Agata Królikowska

SERS studies on the structure of thioglycolic acid monolayers on silver and gold

Chemisorption of thioglycolic acid (TGA) on silver and gold has been studied using surface-enhanced Raman scattering. We found that the strength of TGA strongly decreased after adsorption. Significantly more decreased strength was observed for TGA adsorbed on Au. The average conformation of adsorbed TGA molecules depends on the kind of the substrate and on degree of dissociation of TGA. The higher portion of TGA molecules adopts trans conformation when layers are formed on the Ag substrate and when more carboxylic acid groups are deprotonated. The ratio of gauche to trans conformers of TGA molecules significantly changed during the incubation on silver. In the first stage of incubation the relative amount of a gauche conformer increases, but after about 1 h the gauche conformer starts to disappear. The average conformation of TGA adsorbed on the gold substrate did not change during the incubation.

Construction of DNA biosensor at glassy carbon surface modified with 4-aminoethylbenzenediazonium salt

A simple, label-free electrochemical impedance-spectroscopy method for sequence-specific detection of DNA using a 4-aminoethylbenzenediazonium (AEBD) salt as a binder for amino-modified probe DNA is reported. This novel method simplifies the anchoring of DNA at the GC surface and opens new ways for the detection of hybridization. The hybridization of target DNA, without and with mismatches, with the probe DNA anchored at the GC surface modified with AEBD, greatly increases the interfacial electron transfer resistance at the double-stranded DNA modified electrodes for the redox couple Fe(CN)(6)(3-/4-). The resistance was measured using electrochemical impedance spectroscopy. The sensor response increased linearly with logarithm of concentration of target DNA in the range 2×10(-12)÷2×10(-6) M. The obtained quantification limit was circa 6.5×10(-17) mole in a 7 μL droplet and corresponded to a concentration of 9.2×10(-12) M of target DNA in the sample. This limit is equivalent to the detection of circa 4×10(7) copies of DNA in a 7 μL droplet or circa 5.7×10(12) DNA copies in one litre of sample.

Comparative Studies on IR, Raman, and Surface Enhanced Raman Scattering Spectroscopy of Dipeptides Containing ΔAla and ΔPhe

Three dipeptides containing dehydroresidues (ΔAla, Δ((Z))Phe, and Δ((E))Phe) were examined by IR, Raman, and surface-enhanced Raman techniques for the first time. The effect of the size and isomer type of the β-substituent in the dehydroresidue on the conformational structure of the peptide was evaluated by using the analysis of IR and Raman bands. Additionally, SERS spectroscopy provided insight into the adsorption mechanism of these species on the metal surface. SERS spectra were recorded at alkaline pH on the silver sol using visible light excitation. The dehydroresidues studied here strongly influenced the SERS profile of the peptides. The most pronounced SERS signal for all dipeptides was assigned to the symmetric stretching vibration of the carboxylate ions. This indicates that the dehydropeptides studied here primarily adsorb via the deprotonated carboxylic group. Additionally, the enhanced SERS bands in the range 1550-1650 cm(-1) show differences in contribution of the dehydroresidue to the adsorption mechanism of the studied peptides.

Exchange of Methyl‐ and Azobenzene‐Terminated Alkanethiols on Polycrystalline Gold Studied by Tip‐Enhanced Raman Mapping

Mixed thiol self-assembled monolayers (SAMs) presenting methyl and azobenzene head groups were prepared by chemical substitution from the original single-component n-decanethiol or [4-(phenylazo)phenoxy]hexane-1-thiol SAMs on polycrystalline gold substrates. Static contact-angle measurements were carried out to confirm a change in the hydrophobicity of the functionalized surfaces following the exchange reaction. The mixed SAMs presented contact-angle values between those of the more hydrophobic n-decanethiol and the more hydrophilic [4-(phenylazo)phenoxy]hexane-1-thiol single-component SAMs. By means of tip-enhanced Raman spectroscopy (TERS) mapping experiments, it was possible to highlight that molecular replacement takes place easily and first at grain boundaries: for two different mixed SAM compositions, TERS point-by-point maps with <50 nm step sizes showed different spectral signatures in correspondence to the grain boundaries. An example of the substitution extending beyond grain boundaries and affecting flat areas of the gold surface is also shown.

Nanoporous WO3–Fe2O3 films; structural and photo-electrochemical characterization

We investigated the structure and photo-electrochemical properties for water splitting of tungsten trioxide-ferric oxide thin films formed by spray pyrolysis. While annealing at 600°C produces films consisting of a mixture of monoclinic WO3 and hematite α-Fe2O3, the heating at a temperature above 1000°C affords formation of ferric tungstate Fe2WO6. Both kinds of films exhibit optical absorption range comparable or exceeding that of α-Fe2O3. Another important feature is a decreased rate of charge recombination of the mixed-oxide Fe2O3-WO3 with respect to the ferric oxide photo-anodes.

pH and Substrate Effect on Adsorption of Peptides Containing Z and E Dehydrophenylalanine. Surface-Enhanced Raman Spectroscopy Studies on Ag Nanocolloids and Electrodes

The silver substrates and pH dependent surface-enhanced Raman scattering (SERS) spectra of unsaturated derivatives of di- and tripeptides (dehydropeptides) are investigated. Experimental spectra were interpreted with the help of DFT calculations and normal-mode analysis. We choose as objects of our studies modified but natural peptides containing Z or E dehydrophenylalanine (((Z)/(E))ΔPhe) residue to study an effect of the type of the isomer on the interaction between the peptide and silver surfaces in the form of nanocolloidal particles and an electrochemically roughened electrode. We also observed that the SERS profile is sensitive to both the type of the studied SERS active substrate and pH, especially for the adsorption on the silver colloid. In general, all dehydropeptides interact with both SERS substrates upon deprotonation of the C-end of the molecule. The participation of the other fragments of the adsorbates such as the N-terminal amino group and the dehydroresidue is also manifested in the SERS spectra. Their orientation with respect to the silver surfaces is discussed in detail.

Fungal Ferromanganese Mineralisation in Cretaceous Dinosaur Bones from the Gobi Desert, Mongolia.

Well-preserved mycelia of fungal- or saprolegnia-like biota mineralised by ferromanganese oxides were found for the first time in long bones of Late Cretaceous dinosaurs from the Gobi Desert (Nemegt Valley, Mongolia). The mycelia formed a biofilm on the wall of the bone marrow cavity and penetrated the osteon channels of the nearby bone tissue. Optical microscopy, Raman, SEM/EDS, SEM/BSE, electron microprobe and cathodoluminescence analyses revealed that the mineralisation of the mycelia proceeded in two stages. The first stage was early post-mortem mineralisation of the hyphae by Fe/Mn-oxide coatings and microconcretions. Probably this proceeded in a mildly acidic to circumneutral environment, predominantly due to heterotrophic bacteria degrading the mycelial necromass and liberating Fe and Mn sorbed by the mycelia during its lifetime. The second stage of mineralisation, which proceeded much later following the final burial of the bones in an alkaline environment, resulted from the massive precipitation of calcite and occasionally barite on the iron/manganese-oxide-coated mycelia. The mineral phases produced by fungal biofilms colonising the interiors of decaying dinosaur bones not only enhance the preservation (fossilisation) of fungal remains but can also be used as indicators of the geochemistry of the dinosaur burial sites.