Virginia Merk

Identification of aqueous pollen extracts using surface enhanced Raman scattering (SERS) and pattern recognition methods

Aqueous pollen extracts of varying taxonomic relations were analyzed with surface enhanced Raman scattering (SERS) by using gold nanoparticles in aqueous suspensions as SERS substrate. This enables a selective vibrational characterization of the pollen water soluble fraction (mostly cellular components) devoid of the spectral contributions from the insoluble sporopollenin outer layer. The spectra of the pollen extracts are species-specific, and the chemical fingerprints can be exploited to achieve a classification that can distinguish between different species of the same genus. In the simple experimental procedure, several thousands of spectra per species are generated. Using an artificial neural network (ANN), it is demonstrated that analysis of the intrinsic biochemical information of the pollen cells in the SERS data enables the identification of pollen from different plant species at high accuracy. The ANN extracts the taxonomically-relevant information from the data in spite of high intra-species spectral variation caused by signal fluctuations and preparation specifics. The results show that SERS can be used for the reliable characterization and identification of pollen samples. They have implications for improved investigation of pollen physiology and for allergy warning.

Porous MgF2-over-gold nanoparticles (MON) as plasmonic substrate for analytical applications

Porous MgF2-over-nanoparticles (MON) surfaces are fabricated from immobilized gold nanoparticles of different sizes on a glass surface by coating them with a magnesium fluoride layer. High mechanical stability of the resulting plasmonic surface is obtained, and optical spectroscopy across a very wide optical window is enabled. The nanoscopic characterization by scanning force microscopy and electron microscopy shows a uniform assembly of the gold nanoparticles in monolayers and a complete coating by magnesium fluoride. Surface-enhanced Raman scattering (SERS) experiments provide evidence that organic analyte molecules have free access to the gold surface, and interact with the immobilized nanoparticles in a very similar fashion as with uncoated surfaces. As the spectroscopic results indicate, the coating leads to properties that are favourable for plasmonic enhancement of optical processes excited in the visible and near-infrared. As demonstrated by experiments using SERS, as well as by finite difference time domain (3D-FDTD) simulations, enhancement factors are obtained that allow for analytical applications with optical excitations ranging from the visible to the near infrared.

Optical properties of silver nanocube surfaces obtained by silane immobilization

Abstract Silver nanocubes were synthesized by the polyol method and immobilized on a surface in a simple approach using an aminopropyltriethoxysilane (APTES). The optical and structural properties of the polyvinylpyrrolidone (PVP) stabilized nanocubes were investigated in solution and on glass surfaces. The SERS enhancement factors at two excitation wavelengths for crystal violet were compared with electric fields arising in different nano¬particle configurations using finite-difference time-domain simulations. They are in agreement with the preferred face-to-face orientation in the nanoaggregates on the surfaces. The facile immobilization enables on-demand preparation and use of the nanocubes in real analytical applications.