Automatic baseline correction of vibrational circular dichroism spectra.

A three-phase, computational method for the baseline correction of vibrational circular dichroism (VCD) spectra has been proposed. In the first phase the raw spectrum is subdivided into m segments (or regions) resulting in p rough estimates of the baseline. A second phase uses gradient characteristics to discriminate between baseline and band response for each baseline, in turn. In the final phase all baselines are interrogated simultaneously by assigning the median estimate of each differential response's distribution to the true baseline. Using VCD spectra of (R)-camphor as test cases, this work demonstrated that the accurate removal of baseline components is readily achievable with minimal user intervention. Baseline correction also demonstrated flexibility in that prior information, such as the symmetry of a baselinefree VCD spectrum, is readily used during the correction protocol. Although three adjustable parameters are present in the base algorithm, optimal performance and full automation were attainable following the use of analysis of variance (ANOVA) to analyze simulated bipolar spectra. These ANOVAs suggested that band point discrimination could be discarded and the remaining two default parameters adopted.

Comparison of electromagnetic shielding with polyaniline nanopowders produced in solvent-limited conditions.

Nanoparticle synthesis (~10-50 nm) of HCl-doped polyaniline elucidates the impact of limiting solvent (water) and oxidizing agent (ammonium peroxydisulfate) on morphology (XRD and TEM), chemical structure (FTIR), conductivity (two-point DC) and electromagnetic shielding effectiveness (SE) in microwave frequencies (i.e., X-band S-parameter measurements). Detailed comparison of these properties with respect to three distinct polymerization environments indicate that a solvent-free or limited solvent polymerization accomplished through a wet grinding solid-phase reaction produces superior conductivity (27 S/cm) with intermediate crystallinity (66%) for the highest EM shielding-an order of magnitude improvement over conventional polymerization with respect to EM power transmission reduction for all loadings per shielding area (0.04 to 0.17 g/cm(2)). By contrast, the classic oxidation of aniline in a well-dispersed aqueous reaction phase with an abundance of available oxidant in free solution yielded low conductivity (3.3 S/cm), crystallinity (54%), and SE, whereas similar solvent-rich reactions with limiting oxidizer produced similar conductivity (2.9 S/cm) and significantly lower SE with the highest crystallinity (72%). This work is the first to demonstrate that limiting solvent and oxidizer enhances electromagnetic interactions for shielding microwaves in polyaniline nanopowders. This appears connected to having the highest overall extent of oxidation achieved in the wet solid-phase reaction.

Detection of receptor-induced glycoprotein conformational changes on enveloped virions by using confocal micro-Raman spectroscopy.

Conformational changes in the glycoproteins of enveloped viruses are critical for membrane fusion, which enables viral entry into cells and the pathological cell-cell fusion (syncytia) associated with some viral infections. However, technological capabilities for identifying viral glycoproteins and their conformational changes on actual enveloped virus surfaces are generally scarce, challenging, and time-consuming. Our model, Nipah virus (NiV), is a syncytium-forming biosafety level 4 pathogen with a high mortality rate (40 to 75%) in humans. Once the NiV attachment glycoprotein (G) (NiV-G) binds the cell receptor ephrinB2 or -B3, G triggers conformational changes in the fusion glycoprotein (F) that result in membrane fusion and viral entry. We demonstrate that confocal micro-Raman spectroscopy can, within minutes, simultaneously identify specific G and F glycoprotein signals and receptor-induced conformational changes in NiV-F on NiV virus-like particles (VLPs). First, we identified reproducible G- and F-specific Raman spectral features on NiV VLPs containing M (assembly matrix protein), G, and/or F or on NiV/vesicular stomatitis virus (VSV) pseudotyped virions via second-derivative transformations and principal component analysis (PCA). Statistical analyses validated our PCA models. Dynamic temperature-induced conformational changes in F and G or receptor-induced target membrane-dependent conformational changes in F were monitored in NiV pseudovirions in situ in real time by confocal micro-Raman spectroscopy. Advantageously, Raman spectroscopy can identify specific protein signals in relatively impure samples. Thus, this proof-of-principle technological development has implications for the rapid identification and biostability characterization of viruses in medical, veterinary, and food samples and for the analysis of virion glycoprotein conformational changes in situ during viral entry.

Multivariate analysis of micro-Raman spectra of thermoplastic polyurethane blends using principal component analysis and principal component regression.

