002, CN Dexiang Feng Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, CN Department of Pharmacy, Wannan Medical College, Wuhu, 241002, CN Xian Fang Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, CN Xiaowei Han Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, CN Yuzhong Zhang Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, 241000, CN Journal Article 2014 07 24 Abstract In this work, we have developed a novel visual Hg 2+ sensor in aqueous solution using unmodified Au@Ag core–shell nanoparticles at room temperature, based on a redox reaction between Ag-shell and Hg 2+ . The prepared Au@Ag core–shell nanoparticles exhibited good monodispersity. In the presence of Hg 2+ , Hg 2+ was reduced into Hg (0) by Ag-shell, and deposited on the surface of Au-core to form Au–Hg alloys and caused nanoparticles aggregation, leading to the color changes of the solution from yellow to purplish red, and the surface plasmon resonance spectra of Au@Ag core–shell nanoparticles red shift. Under the optimal conditions, the visual sensor could selectively detect Hg 2+ as low as 0.4 µM with the naked eye and 5.0 nM by UV–vis spectra analysis methods. The designed sensor had several advantages: (1) the nanoparticles surface need not be functionalized. (2) The color change of the solution was in 2 s and could easily be observed with naked eyes. The visual sensor had been applied to detection of Hg 2+ in tap and lake water, which obtained satisfied result.