Analysis of Automotive Paint Smears Using Attenuated Total Reflection Infrared Microscopy.

Paint smears represent a type of automotive paint sample found at a crime scene that is problematic for forensic automotive paint examiners to analyze as there are no reference materials present in automotive paint databases to generate hit-lists of potential suspect vehicles. Realistic paint smears are difficult to create in a laboratory and have also proven challenging to analyze because of the mixing of the various automotive paint layers. A procedure based on an impact tester has been developed to create smears to simulate paint transfer between vehicles during a collision. Data collected from 24 original equipment manufacturer (OEM) paints in simulated collisions using an impact tester with a steel (inert) substrate to simulate vehicle to vehicle collisions shows that attenuated total reflection infrared microscopy can isolate individual paint layers. For each OEM paint sample, the corresponding smear obtained was dependent upon the conditions used. By varying these conditions, the number of distinct layers obtained could be tuned for each of the OEM paints investigated. Furthermore, the IR spectrum of each layer extracted from the paint smear using alternating least squares was found to compare favorably to an in-house OEM paint infrared spectral library for each layer as the correct match (make and model of the vehicle from which the smear originated) was always found as a top five hit in the hit-list. The results of this study indicate that paint smears developed using an impactor can serve as the basis of realistic proficiency tests for forensic laboratories.

Single-photon oxidation of C60 by self-sensitized singlet oxygen.

C60 is regarded as the most efficient singlet oxygen (1O2) photosensitizer. Yet, its oxidation by self-sensitized 1O2 remains unclear. The literature hints both oxygen and C60 must be at excited states to react, implying a two-photon process: first, oxygen is photosensitized (1C60•1O2); second, C60 is photoexcited (1[Formula: see text]•1O2). However, this scheme is not plausible in a solvent, which would quench 1O2 rapidly before the second photon is absorbed. Here, we uncover a single-photon oxidation mechanism via self-sensitized 1O2 in solvents above an excitation energy of 3.7 eV. Using excitation spectroscopies and kinetics analysis, we deduce photoexcitation of a higher energy transient, 3[Formula: see text]•3O2, converting to 1[Formula: see text]•1O2. Such triplet-triplet annihilation, yielding two simultaneously-excited singlets, is unique. Additionally, rate constants derived from this study allow us to predict a C60 half-life of about a minute in the atmosphere, possibly explaining the scarceness of C60 in the environment.

Quantification of Thermal Oxidation in Metallic Glass Powder using Ultra-small Angle X-ray Scattering.

In this paper, the composition, structure, morphology and kinetics of evolution during isothermal oxidation of Fe48Cr15Mo14Y2C15B6 metallic glass powder in the supercooled region are investigated by an integrated ex-situ and in-situ characterization and modelling approach. Raman and X-ray diffraction spectra established that oxidation yielded a hierarchical structure across decreasing length scales. At larger scale, Fe2O3 grows as a uniform shell over the powder core. This shell, at smaller scale, consists of multiple grains. Ultra-small angle X-ray scattering intensity acquired during isothermal oxidation of the powder over a wide Q-range delineated direct quantification of oxidation behavior. The hierarchical structure was employed to construct a scattering model that was fitted to the measured intensity distributions to estimate the thickness of the oxide shell. The relative gain in mass during oxidation, computed theoretically from this model, relatively underestimated that measured in practice by a thermogravimetric analyzer due to the distribution in sizes of the particles. Overall, this paper presents the first direct quantification of oxidation in metallic glass powder by ultra-small angle X-ray scattering. It establishes novel experimental environments that can potentially unfold new paradigms of research into a wide spectrum of interfacial reactions in powder materials at elevated temperatures.

Electrochemical and Surface-Plasmon Correlation of a Serum-Autoantibody Immunoassay with Binding Insights: Graphenyl Surface versus Mercapto-Monolayer Surface.