Probing the specific hydrogen-bonding behavior of thermoplastic polyurethane (TPU) blends using vibrational spectroscopies remains the sin qua non for understanding the link between hydrogen-bonding and phase-segregation behavior. However, current literature holds to more traditional univariate approaches when studying the morphologically interesting normal molecular vibrations of TPUs. In the present study, multivariate analysis, including principal component analysis (PCA) and principal component regression (PCR), is used to scrutinize the relevant Raman bands acquired from a binary mixture of analogous TPU copolymer blends. Considering the near identical behavior of selected spectral regions, PCA was capable of isolating linear and nonlinear composition-dependent trends on PC-scores plots. From here, the PC scores, extracted from wavelengths comprising the carbonyl stretching region (1681-1764 cm(-1)), CH(2) deformations (1380-1500 cm(-1)), aromatic stretch from the hard segment (1617 cm(-1)), and amide II mixed band (1540 cm(-1)), were used to explicitly predict the mole fraction of hard segment present in each blend using PCR. Spectral preprocessing, wavelength selection, and variable scaling were major factors in PCR accurately predicting the weight fraction of each copolymer in spite of the clearly evident, blend-specific spectroscopic behavior.

Comprehensive detection and discrimination of Campylobacter species by use of confocal micro-Raman spectroscopy and multilocus sequence typing.

A novel strategy for the rapid detection and identification of traditional and emerging Campylobacter strains based upon Raman spectroscopy (532 nm) is presented here. A total of 200 reference strains and clinical isolates of 11 different Campylobacter species recovered from infected animals and humans from China and North America were used to establish a global Raman spectroscopy-based dendrogram model for Campylobacter identification to the species level and cross validated for its feasibility to predict Campylobacter-associated food-borne outbreaks. Bayesian probability coupled with Monte Carlo estimation was employed to validate the established Raman classification model on the basis of the selected principal components, mainly protein secondary structures, on the Campylobacter cell membrane. This Raman spectroscopy-based typing technique correlates well with multilocus sequence typing and has an average recognition rate of 97.21%. Discriminatory power for the Raman classification model had a Simpson index of diversity of 0.968. Intra- and interlaboratory reproducibility with different instrumentation yielded differentiation index values of 4.79 to 6.03 for wave numbers between 1,800 and 650 cm(-1) and demonstrated the feasibility of using this spectroscopic method at different laboratories. Our Raman spectroscopy-based partial least-squares regression model could precisely discriminate and quantify the actual concentration of a specific Campylobacter strain in a bacterial mixture (regression coefficient, >0.98; residual prediction deviation, >7.88). A standard protocol for sample preparation, spectral collection, model validation, and data analyses was established for the Raman spectroscopic technique. Raman spectroscopy may have advantages over traditional genotyping methods for bacterial epidemiology, such as detection speed and accuracy of identification to the species level.

DNA detection on lateral flow test strips: enhanced signal sensitivity using LNA-conjugated gold nanoparticles.

A lateral flow test strip assay, enabling sensitive detection of DNA specific to the foodborne pathogen E. coli O157:H7, is described. The use of LNA-conjugated gold nanoparticle probes, along with signal amplification protocols, results in minimum detectable concentrations of ~0.4 nM.

Automatic baseline subtraction of vibrational spectra using minima identification and discrimination via adaptive, least-squares thresholding.

A method of automated baseline correction has been developed and applied to Raman spectra with a low signal-to-noise ratio and surface-enhanced infrared absorption (SEIRA) spectra with bipolar bands. Baseline correction is initiated by dividing the raw spectrum into equally spaced segments in which regional minima are located. Following identification, the minima are used to generate an intermediate second-derivative spectrum where points are assigned as baseline if they reside within a locally defined threshold region. The threshold region is similar to a confidence interval encountered in statistics. To restrain baseline and band point discrimination to the local level, the calculation of the confidence region employs only a predefined number of already-accepted baseline minima as part of the sample set. Statistically based threshold criteria allow the procedure to make an unbiased assessment of baseline points regardless of the behavior of vibrational bands. Furthermore, the threshold region is adaptive in that it is further modified to consider abrupt changes in baseline. The present procedure is model-free insofar as it makes no assumption about the precise nature of the perturbing baseline nor requires treatment of spectra prior to execution.

Rheological and micro-Raman time-series characterization of enzyme sol-gel solution toward morphological control of electrospun fibers.

