Abstract: During the last decades, much attention has been paid to trace detection of polycyclic aromatic hydrocarbons (PAHs) in water, because they are known to be toxic to biota and may bioaccumulate in aquatic organisms. Furthermore, PAH molecules are dissolved in water with extremely low concentrations because of their high octanol/water coefficients. Hence, for PAH detection a molecule specific technique that is capable to measure small concentrations is necessary. Raman scattering is a vibrational spectroscopic technique that allows specific substance identification due to its inherent molecule fingerprinting capability, by detecting the inelastically scattered laser light from molecules. However, conventional Raman spectroscopy has the drawback of very small cross sections and usually a broad and strong fluorescence based background, both limiting trace analysis of chemicals. To overcome the first drawback, surface enhanced Raman spectroscopy (SERS) has successfully been used. SERS is a powerful analytical tool that is based on Raman signal amplification of analytes by the local field of noble metal nanostructures excited with laser light. To remove the fluorescence background shifted excitation Raman difference spectroscopy (SERDS) has been invented.
In this presentation a general introduction in the techniques of SERS and SERDS as well as in the unique optical properties of noble metal nanoparticles will be given, followed by an explanation of the preparation of the nanoparticle ensembles, which serve as SERS substrates. Afterwards I will demonstrate that combining SERS with SERDS allows trace detection of pollutant chemicals. I will show how crucial the Raman signal of pyrene depends on the morphology of the nanoparticles and demonstrate that the Raman intensity is maximized if optimised nanoparticles are used. For this purpose, we have determined the limit of detection (LOD) for pyrene and fluoranthene in aqueous solution by applying SERS in combination with SERDS, using different morphologies of the SERS substrates. With an optimised SERS substrate the LOD of pyrene and fluranthene has been determined to be as low as 2 nmol/L (figure 1.), which is sufficient for trace analysis. Finally, I show the Raman response as a function of time. Since response times clearly below 10 minutes are observed, the system is capable to be implemented in an alarm sensor that can detect traces of PAHs in water in a short time.

[1] Y.-H. Kwon, R. Ossig, F. Hubenthal, H.-D. Kronfeldt, J. Raman. Spec., DOI 10.1002/jrs.4093
[2] F. Hubenthal, D. Blázquez Sánchez, N. Borg, H. Schmidt, H.-D. Kronfeldt, F. Träger; Appl. Phys. B 95, 351 (2009)

Brief Biography of the Speaker:
Frank Hubenthal finished his PhD work in 2001 at the University of Kassel and received his Habilitation in 2007. In the same year he was awarded as associated professor. Frank Hubenthal is a member of the Center for Interdisciplinary Nanostructure Science and Technology – CINSaT at the University of Kassel, a member of the American Nano Society and the German Physics Society. His research concentrates on the production, characterisation and application of noble metal nanoparticles. In particular, his interest is to exploit the local near fields of noble metal nanoparticles for surface enhanced Raman spectroscopy and surface structuring. Furthermore, Frank Hubenthal investigates the ultrafast electron dynamics and determines the dephasing times of localized surface plasmon resonances and the damping parameters of noble metal nanoparticles. By quantifying the different damping contributions to the dephasing time, he contributes to the fundamental understanding of the plasmons nature. Frank Hubenthal has written more than 45 publications and contributed to the major reference work Comprehensive Nanoscience and Technology Eds.: Andrews DL, Scholes, GD and Wiederrecht GP, Oxford: Academic Press.