We present here the correlation of picomolar affinities between surface-plasmon and electrochemical immunoassays for the binding of serum glutamic acid decarboxylase 65 autoantibody (GADA), a biomarker of type 1 diabetes (T1D), to its antigen GAD-65. Carboxylated (∼5.0%)-graphene-modified immunoassembly on a gold surface-plasmon chip or on an electrochemical array provided significantly larger binding affinity, higher sensitivity, and lower detection limits than a self-assembled monolayer surface of mercaptopropionic acid (MPA). Estimation of the relative surface -COOH groups by covalent tagging of an electroactive aminoferrocene showed that the graphenyl surface displayed a greater number of -COOH groups (9-fold) than the MPA surface. X-ray-photoelectron-spectroscopy analysis showed more C-O and C═O functionalities on the graphene-COOH surface than on the MPA surface. The graphene-COOH coating on gold exhibited ∼5.5-fold enhancement of plasmon signals compared with a similar coating on a plain glass surface. In summary, this article provides a quantitative comparison of carboxylated graphene with a mercapto-monolayer immunoassembly. Additionally, we propose that the binding-constant value can be useful as a quality-control checkpoint for reproducible and reliable production of large-scale biosensors for clinical bioassays.

Molecular and Biocompatibility Characterization of Red Blood Cell Membrane Targeted and Cell-Penetrating-Peptide-Modified Polymeric Nanoparticles.

Red blood cells (RBCs) express a variety of immunomodulatory markers that enable the body to recognize them as self. We have shown that RBC membrane glycophorin A (GPA) receptor can mediate membrane attachment of protein therapeutics. A critical knowledge gap is whether attaching drug-encapsulated nanoparticles (NPs) to GPA and modification with cell-penetrating peptide (CPP) will impact binding, oxygenation, and the induction of cellular stress. The objective of this study was to formulate copolymer-based NPs containing model fluorescent-tagged bovine serum albumin (BSA) with GPA-specific targeting ligands such as ERY1 (ENPs), single-chain variable antibody (scFv TER-119, SNPs), and low-molecular-weight protamine-based CPP (LNPs) and to determine their biocompatibility using a variety of complementary high-throughput in vitro assays. Experiments were conducted by coincubating NPs with RBCs at body temperature, and biocompatibility was evaluated by Raman spectroscopy, hemolysis, complement lysis, and oxidative stress assays. Data suggested that LNPs effectively targeted RBCs, conferring 2-fold greater uptake in RBCs compared to ENPs and SNPs. Raman spectroscopy results indicated no adverse effect of NP attachment or internalization on the oxygenation status of RBCs. Cellular stress markers such as glutathione, malondialdehyde, and catalase were within normal limits, and complement-mediated lysis due to NPs was negligible in RBCs. Under the conditions tested, our data demonstrates that molecular targeting of the RBC membrane is a feasible translational strategy for improving drug pharmacokinetics and that the proposed high-throughput assays can prescreen diverse NPs for preclinical and clinical biocompatibility.

Thermoset-cross-linked lignocellulose: a moldable plant biomass.

The present work demonstrates a high biomass content (i.e., up to 90% by weight) and moldable material by controlled covalent cross-linking of lignocellulosic particles by a thermoset through epoxide-hydroxyl reactions. As an example for lignocellulosic biomass, Eastern redcedar was employed. Using scanning fluorescence microscopy and vibrational spectroscopy, macroscopic to molecular scale interactions of the thermoset with the lignocellulose have been revealed. Impregnation of the polymer resin into the biomass cellular network by capillary action as well as applied pressure results in a self-organizing structure in the form of thermoset microrods in a matrix of lignocellulose. We also infer permeation of the thermoset into the cell walls from the reaction of epoxides with the hydroxyls of the lignin. Compression tests reveal, at 30% thermoset content, thermoset-cross-linked lignocellulose has superior mechanical properties over a commercial wood plastic composite while comparable stiffness and strength to bulk epoxy and wood, respectively. The failure mechanism is understood to be crack propagation along the particle-thermoset interface and/or interparticle thermoset network.

Stimuli responsive release of metalic nanoparticles on semiconductor substrates.

