4 research outputs found
Surface-Enhanced Raman Spectroscopy of Acetil-neuraminic Acid on Silver Nanoparticles: Role of the Passivating Agent on the Adsorption Efficiency and Amplification of the Raman Signal
We present a combined
experimental and theoretical study dedicated
to analyzing the surface-enhanced Raman spectra of solutions of citrate-covered
silver nanoparticles (NPs) in the presence of acetil-neuraminic acid
(Neu5Ac). The Raman signals from Neu5Ac (particularly the bands located
at 1002 and 1237 cm<sup>â1</sup>) can easily be detected for
concentrations as low as 1 mg/dl, providing outstanding molecular
sensing properties for our synthesized Ag-NPs. When compared to its
solid phase, Neu5Ac adsorption on citrate-covered Ag particles leads
to enhanced Raman intensities; many vibrational frequencies are shifted;
and relative intensities undergo significant changes. These variations
in the spectra complicate molecular identification, especially in
mixed overlayers as the ones considered in this work. Consequently,
experimental results are discussed on the basis of extensive density
functional theory (DFT) calculations on model citrate-covered silver
clusters with coadsorbed Neu5Ac species. Several citrateâNeu5Ac-cluster
complexes are optimized, and the Raman spectra of every stable structure
are calculated. The theoretical data reveal a complex interplay between
the chemical nature and distribution of the adsorbates. Citrate molecules
prefer to aggregate on the silver surface, leaving thus sizable regions
of the Ag cluster exposed for Neu5Ac adsorption. The simulated Raman
spectra of citrateâNeu5AcAg complexes show acceptable similarities
with experimental SERS measurements, allowing for a clear identification
of the different vibrational bands. By changing the functional groups
attached to the Ag cluster it is possible to modulate the adsorption
properties and Raman response of Neu5Ac. DFT calculations reveal that
propanethiol adsorption on model Ag clusters allows the formation
of a more uniform molecular overlayer, effectively protecting the
silver surface from the surrounding media. We predict that Ag-NPs
functionalized with propanethiol species are not efficient substrates
for Raman detection of Neu5Ac. The previous predictions are corroborated
by performing SERS measurements on propanethiol-covered Ag-NPs exposed
to different concentrations of Neu5Ac from which the absence of Neu5Ac
spectral features is observed. The here-used DFT scheme provides an
adequate theoretical frame to predict and understand the physical
origin of the Raman response of adsorbed molecules in Ag-NPs, and
we expect that this predictability may extend to other metallic NPs
Multielemental analysis and classification of amaranth seeds according to their botanical origin
The characterization of amaranth seeds (Amaranthus spp.) was developed for Amaranthus hypochondriacus, Amaranthus cruentus, and Amaranthus dubius. The elemental concentrations were determined by inductively coupled plasma optic atomic spectroscopy. Pattern recognition methods were used for the characterization of seed samples: nonsupervised methods included principal components analysis and cluster analysis; supervised methods were linear discriminant analysis and partial least squares discriminant analysis (PLS-DA). Informed are the concentrations of the following elements: Ag, Al, Ba, Ca, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, S, Sr, V, Zn, and Zr. The lowest mineral content was found in A. hypochondriacus, and the highest one was found in A. dubius. For the classification, selected variables for all multivariate methods were Ba, Cr, Li, Mn, Ni, S, and Sr. Nonsupervised methods allowed us to distinguish between the three species of amaranth; however, PLS-DA supervised methods showed the best prediction ability.Fil: Aguilar, Elba Graciela. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; ArgentinaFil: Cantarelli, Miguel Angel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Luis. Instituto de QuĂmica de San Luis. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia. Instituto de QuĂmica de San Luis; Argentina. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Marchevsky, Eduardo Jorge. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Luis. Instituto de QuĂmica de San Luis. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia. Instituto de QuĂmica de San Luis; Argentina. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; ArgentinaFil: Escudero, Nora L.. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; ArgentinaFil: Camiña, JosĂ© Manuel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentin