title: Chemical speciation of heavy metals by surface-enhanced Raman scattering spectroscopy: identification and quantification of inorganic- and methyl-mercury in water.
abstract: Chemical speciation of heavy metals has become extremely important in environmental and analytical research because of the strong dependence that toxicity, environmental mobility, persistence and bioavailability of these pollutants have on their specific chemical forms. Novel nano-optical-based detection strategies, capable of overcoming the intrinsic limitations of well-established analytic methods for the quantification of total metal ion content, have been reported, but the speciation of different chemical forms has not yet been achieved. Here, we report the first example of a SERS-based sensor for chemical speciation of toxic metal ions in water at trace levels. Specifically, the inorganic Hg(2+) and the more toxicologically relevant methylmercury (CH₃Hg(+)) are selected as analytical targets. The sensing platform consists of a self-assembled monolayer of 4-mercaptopyridine (MPY) on highly SERS-active and robust hybrid plasmonic materials formed by a dense layer of interacting gold nanoparticles anchored onto polystyrene microbeads. The co-ordination of Hg(2+) and CH₃Hg(+) to the nitrogen atom of the MPY ring yields characteristic changes in the vibrational SERS spectra of the organic chemoreceptor that can be qualitatively and quantitatively correlated to the presence of the two different mercury forms.
authors.affiliation: Departamento de Química Física e Inorgánica, Universitat Rovira i Virgili, Avda. Països Catalans 26, 43007 Tarragona, Spain. luca.guerrini@ctqc.org ramon.alvarez@urv.cat.
authors.forename: Luca
authors.initials: L
authors.lastname: Guerrini
authors.forename: Ignacio
authors.initials: I
authors.lastname: Rodriguez-Loureiro
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Correa-Duarte
authors.forename: Yih Hong
authors.initials: YH
authors.lastname: Lee
authors.forename: Xing Yi
authors.initials: XY
authors.lastname: Ling
authors.forename: F Javier
authors.initials: FJ
authors.lastname: García de Abajo
authors.forename: Ramon A
authors.initials: RA
authors.lastname: Alvarez-Puebla
mesh_terms: D006046:Gold / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008628:Mercury / Q000032:analysis*; D053768:Metal Nanoparticles / Q000737:chemistry; D008767:Methylmercury Compounds / Q000032:analysis*; D011137:Polystyrenes / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D007477:Ions; D008767:Methylmercury Compounds; D011137:Polystyrenes; D011725:Pyridines; D014874:Water Pollutants, Chemical; C042861:4-thiopyridine; D006046:Gold; D008628:Mercury