Optically active metal nanoparticles have been of recent and broad interest for applications to biomarker detection because of their ability to enable high sensitivity enhancements in various optical detection techniques. Here, we report stimuli responsive release of metallic nanoparticles on a semiconductor thin film array structure based on pH change. The metallic nanoparticles are obtained by a simple redox procedure on the semiconductor surface. This approach allows controlling nanoparticle surface coatings in situ for biomolecule conjugation, such as DNA probes on nanoparticles, and rapid stimuli responsive release of these nanoparticles upon pH change.

Charge-selective Raman scattering and fluorescence quenching by "nanometal on semiconductor" substrates.

Ag nanoparticles synthesized on n and p-type Si were shown to exhibit charge-selective surface-enhanced Raman scattering and fluorescence quenching. As revealed by electric force microscopy, the polarity and magnitude of the nanoparticle charge is controllable with the metal-semiconductor Fermi level difference and nanoparticle size. It is inferred that the Fermi level alignment is dominantly contributed by the charge-induced nanoparticle voltage. Nanoparticle charging also accounts for self-inhibition of coalescence during chemical reduction, allowing strong plasmon hybridization.

Surface-enhanced Raman scattering captures conformational changes of single photoactive yellow protein molecules under photoexcitation.

Distinct conformational changes of single photoactive yellow protein (PYP) molecules were captured under photoexcitation, using a SERS substrate approach. These steps conform to those in PYP's photocycle. At the single molecule level, SERS of PYP yields well-resolved peaks, some of which were not reported earlier. Further, exclusive peak pairs have been identified that can elucidate PYP's conformational steps and chemisorption configuration on Ag using the SERS selection rules. Despite the "weak chemisorption" of PYP on silver that only allows the single molecule signal to sustain for approximately 1 s, this duration may be long enough to resolve PYP's photocycle (approximately 0.3 s).

A "grow-in-place" architecture and methodology for electrochemical synthesis of conducting polymer nanoribbon device arrays.

Fully enclosed horizontal nanochannels, in a prearranged array on a substrate and with built-in electrical contacts and chemical access regions, were used as growth templates for electrochemical synthesis of conducting polymer nanoribbons. In this "grow-in-place" approach, the nanochannel templates are part of the final array structure and remain after fabrication of the nanoribbons. The built-in electrical contacts, which provide the electrical potential for electrochemical polymerization, also remain and become contacts/interconnects to the array components. The grow-in-place architecture and methodology remove the need for template dissolution, any post-synthesis nanoribbon "grow-and-then-place" manipulation, and any post-synthesis electrical contacting. The fact that the templates are fully enclosed prohibits dendrite formation during growth, ensures precise dimensionality, and gives the encapsulation needed in any real device application. In this report the grow-in-place approach to electrochemical polymerization is used to produce polyaniline nanoribbons. These were found to be fibrils and not tubes and to grow from the central region of the growth-template cross-section and not from the template walls. Two-point and four-point electrical characterization of these polyaniline nanoribbons, obtained using the built-in electrodes, was employed to yield the true polyaniline conductivity and to assess the ohmicity of the contacting approach. Conductivity studies, done as a function of nanoribbon width, show conductivity increases as the width decreases. We also show that our grow-in-place approach may be used for chemical polymerization. However, at least for polyaniline, electrochemical polymerization is superior since it does not suffer from diffusion-limited growth and allows precise placement of the nanoribbons in the growth channel.

Electroless synthesis of Ag nanoparticles on deposited nanostructured Si films.

Two and three-dimensional Ag nanoparticle ensembles were synthesized on deposited nanostructured column-void Si films simply by film immersion into pure Ag(2)SO(4) or AgNO(3) solutions. In addition to functioning as a reducer, this nanostructured material provides immobilization and monodispersion of the Ag nanoparticles due to its systematic nanoscale topography. This is accomplished without the requirement of a surfactant, capping agent, or linker. Kinetics, as monitored from plasmon optical extinction, and infrared spectroscopy suggest accompanying oxide growth limits and finally inhibits synthesis enabling nanoparticle size control. Kinetics is also limited by Ag+ transport through the voids unless the Si film is ultrathin. Our synthesis approach offers significant advantages for surface-enhanced molecular detection, including the absence of any agents on the nanoparticle surfaces and the ability to obtain nanoparticle ensembles on any substrate.