title: Detection of mercury ions based on mercury-induced switching of enzyme-like activity of platinum/gold nanoparticles.
abstract: In this study, bimetallic platinum/gold nanoparticles (Pt/Au NPs) were found to exhibit peroxidase-like activity, and the deposition of mercury was found to switch the enzymatic activity to a catalase-like activity. Based on this phenomenon, we developed a new method for detecting mercury ions through their deposition on bimetallic Pt/Au NPs to switch the catalytic activity of Pt/Au NPs. Pt/Au NPs could be easily prepared through reduction of Au(3+) and Pt(4+) by sodium citrate in a one-pot synthesis. The peroxidase catalytic activity of the Pt/Au NPs was controlled by varying the ratios of Pt to Au. The Pt(0.1)/Au NPs (prepared with a [Au(3+)]/[Pt(4+)] molar ratio of 9.0/1.0) showed excellent oxidation catalysis for H(2)O(2)-mediated oxidation of Amplex® Red (AR) to resorufin. The oxidized product of AR, resorufin, fluoresces more strongly (excitation/emission wavelength maxima ca. 570/585 nm) than AR alone. The peroxidase catalytic activity of Pt(0.1)/Au NPs was switched to catalase-like activity in the presence of mercury ions in a 5.0 mM tris(hydroxymethyl)aminomethane (Tris)-borate solution (pH 7.0) through the deposition of Hg on the particle surfaces owing to the strong Hg-Au metallic bond. The catalytic activity of Hg-Pt(0.1)/Au NPs is superior (by at least 5-fold) to that of natural catalase (from bovine liver). Under optimal solution conditions [5.0 mM Tris-borate (pH 7.0), H(2)O(2) (50 mM), and AR (10 μM)] and in the presence of the masking agents polyacrylic acid and tellurium nanowires, the Pt(0.1)/Au NPs allowed the selective detection of inorganic mercury (Hg(2+)) and methylmercury ions (MeHg(+)) at concentrations as low as several nanomolar. This simple, fast, and cost-effective system enabled selective determination of the spiked concentrations of Hg(2+) and MeHg(+) in tap, pond, and stream waters.
authors.affiliation: Institute of Bioscience and Biotechnology, Center of Excellence for Marine Bioenvironment and Biotechnology, National Taiwan Ocean University, 2, Pei-Ning Road, Keelung, 20224, Taiwan.
authors.forename: Chao-Wei
authors.initials: CW
authors.lastname: Tseng
authors.forename: Hsiang-Yu
authors.initials: HY
authors.lastname: Chang
authors.forename: Jia-Yaw
authors.initials: JY
authors.lastname: Chang
authors.forename: Chih-Ching
authors.initials: CC
authors.lastname: Huang
mesh_terms: D002374:Catalase / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D005456:Fluorescent Dyes / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008628:Mercury / Q000032:analysis*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008767:Methylmercury Compounds / Q000032:analysis; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry / Q000378:metabolism; D010984:Platinum / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D007477:Ions; D008767:Methylmercury Compounds; D010545:Peroxides; D010984:Platinum; D006046:Gold; D006861:Hydrogen Peroxide; D002374:Catalase; D008628:Mercury