The study demonstrates that a combination of plasmonic nanostructures and artificial receptors can be applied for sensing small molecular species. Gold nanoshells containing magnetic cores are used as the SERS-active substrates, which opens the way for the development of multimodal contrast agents with applicability extended to sensing or for the separation of analytes by magnetic solid-phase extraction. Disubstituted ureas forming hydrogen-bonded complexes with certain anions can be employed as molecular sensors. In this case study, gold nanoshells with silica-coated Mn-Zn ferrite cores were prepared by a multistep procedure. The nanoshells were co-functionalized with an N-(4-mercaptophenyl)-N'-(4-nitrophenyl)urea sensor synthesized directly on the gold surface, and with 4-nitrothiophenol, which is adopted as an internal standard. SERS measurements were carried out with acetonitrile solutions of tetrabutylammonium fluoride (Bu4NF) over a concentration range of 10-10-10-1 mol L-1. The spectral response of the sensor is dependent on the fluoride concentration in the range of 10-5-10-1 mol L-1. To investigate further the SERS mechanism, a model sensor, N-(4-bromophenyl)-N'-(4-nitrophenyl)urea, was synthesized and used in Raman spectroscopy with solutions of Bu4NF, up to a molar ratio of 1 : 20. The spectra and the interactions between the sensors and fluoride anions were also studied by extensive DFT computations.

Charles University Faculty of Mathematics and Physics 5 Holešovičkách 2 180 00 Praha 8 Czech Republic

Department of Analytical Chemistry University of Chemistry and Technology Prague Technická 5 166 28 Praha 6 Czech Republic

Department of Chemistry Johannes Gutenberg University Mainz Duesbergweg 10 14 D 55128 Mainz Germany

Fachbereich Chemie TU Kaiserslautern Erwin Schrödinger Str 54 67663 Kaiserslautern Germany

Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences Flemingovo náměstí 542 2 160 00 Praha 6 Czech Republic

Institute of Physics of the Czech Academy of Sciences Cukrovarnická 10 112 162 00 Praha 6 Czech Republic

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