Rheological and micro-Raman time-series characterizations were used to investigate the chemical evolutionary changes of silica sol-gel mixtures for electrospinning fibers to immobilize an enzyme (tyrosinase). Results of dynamic rheological measurements agreed with the expected structural transitions associated with reacting sol-gel systems. The electrospinning sols exhibited shear-thinning behavior typical of a power law model. Ultrafine (200-300 nm diameter) fibers were produced at early and late times within the reaction window of approximately one hour from initial mixing of sol solutions with and without enzyme; diameter distributions of these fibers showed much smaller deviations than expected. The enzyme markedly increased magnitudes of both elastic and viscous moduli but had no significant impact on final fiber diameters, suggesting that the shear-thinning behavior of both sol-gel mixtures is dominant in the fiber elongation process. The time course and scale for the electrospinning batch fabrication show strong correlations between the magnitudes in rheological property changes over time and the chemical functional group evolution obtained from micro-Raman time-series analysis of the reacting sol-gel systems.

Investigating antibacterial effects of garlic (Allium sativum) concentrate and garlic-derived organosulfur compounds on Campylobacter jejuni by using Fourier transform infrared spectroscopy, Raman spectroscopy, and electron microscopy.

Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy were used to study the cell injury and inactivation of Campylobacter jejuni from exposure to antioxidants from garlic. C. jejuni was treated with various concentrations of garlic concentrate and garlic-derived organosulfur compounds in growth media and saline at 4, 22, and 35°C. The antimicrobial activities of the diallyl sulfides increased with the number of sulfur atoms (diallyl sulfide < diallyl disulfide < diallyl trisulfide). FT-IR spectroscopy confirmed that organosulfur compounds are responsible for the substantial antimicrobial activity of garlic, much greater than those of garlic phenolic compounds, as indicated by changes in the spectral features of proteins, lipids, and polysaccharides in the bacterial cell membranes. Confocal Raman microscopy (532-nm-gold-particle substrate) and Raman mapping of a single bacterium confirmed the intracellular uptake of sulfur and phenolic components. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to verify cell damage. Principal-component analysis (PCA), discriminant function analysis (DFA), and soft independent modeling of class analogs (SIMCA) were performed, and results were cross validated to differentiate bacteria based upon the degree of cell injury. Partial least-squares regression (PLSR) was employed to quantify and predict actual numbers of healthy and injured bacterial cells remaining following treatment. PLSR-based loading plots were investigated to further verify the changes in the cell membrane of C. jejuni treated with organosulfur compounds. We demonstrated that bacterial injury and inactivation could be accurately investigated by complementary infrared and Raman spectroscopies using a chemical-based, "whole-organism fingerprint" with the aid of chemometrics and electron microscopy.

Infrared and Raman spectroscopic studies of the antimicrobial effects of garlic concentrates and diallyl constituents on foodborne pathogens.

The antimicrobial effects of garlic (Allium sativum) extract (25, 50, 75, 100, and 200 µL/ml) and diallyl sulfide (5, 10, and 20 µM) on Listeria monocytogenes and Escherichia coli O157:H7 cultivated in tryptic soy broth at 4, 22, and 35 °C for up to 7 days were investigated. L. monocytogenes was more resistant to garlic extract and diallyl compounds treatment than E. coli O157:H7. Fourier transform infrared (FT-IR) spectroscopy indicated that diallyl constituents contributed more to the antimicrobial effect than phenolic compounds. This effect was verified by Raman spectroscopy and Raman mapping on single bacteria. Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed cell membrane damage consistent with spectroscopic observation. The degree of bacterial cell injury could be quantified using chemometric methods.

8-aminoquinoline functionalized silica nanoparticles: a fluorescent nanosensor for detection of divalent zinc in aqueous and in yeast cell suspension.

Zinc is one of the most important transition metal of physiological importance, existing primarily as a divalent cation. A number of sensors have been developed for Zn(II) detection. Here, we present a novel fluorescent nanosensor for Zn(II) detection using a derivative of 8-aminoquinoline (N-(quinolin-8-yl)-2-(3 (triethoxysilyl)propylamino)acetamide (QTEPA) grafted on silica nanoparticles (SiNPs). These functionalized SiNPs were used to demonstrate specific detection of Zn(II) in tris-HCl buffer (pH 7.22), in yeast cell (Saccharomyces cerevisiae) suspension, and in tap water. The silane QTEPA, SiNPs and final product were characterized using solution and solid state nuclear magnetic resonance, Fourier transform infrared, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, elemental analysis, thermogravimetric techniques, and fluorescence spectroscopy. The nanosensor shows almost 2.8-fold fluorescence emission enhancement and about 55 nm red-shift upon excitation with 330 ± 5 nm wavelength in presence of 1 µM Zn(II) ions in tris-HCl (pH 7.22). The presence of other metal ions has no observable effect on the sensitivity and selectivity of nanosensor. This sensor selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 µM. The sensor shows good applicability in the determination of Zn(II) in tris-HCl buffer and yeast cell environment. Further, it shows enhancement in fluorescence intensity in tap water samples.

