||In this work, we develop a simple and selective sensing method for the detection of mercury ions based on surface plasmon resonance (SPR) spectrum change of Au-Ag core-shell triangular nanoplates. When the concentration of mercury is increased, the etching-induced change of particle size and shape also leads to the decrease of
the absorption peak at the fixed wavelength, until a spectrum dip takes place. This spectral change of “peak-todip” greatly enlarges the detection range of mercury ions, which could be fine tuned by changing the initial thickness of the Ag coating. Under optimal conditions, the decrease of the logarithmic absorption intensity has a good
linear response with the concentration of mercury ions increasing from 10 to 1000 μM, and the limit of detection
(LOD) is 0.88 μM. Interference studies and real samples test indicate that, this new sensing method has a good
selection for mercury ions and can be practically used in lake water. This work shows the surface etchinginduced SPR shift can also leads to the intensity change with “peak-to-dip” fashion, which greatly enlarge the
concentration range of the detection and could be widely applied in the spectroscopy sensing based on SPR.