Core/shell nanofiber characterization by Raman scanning microscopy

Core/shell nanofibers are becoming increasingly popular for applications in tissue engineering. Nanofibers alone provide surface topography and increased surface area that promote cellular attachment; however, core/shell nanofibers provide the versatility of incorporating two materials with different properties into one. Such synthetic materials can provide the mechanical and degradation properties required to make a construct that mimics in vivo tissue. Many variations of these fibers can be produced. The challenge lies in the ability to characterize and quantify these nanofibers post fabrication. We developed a non-invasive method for the composition characterization and quantification at the nanoscale level of fibers using Confocal Raman microscopy. The biodegradable/biocompatible nanofibers, Poly (glycerol-sebacate)/Poly (lactic-co-glycolic) (PGS/PLGA), were characterized as a part of a fiber scaffold to quickly and efficiently analyze the quality of the substrate used for tissue engineering

A Chronoamperometric Kinetic Study of the Reduction of the Double Fe\u3csub\u3e4\u3c/sub\u3eS\u3csub\u3e4\u3c/sub\u3e Clustered Ferredoxin of Clostridium Pasteurianum by Methylviologen

In advancing our earlier work on single cluster redox proteins, we report here a chronoamperometric kinetic study of the homogeneous reduction of Clostridium pasteurianum ferredoxin (n = 2, U°7.6 = −395 mV versus n.h.e.) by methylviologen (U°7.0 = −420 mV). This ferredoxin has two Fe4S4* (S* = inorganic sulfide) clusters each of which has n = 1 and can be formally represented as 8 Fe0,0, 8 Fe0,r and 8 Fer,r′ This ferredoxin is similar to P. aerogenes ferredoxin for which the X-ray crystallographic structure shows that the two clusters are about 1.2 nm apart. Rates were determined at two temperatures. Using computer simulation of the catalytic mechanism with two homogeneous electron transfer steps, it was found that both electrons are transferred at equal rates, with k25°C = 4.7×105 M−1 s−1 and k15°C = 1.5 × 105M−1 s−1. Since k1 = k2 at both temperatures it is concluded that under these reducing conditions, where 8 Fe0,r does not come to equilibrium with other species during the reduction process, the two clusters operate independently of each other

Evaluating Molecular Evolution of Kerogen by Raman Spectroscopy: Correlation with Optical Microscopy and Rock-Eval Pyrolysis

Vitrinite maturity and programmed pyrolysis are conventional methods to evaluate organic matter (OM) regarding its thermal maturity. Moreover, vitrinite reflectance analysis can be difficult if prepared samples have no primary vitrinite or dispersed widely. Raman spectroscopy is a nondestructive method that has been used in the last decade for maturity evaluation of organic matter by detecting structural transformations, however, it might suffer from fluorescence background in low mature samples. In this study, four samples of different maturities from both shale formations of Bakken (the upper and lower members) Formation were collected and analyzed with Rock-Eval (RE) and Raman spectroscopy. In the next step, portions of the same samples were then used for the isolation of kerogen and analyzed by Raman spectroscopy. Results showed that Raman spectroscopy, by detecting structural information of OM, could reflect thermal maturity parameters that were derived from programmed pyrolysis. Moreover, isolating kerogen will reduce the background noise (fluorescence) in the samples dramatically and yield a better spectrum. The study showed that thermal properties of OM could be precisely reflected in Raman signals

Templated photonic crystal fabrication of stoichiometrically complex nanoparticles for resonance raman solid cross section determinations

Development of methods to fabricate nanoparticles is of great interest for many applications. In this paper, we developed a facile method to fabricate complex stoichiometrically defined nanoparticles by ultilizing the defined volume interstices of close-packed photonic crystals. Fabrication of small defined size nanoparticles enables measurements of resonance Raman cross sections of solid materials. We successfully ultilized this method to fabricate mixed NaNO3/Na2SO4 nanoparticles with a defined stoichiometry on the surface of the photonic crystal spherical particles. We used these stoichiometrically defined NaNO3/Na2SO 4 nanoparticles to determine the solid UV resonance Raman cross section of the NO31 symmetric stretching band (229 nm excitation wavelength) by monitoring the Raman spectrum of Na2SO4 as an internal standard. These are the first resonance Raman cross section measurements of solids that avoid the biasing of self-absorption. These NaNO3/Na2SO4 nanoparticles appear to show a more facile photolysis than is observed for normal solid NaNO3 samples. This templated photonic crystal fabrication of complex nanoparticle method will be important for many applications. © 2011 American Chemical Society