Ratiometry, Wavelength, and Intensity: Triple Signal Readout for Colorimetric Sensing of Mercury Ions by Plasmonic Cu_2-xSe Nanoparticles

Abstract

In this study, we have reported a new colorimetric platform for sensitive and selective sensing of Hg2+ using near-infrared (NIR) plasmonic Cu2-xSe nanoparticles (NPs) as reporters. Because of ultrahigh affinity between Hg2+ and Se2–, the added Hg2+ can react with Cu2-xSe NPs and exchange their Cu+/Cu2+, yielding a HgSe layer around the host NPs. Accordingly, the absorption profiles of the Cu2-xSe NPs are modulated substantially: The absorbance at 400–600 nm is increased, and the NIR localized surface plasmon resonance dramatically decreases with a more than 150 nm bathochromic shift. Thus, the system possesses triple signal responses, namely, ratiometry, wavelength, and intensity, to the analytes simultaneously. Such uniquely multiple signal output not only provides more choices for the quantification, but also enhances the reliability in the analyte detection. By rationally choosing poly(allylamine hydrochloride) as the NP template, Hg2+ ions can be determined as ranging from 0–800 nM. The detection limit is as low as 2.7 nM, which is nearly 4 times lower than the limit value (10 nM) defined by the U.S. Environmental Protection Agency for drinking water. Other heavy/transition metal ions, such as Cu2+, Ag+, Pb2+, Cd2+, Ni2+, Co2+, Mn2+, Zn2+, Cr3+, Fe2+, and FeF63–, do not interfere with the sensing. Especially, Hg2+ contents can be quantified, even if their concentrations are as low 10 nM in tap water and common environmental water samples. Due to favorable analytical performance, the proposed Cu2-xSe NPs based system has potential applications in monitoring trace Hg2+ in various real samples, even in drinking water.