Determination of total phenolic content and antioxidant activity of garlic (Allium sativum) and elephant garlic (Allium ampeloprasum) by attenuated total reflectance-Fourier transformed infrared spectroscopy.

The total phenolic contents and antioxidant activities of garlics from California, Oregon, Washington, and New York were determined by Fourier transform infrared (FT-IR) spectroscopy (400-4000 cm(-1)). The total phenolic content was quantified [Folin-Ciocalteu assay (FC)] and three antioxidant activity assays, 2,2-diphenyl-picrylhydrazyl (DPPH) assay, Trolox equivalent antioxidant capacity (TEAC) assay, and ferric reducing antioxidant power (FRAP), were employed for reference measurements. Four independent partial least-squares regression (PLSR) models were constructed with spectra from 25 extracts and their corresponding FC, DPPH, TEAC, and FRAP with values for 20 additional extracts predicted (R > 0.95). The standard errors of calibration and standard error of cross-validation were <1.45 (TEAC), 0.36 (FRAP), and 0.33 µmol Trolox/g FW (DPPH) and 0.55 mg gallic acid/g FW (FC). Cluster and dendrogram analyses could segregate garlic grown at different locations. Hydroxyl and phenolic functional groups most closely correlated with garlic antioxidant activity.

Fluorescence sensing of zinc(II) using ordered mesoporous silica material (MCM-41) functionalized with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide.

A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission electron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA-modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 µM Zn(II) ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ± 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 µM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation.

Substrate effects on the wettability of electrospun titania-poly(vinylpyrrolidone) fiber mats.

Titania-poly(vinylpyrrolidone) (PVP) core-shell nano/microfibers are electrospun on substrates of differing hydrophilicity and conductivity in order to investigate the connection between these substrate properties and the apparent water contact angles against the fiber mats. The focus of this study compares current data from silicon- and aluminum foil-supported mats to extant data from ITO and glass-supported fibers to detail the complexities of apparent contact angle dependence on mat structure related to substrate properties. Electrospinning time and collection distance were controlled parameters for producing thicker and denser mats. In all cases, contact angles increased with collection time for a given substrate series. A morphological wettability study of the fiber mat surface was conducted by applying Rhodamine B dye solution droplets. Using fluorescence microscopy, the stained fibers indicate the extent of true wetting contact and the lack of penetration into the fiber layers. Image comparisons with bright-field illumination confirms that even some fibers of the top layers are not wetted.

Winkler boundary conditions for three-point bending tests on 1D nanomaterials.

Bending tests with atomic force microscopes (AFM) is a common method for elasticity measurements on 1D nanomaterials. Interpretation of the force and deflection data is necessary to determine the Young's modulus of the tested material and has been done assuming either of two classic boundary conditions that represent two extreme possibilities for the rigidity of the sample-anchor interface. The elasticity results from the two boundary conditions differ by a factor of four. Furthermore, both boundary conditions ignore the effects of deflections in the anchors themselves. The Winkler model for beams on elastic foundations is developed here for three-point bending tests to provide a more realistic representation. Equations for computing sample elasticity are derived from two sets of boundary conditions for the Winkler model. Application of this model to interpret the measurement of mechanical stiffness of a silica nanowire at multiple points in a three-point bending is discussed. With the correct choice of boundary conditions, the Winkler model gives a better fit for the observed stiffness profile than the classical beam models while providing a result that differs from both by a factor of two and is comparable to the bulk elasticity.

Wettability of electrospun poly(vinylpyrrolidone)-titania fiber mats on glass and ITO substrates in aqueous media.

