8 research outputs found
Microanalysis of Organic Pigments in Ancient Textiles by Surface-Enhanced Raman Scattering on Agar Gel Matrices
We review some new methods based on surface-enhanced Raman scattering (SERS) for the nondestructive/minimally invasive identification of organic colorants in objects whose value or function precludes sampling, such as historic and archeological textiles, paintings, and drawing. We discuss in detail the methodology we developed for the selective extraction and identification of anthraquinones and indigoids in the typical concentration used in textiles by means of an ecocompatible homogeneous nanostructured agar matrix. The extraction system was modulated according to the chemical properties of the target analyte by choosing appropriate reagents for the extraction and optimizing the extraction time. The system has been found to be extremely stable, easy to use and produce, easy to store, and at the same time able to be analyzed even after long time intervals, maintaining its enhancement properties unaltered, without the detriment of the extracted compound. Highly structured SERS band intensities have been obtained from the extracted dyes adopting laser light excitations at 514.5 and 785 nm of a micro-Raman setup. This analytical method has been found to be extremely safe for the analyzed substrates, thus being a promising procedure for the selective analysis and detection of molecules at low concentration in the field of artworks conservation
Graphene Oxide/Silver Nanoparticles Platforms for the Detection and Discrimination of Native and Fibrillar Lysozyme: A Combined QCM and SERS Approach
We propose a sensing platform based on graphene oxide/silver nanoparticles arrays (GO/AgNPs) for the detection and discrimination of the native and toxic fibrillar forms of an amyloid-prone protein, lysozyme, by means of a combination of Quartz Crystal Microbalance (QCM) and Surface Enhanced Raman Scattering (SERS) measurements. The GO/AgNPs layer system was obtained by Langmuir-Blodgett assembly of the silver nanoparticles followed by controlled adsorption of GO sheets on the AgNPs array. The adsorption of native and fibrillar lysozyme was followed by means of QCM, the measurements provided the kinetics and the mechanism of adsorption as a function of protein concentration as well as the mass and thickness of the adsorbed protein on both nanoplatforms. The morphology of the protein layer was characterized by Confocal Laser Scanning Microscopy experiments on Thioflavine T-stained samples. SERS experiments performed on arrays of bare AgNPs and of GO coated AgNP after native, or fibrillar, lysozyme adsorption allowed for the discrimination of the native form and toxic fibrillar structure of lysozyme. Results from combined QCM/SERS studies indicate a general construction paradigm for an efficient sensing platform with high selectivity and low detection limit for native and amyloid lysozyme
Resonance Raman Spectra of o‑Safranin Dye, Free and Adsorbed on Silver Nanoparticles: Experiment and Density Functional Theory Calculation
The
properties of o-Safranin (SO) dye in the first electronic excited
state were studied with combined experimental and theoretical methods.
The electronic absorption spectra of SO molecules are measured in
water solution and in the presence of silver nanoparticles. The normal
Raman (NRS) and resonance Raman (RR) spectra of solid SO and the surface
enhanced Raman (SERS) and surface enhanced resonance Raman (SEÂ[R]ÂRS)
spectra of SO adsorbed on silver nanoparticles are measured at different
excitation energies. The enhancement factors for selected vibrational
bands of the RR, SERS, and SEÂ[R]ÂRS spectra of SO have been obtained
with respect to the NRS spectra of the solid after a careful evaluation
of the experimental conditions. The data furnished useful information
on the excited electronic states and the interactions of SO with silver
nanoparticles. The experimental results are discussed on the basis
of DFT and TD-DFT calculations (B3LYP/6-311+GÂ(d,p)) on the isolated
SO molecule
SERS Spectra of Alizarin Anion–Ag<sub><i>n</i></sub> (<i>n</i> = 2, 4, 14) Systems: TDDFT Calculation and Comparison with Experiment
Using density functional theory (DFT)
and various cluster models for the simulation of the interaction between
alizarin and silver nanoparticles, we calculated the SERS spectra
of the AZ anion–Ag<sub><i>n</i></sub> (<i>n</i> = 2, 4, 14) complexes and compared the results with experiment.
The analysis of the calculated SERS spectra helped distinguishing
the contribution of the chemical and electromagnetic mechanisms to
the spectral enhancement, under the assumption that the excitation
energies of the clusters are comparable with the local plasmon energies
of nanoparticles. The results show a certain dependence of the relative
Raman intensities and peak positions on the silver cluster size. Calculation
of UV–vis transition energies and Raman spectra of the complexes
have been performed under the assumption that the AZ anion is bounded
to the silver clusters through the oxygen atoms of the Cî—»O
groups in 1,9 positions, in a edge-on perpendicular orientation. The
calculated SERS spectra show an acceptable similarity with the experimental
SERS spectra carried out with excitation at 632 nm. The results of
the calculation under preresonance condition with respect to chromophore
located and cluster located excitations are compatible with mechanisms
of enhancement acting on different parts of the AZ anion molecule.
The calculations were performed using the B3LYP hybrid density functional.
A 6-31gÂ(d) basis set for H, C, O, and LANL2DZ basis set for Ag were
used. Vertical excitation energies and the corresponding oscillator
strengths were calculated by means of time dependent density functional
theory (TDDFT)
Bioplastics on marine sandy shores: Effects on the key species Talitrus saltator (Montagu, 1808)
Talitrid amphipods are an important component of detritus web, playing a key role in the fragmentation of organic matters of marine and terrestrial origin, and it is well known that sandhoppers ingest microplastics. To assess the ef-fective consumption of bioplastics and their effects on survival rate and on pollutants transfer (i.e. phthalates) on supralittoral arthropods, laboratory experiments were conducted by feeding adult T. saltator with two different types of bioplastic commonly used in the production of shopping bags. Groups of about 20 individuals were fed with 10 x 10 cm sample sheets of the two types of bioplastic for four weeks. The results show that amphipods ingest bioplastics even in the absence of microbial film and that ingestion of bioplastic can have effects on talitrid amphipods. Microtomographic analyses of faecal pellets seem consistent with this finding. The high phthalate concentrations in freshly collected individuals suggest the presence in the environment of these compounds, and the ability of amphi-pods to assimilate them, while the decrease in phthalate concentrations in bioplastic-fed individuals could be attrib-uted to the scavenging effect of virgin plastic, as already observed in a previous study. In summary, the results indicate that different bioplastics may have effects on T. saltator (i.e. survival rate and faecal pellets structure) and con-firm a potential role of amphipods in the degradation of bioplastics in supralittoral zone of marine sandy beaches, even when bioplastics are not colonized by bacterial biofilm that seems to improve palatability
Study on the technique of the Roman age mural paintings by micro-XRF with Polycapillary Conic Collimator and micro-Raman analyses
XRF and micro-Raman stratigraphic microanalyses of fragments of some mural paintings, belonging to the Archaeological Site of Oplonti (Napoli) and the Vigna Barberini site in the Palatino (Roma), were performed. In order to collimate the fluorescence X-rays emitted by the samples, an X-ray polycapillary conic collimator (PCC) has been used in front of the detector. This device arrangement is compact, versatile, and portable. The nature of the pigments, the compositional elements, and the thickness of the fragment layers have been studied. The stratigraphic analysis partially confirms the preparation techniques described by Plinius and Vitruvius; moreover it confirms the hypothesis that the artifacts are not fresco paintings. This work has been conducted within the context of a wider research on the Roman age mural paintings. (c) 2005 Elsevier SAS. All rights reserved