Karl S. Booksh

Omnidirectionally Stretchable High-Performance Supercapacitor Based on Isotropic Buckled Carbon Nanotube Films.

The emergence of stretchable electronic devices has attracted intensive attention. However, most of the existing stretchable electronic devices can generally be stretched only in one specific direction and show limited specific capacitance and energy density. Here, we report a stretchable isotropic buckled carbon nanotube (CNT) film, which is used as electrodes for supercapacitors with low sheet resistance, high omnidirectional stretchability, and electro-mechanical stability under repeated stretching. After acid treatment of the CNT film followed by electrochemical deposition of polyaniline (PANI), the resulting isotropic buckled acid treated CNT@PANI electrode exhibits high specific capacitance of 1147.12 mF cm(-2) at 10 mV s(-1). The supercapacitor possesses high energy density from 31.56 to 50.98 μWh cm(-2) and corresponding power density changing from 2.294 to 28.404 mW cm(-2) at the scan rate from 10 to 200 mV s(-1). Also, the supercapacitor can sustain an omnidirectional strain of 200%, which is twice the maximum strain of biaxially stretchable supercapacitors based on CNT assemblies reported in the literature. Moreover, the capacitive performance is even enhanced to 1160.43-1230.61 mF cm(-2) during uniaxial, biaxial, and omnidirectional elongations.

Discourse on the utilization of polyaniline coatings for surface plasmon resonance sensing of ammonia vapor.

Surface plasmon resonance spectroscopy is sensitive to near-surface (<300 nm) chemical and physical events that result in refractive index changes. The non-specific nature of the stimulus implies that chemical selectivity in SPR sensing configurations entirely relies upon the chemical recognition scheme employed. Biosensing applications commonly use surface layers composed of antibodies or enzymes for biomolecular recognition. Monitoring of volatile compounds with SPR spectroscopy, however, has not been widely discussed due to the difficulty in selectively responding to small molecules (<100 Da) in addition to the limited refractive index changes resulting from the interaction between the plasmon wave and volatile compounds. Different strategies explored thus far for sensing of small molecules have relied on optical and electrical changes of the recognition layer upon exposure to the analyte, yielding an indirect measurement. Examples of coatings used for gas-phase sensing with SPR include conducting metal oxides, polymers and organometallic dyes. Electrically conducting polymers, like polyaniline and polypyrrole, display dramatic conductivity changes in the presence of certain compounds. This property has resulted in their routine incorporation into different sensing schemes. However, application of electrically conducting polymers to SPR gas-phase sensing has been limited to a few examples, despite encouraging results. The emeraldine salt form of polyaniline (PAni) demonstrates a decreased electrical conductivity correlated to NH(3) concentration. In this contribution, PAni doped with camphorsulfonic acid (PAni-CSA) was applied to gas-phase sensing of NH(3) by way of SPR spectroscopy. Spectroscopic ellipsometry was used to determine the optical constants (n and k) for emeraldine salt and emeraldine base forms of PAni, confirming the wavelength-dependent response observed via SPR. The analytical performance of the coatings show that a limit of detection of 32 ppm NH(3) based on precision of the mass-flow controllers used and an estimated method limit of detection of ∼0.2 ppm based on three standard deviations of the blank. This is directly comparable to other, more established sensing architectures.

Fructose-water-dimethylsulfoxide interactions by vibrational spectroscopy and molecular dynamics simulations.

The solvation of fructose in dimethyl sulfoxide (DMSO) and DMSO-H(2)O (or DMSO-D(2)O) mixtures was investigated using vibrational spectroscopy (Raman, ATR/FTIR) and molecular dynamics (MD) simulations. The analysis of the fructose hydroxyl hydrogen-DMSO oxygen radial distribution function showed that the coordination number of DMSO around the furanose form of fructose is ~3.5. This number is smaller than the number of hydroxyl groups of fructose because one DMSO molecule is shared between two hydroxyl groups and because intramolecular hydrogen bonds are formed. In the case of fructose-DMSO mixtures, a red shift of the Raman S═O asymmetric stretch is observed, which indicates that fructose breaks the DMSO clusters through strong hydrogen bonding between the hydrogen atoms of its hydroxyl groups and the oxygen atom of DMSO. The Raman scattering cross sections of the DMSO S═O stretch when a DMSO molecule interacts with another DMSO molecule, a fructose molecule, or a water molecule were estimated from the spectra of the binary mixtures using the coordination numbers from MD simulations. It was also possible to use these values together with the MD-estimated coordination numbers to satisfactorily predict the effect of the water fraction on the Raman scattering intensity of the S═O stretching band in ternary mixtures. MD simulations also showed that, with increasing water content, the DMSO orientation around fructose changed, with the sulfur atom moving away from the carbohydrate. The deconvolution of the fructose IR OH stretching region revealed that the hydroxyls of fructose can be separated into two groups that participate in hydrogen bonds of different strengths. MD simulations showed that the three hydroxyls of the fructose ring form stronger hydrogen bonds with the solvent than the remaining hydroxyls, providing an explanation for the experimental observations. Finally, analysis of ATR/FTIR spectra revealed that, with increasing water content, the average hydrogen-bond enthalpy of the fructose hydroxyls decreases by ~2.5 kJ/mol.

