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Graphical abstract Highlights • Surface vibrational spectroscopies, PM-IRRAS and SERS, give direct insight into anion binding by self-assembled monolayers. • Three surface-attached, charge neutral diamidocarbazoles were demonstrated to act as sulphate anion receptors. • The relative sulphate binding affinities of the metal-supported receptors were estimated from the PM-IRRAS studies. • Partial hydrolysis of the amide bonds in the surface-attached receptors was observed in aqueous solutions. Abstract In this paper we demonstrate the applicability of surface vibrational spectroscopy techniques in sensing sulphate anions, using self-assembled monolayers of hydrogen bonding receptors. Three uncharged, diamidocarbazole receptors were synthesised and attached to gold and silver surfaces via one or two disulphide arms. Their ability to bind anions on the metal surfaces was investigated with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and surface enhanced Raman scattering (SERS) spectroscopy. Contrary to other techniques applied in optical sensors, such as UV–vis absorption, fluorescence or surface plasmon resonance, surface vibrational spectroscopy techniques used in this work not only display spectral changes proportional to the concentration of sulphate, but also provide an insight into the state of the receptor monolayer and its interactions with the analyte. While SERS measurements confirm the formation of anion-receptor complexes on metal surfaces, PM-IRRAS spectra were further employed to quantify the optical response of the sensor. The system can detect SO 4 2− anions within a concentration range of 10-6 – 10-1 M (in acetonitrile). An effect of the hydrogen bonds formed at the binding site of the diamidocarbazole molecules on the symmetry of sulphate anions is observed, which ultimately proves the anion-receptor binding. [ABSTRACT FROM AUTHOR]

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 Ca 2+ which is unmatched by analogous SERS sensors. We also prove simultaneous determination of calcium and magnesium in physiological concentrations with the nanosensor feasible. [ABSTRACT FROM AUTHOR]