Networks of nano/microfibers (fiber mats) have been electrospun from solutions of dispersed poly(vinylpyrrolidone) (PVP) and a titania precursor onto glass and indium-tin oxide (ITO) plates to study their wettability. Collection time and electrode separation are the two key fabrication parameters investigated, along with the flow rate, polymer molecular weight, and drying conditions, to determine the effects on network morphology and the relationship to contact angles. Measurements indicate that the fiber mats on both glass and ITO increase in thickness and contact angle for longer spinning time and shorter distance, resulting in an extreme case of apparent ultrahydrophobicity on ITO of up to 169.9 degrees with water. The fiber mats are shown by optical microscopy to exhibit differences in morphology for insulating glass (straight) and conductive ITO (loopy) substrates responsible for the wide-ranging and well-controlled wettability to within 1-2 degrees. Fiber mats baked at 200 degrees C for 24 h show excellent mechanical stability with wetting even against frequent heavy rinsing, conducive for reusable aqueous applications such as biosensors or cellular scaffolding.

Nanomechanical measurements with AFM in the elastic limit.

With increasing interest in nanoscience and nanotechnology, the fundamental underpinnings of what makes materials strong and durable are under critical investigation. Recent findings suggest that when materials are reduced in extent to nanoscopic proportions, they exhibit enhanced strength, specifically in the form of higher moduli than are measured on macroscopic objects of the same composition. Force-deformation behavior of nanostructures subjected to concentrated loads, such as with atomic force microscopy (AFM), can yield detailed information and insight about their local mechanical properties. We review and evaluate the effectiveness of deformation and indentation tests used in determining the elastic modulus of nanobeams, nanosprings, thin films, biological samples, dendrimers, and fluid droplets. Obstacles yet remain in the determination of absolute, quantitative modulus data at the nanoscale. In spite of basic limitations, recent developments in advanced nanomechanical techniques will facilitate improvement in our understanding of material strength and aging from molecules and colloids to the macroscale.

Polymer nanowire elastic moduli measured with digital pulsed force mode AFM.

The mechanical bending behavior of polymer nanowires-polypyrrole and poly(3,4-ethylene dioxythiophene-co-styrene sulfonate)-produced by template molding were measured using a new innovation in atomic force microscopy (AFM). Digital pulsed force mode (DPFM) was used to image and simultaneously perform three-point bend tests along nanowires spanning microchannels in silicon. The bending profiles were analyzed for apparent elastic moduli variations along the suspended length of individually isolated nanowires and compared to classic beam deflection models for various geometric and boundary conditions. The elastic moduli calculated from these AFM data are 2-7 times that expected for bulk polymer values (approximately 1-3 GPa), demonstrating an apparent strengthening of nanostructured polymer even for diameters greater than 100 nm--the accepted boundary for nanoscience. Furthermore, detailed analysis of deflection data versus loading location demonstrates the experimental dependence on test geometry and inherent errors in relying solely on midpoint bending measurements or any single loading configuration for nanomechanical testing as well as the significant contribution of nanoindentation effects.

Counterion dependent dye aggregates: nanorods and nanorings of tetra(p-carboxyphenyl)porphyrin.

Atomic force microscopy (AFM) of porphyrin aggregates formed on silica from acidic aqueous solution is used to investigate the basis for the previously reported counterion dependence of the optical spectra of aggregates of H(2)TCPP(2+), the diacid form of tetra(p-carboxyphenyl)porphyrin (TCPP). Resonance light scattering confirms the presence of excitonically coupled porphyrin aggregates in solutions of H(2)TCPP(2+) in both aqueous HCl and HNO(3). Aggregates formed in aqueous HNO(3) solutions show resonance light scattering (RLS) at wavelengths within both the H and J aggregate absorption bands and are imaged on the surface of silica as nanorods about 3 to 4 nm in height. H(2)TCPP(2+) aggregates in aqueous HCl solution exhibit RLS when excited within the blue-shifted Soret band (H band) and produce AFM images on silica of ring-shaped structures ranging from about 200 to 2000 nm in diameter. Fluorescence excitation and emission spectra reveal quenching of the Q-band emission in the aggregates at a pH less than 1 and confirm the existence of a single species, assigned to a dimer, at a pH just above 1. The morphology of the nanostructures as revealed by AFM provides insight into the structural basis for the counterion-dependent optical properties of H(2)TCPP(2+) aggregates.

Structural evolution of octyltriethoxysilane films on glass surfaces during annealing at elevated temperature.

Glass samples treated by octyltriethoxysilane were annealed for times ranging from 0 to 16 h, and their topography, adhesion, and stiffness properties were examined using pulsed-force mode (PFM) atomic force microscopy. While the surfaces of samples dried at room temperature were structurally featureless, those annealed at 145 degrees C showed formation of islands, increasing in size and number with heating time. PFM adhesion and stiffness maps suggested that the glass substrate remained at least partially covered by silanes even after island formation.