Glucose detection with surface plasmon resonance spectroscopy and molecularly imprinted hydrogel coatings.

Molecularly imprinted hydrogel membranes were developed and evaluated for detection of small analytes via surface plasmon resonance spectroscopy. Imprinting of glucose phosphate barium salt into a poly(allylamine hydrochloride) network covalently bound to gold surfaces yielded a selective sensor for glucose. Optimization of relative amounts of chemicals used for preparation of the hydrogel was performed to obtain highest sensitivity. Addition of gold nanoparticles into the hydrogel matrix significantly amplified its response and sensitivity due to the impact of gold nanoparticles on the refractive index of the sensing layer. Evaluation of its selectivity showed that the sensor displayed preferential recognition to glucose compared to structurally related sugars in addition to being unaffected by phosphate as well as compounds containing amine groups, like creatinine. The detection limit of glucose in deionized water was calculated to be 0.02 mg/mL. The developed sensor was finally exposed to human urine spiked with glucose illustrating the coatings ability to re-bind the analyte in complex matrices. While the working concentration range in water was determined to be suitable for glucose monitoring in diabetic individuals at physiological levels, the detection in urine was determined to be 0.12 mg/mL. The decreased performance in urine provided an initial perspective on the difficulties associated with measurements in complex media.

Characterization of a Variable Angle Reflection Fourier Transform Infrared Accessory Modified for Surface Plasmon Resonance Spectroscopy

The Harrick AutoSeagull variable angle reflection accessory for Fourier transform infrared (FT-IR) spectrometers provides access to various spectroscopic techniques in a highly flexible platform. In particular, its ability to perform total internal reflection measurements is of interest because it also forms the basis for surface plasmon resonance (SPR) spectroscopy in prism-based configurations. The work presented here discusses the modification of the AutoSeagull to perform SPR spectroscopy, allowing for easy incorporation of the technique into most common FT-IR spectrometers. The wavelength dependency of the dielectric constant of the plasmon-supporting metal (in our case, gold) is largely responsible for the sensitivity attributed to changes in the samples refractive index (RI) monitored by SPR spectroscopy. Furthermore, the optical properties of gold are such that when near-infrared (NIR) and/or mid-infrared (mid-IR) wavelengths are used to excite surface plasmons, higher sensitivities to RI changes are experienced compared to surface plasmons excited with visible wavelengths. The result is that in addition to instrumental simplicity, SPR analysis on FT-IR spectrometers, as permitted by the modified AutoSeagull, also benefits from the wavelength ranges accessible. Adaptation of the AutoSeagull to SPR spectroscopy involved the incorporation of slit apertures to minimize the angular spread reaching the detector, resulting in sharper SPR “dips” but at the cost of noisier spectra. In addition, discussion of the systems analytical performance includes comparison of dip quality as a function of slit size, tailoring of the dip minima location with respect to incident angle, and sensitivity to bulk RI changes.

Characterization of electrografted 4-aminophenylalanine layers for low non-specific binding of proteins

Novel diazonium salts based on the 4-amino derivative of phenylalanine were electrografted onto gold surfaces with the ultimate goal of formation of surfaces resistant to nonspecific adsorption of proteins. A pulsed potential deposition profile was used instead of the more conventional approaches in order to circumvent mass-transport limitations. The influence of the deposition parameters, including pulse potentials, pulse width and number of pulses, with respect to electrode coverage was evaluated as a function of the blocking effect towards the diffusion of Fe(CN)64−/3− to electrode surfaces. By appropriately choosing the deposition parameters, peak potential differences (ΔEp) of ∼750 mV (for ν = 100 mV s−1), contrasting the ∼440 mV obtained for layers deposited via conventional electrochemical methods. FT-IR spectra confirm that the general structure of the electografted layers displays the same chemical functionality as the precursor molecule. Furthermore, the presence of the carboxylic acid group, characterized by the absorption feature at 1724 cm−1, indicates that the layers retain the ability to undergo post-deposition functionalization with bioreceptors. Ellipsometric analysis demonstrates the versatility of this method by depositing layers ranging from ∼1 to ∼24 nm thick. Finally, surface plasmon resonance spectroscopy was used to monitor the modified surfaces upon exposure to highly fouling media (76 mg mL−1 bovine serum albumin in phosphate buffered saline solution). A protein surface coverage equivalent to 62 ng cm−2 was measured, representing a significant improvement compared with more established antifouling layers based on polyethylene glycol (100 ng cm−2) and alkanethiol self-assembled monolayers (268 ng cm−2). The resistance towards nonspecific adsorption may be associated with the hydration layer tightly bound by the ionic charges present in the organic layer at physiological pH.

