2-Mercaptoethanesulfonate (MES) anion-functionalized silver nanoparticles as an efficient SERS-based sensor of metal cations

The first SERS (surface enhanced Raman scattering) sensor for detection of alkaline and alkaline earth metal cations is presented. System composed of silver nanoparticles functionalized with 2-mercaptoethanesulfonate (MES) anions exhibits high selectivity and sensitivity toward aforementioned cations thanks to high affinity of surface-attached MES monolayer to cations. This interaction results in formation of contact-ion pairs between MES sulfonate groups and metal cations. We demonstrate a big potential of the Ag nanoparticles functionalized with MES in quantitative detection of a great variety of cations, including alkaline and alkaline earth metal cations, down to 10−8 M in case of Ca2+ which is unmatched by analogous SERS sensors. We also prove simultaneous determination of calcium and magnesium in physiological concentrations with the nanosensor feasible.