Shock-metamorphosed rutile grains containing the high-pressure polymorph TiO2-II in four Neoarchean spherule layers

At least 17 spherule layers are presently known within stratigraphic units depositednbetween ca. 3.47 and 2.49 Ga. The spherule layers contain varying amounts of formerlynmolten, millimeter-sized and smaller spherules. The aggregate thickness of spherules innthese layers commonly ranges from ∼1 cm to as much as a few decimeters. Several lines ofnevidence support the interpretation that the spherule layers represent distal impact ejectanlayers. Previously, only one shock-metamorphosed grain (quartz) had been documentednfrom the spherule layers. Therefore, a key diagnostic criterion for the impact origin of thesenlayers has remained elusive for 30 years. We report the discovery, using micro-Raman spectroscopy,nof shock-induced TiO 2 -II, a high-pressure polymorph of TiO 2 , in 34 grains fromnfour Neoarchean spherule layers deposited between ca. 2.65 and 2.54 Ga. As all the TiO 2 -II-bearing ngrains contain rutile, we interpret them as shock-metamorphosed rutile grains.nShock-metamorphosed rutile grains, which may be more abundant in the upper parts ofnthree of the layers, provide unambiguous physical evidence to further support an impactnorigin for these four layers. Our results demonstrate that TiO 2 -II can survive for >2.5 b.y. innsupracrustal successions that have undergone low-grade metamorphism. Because TiO 2 -IIntransforms to rutile at a temperature ≥440 °C, TiO 2 -II in impact ejecta layers is a potentialngeothermometer. To our knowledge, this is the first report of a shock-induced, high-pressurenpolymorph formed by an Archean impact.

Chemically responsive hydrogel with nanoparticle enhanced detection for small biomolecules

A surface plasmon resonance (SPR) sensor to quantify glucose using a molecularly imprinted polymer was developed. The polymer was prepared by crosslinking poly(allylamine) in the presence of glucose phosphate, monobarium salt (GPS-Ba) and attached to a thin film of gold (50 nm) which had been sputtered on top of a glass slide, via amide coupling. Upon removal of the template, this sensor was used to detect glucose in human urine in physiologically significant levels (1-20 mg/ml). Signal enhancement of the glucose sensor was made possible by incorporating gold nanoparticles in the polymer.

Raman Microspectroscopic Mapping with Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) Applied to the High-Pressure Polymorph of Titanium Dioxide, TiO2-II

The high-pressure, α-PbO2-structured polymorph of titanium dioxide (TiO2-II) was recently identified in micrometer-sized grains recovered from four Neoarchean spherule layers deposited between ∼2.65 and ∼2.54 billion years ago. Several lines of evidence support the interpretation that these layers represent distal impact ejecta layers. The presence of shock-induced TiO2-II provides physical evidence to further support an impact origin for these spherule layers. Detailed characterization of the distribution of TiO2-II in these grains may be useful for correlating the layers, estimating the paleodistances of the layers from their source craters, and providing insight into the formation of the TiO2-II. Here we report the investigation of TiO2-II-bearing grains from these four spherule layers using multivariate curve resolution–alternating least squares (MCR-ALS) applied to Raman microspectroscopic mapping. Raman spectra provide evidence of grains consisting primarily of rutile (TiO2) and TiO2-II, as shown by Raman bands at 174u2009cm–1 (TiO2-II), 426u2009cm–1 (TiO2-II), 443u2009cm–1 (rutile), and 610u2009cm–1 (rutile). Principal component analysis (PCA) yielded a predominantly three-phase system comprised of rutile, TiO2-II, and substrate-adhesive epoxy. Scanning electron microscopy (SEM) suggests heterogeneous grains containing polydispersed micrometer- and submicrometer-sized particles. Multivariate curve resolution–alternating least squares applied to the Raman microspectroscopic mapping yielded up to five distinct chemical components: three phases of TiO2 (rutile, TiO2-II, and anatase), quartz (SiO2), and substrate-adhesive epoxy. Spectral profiles and spatially resolved chemical maps of the pure chemical components were generated using MCR-ALS applied to the Raman microspectroscopic maps. The spatial resolution of the Raman microspectroscopic maps was enhanced in comparable, cost-effective analysis times by limiting spectral resolution and optimizing spectral acquisition parameters. Using the resolved spectra of TiO2-II generated from MCR-ALS analysis, a Raman spectrum for pure TiO2-II was estimated to further facilitate its identification.

Coaxial fiber-optic chemical-sensing excitation–emission matrix fluorometer

Great reductions in the overall size and complexity of high throughput multichannel UV-visible fluorometers were achieved by coupling a compact optical fiber array to compact dispersive transmission optics. The coaxial configuration centers on the insertion of a silica/silica optical fiber into the hollow region of a UV-fused silica capillary waveguide. The outer core delivers the maximum power of the narrow wavelength region of the excitation spectrum created by coupling a xenon arc discharge lamp to a compact spectrometer. The molecular fluorescence resulting from the interaction of light emitted at the distal end of the hollow waveguide and the sample matrix is received and transmitted to a CCD via a compact dispersive grating-prism (grism) optical assembly. A linear array of the coaxial optical fibers permits a full excitation-emission matrix spectrum of the analyte matrix to be projected onto the face of the CCD. The in situ identification and monitoring of polycyclic aromatic hydrocarbons was carried out for the initial application testing for this prototype.