Germanium Internal Reflection Element Research Articles

On the Widths of Bands in the Infrared Spectra of Oxyanions.

It is well known that the antisymmetric stretching (ν3) band in the mid-infrared spectra of oxyanion salts is usually very broad, whereas all the other fundamental bands are narrow. In this paper, we propose that the underlying cause of the increased width is the effect of the very high absorption index of this band for samples prepared with a range of particle sizes. When oxyanion salts are ground, the diameter of the resulting particles usually varies from less than 100 nm to about 2 µm. While the peak absorbance of the ν3 band of the smaller particles (diameter < 200 nm) is less than 1, that of the larger particles can be as high as 6. We show that the average transmittance of these particles leads to a significant band broadening, especially when there are small voids in the resulting sample. Although the effect is always seen in the spectra of alkali halide disks and mineral oil mulls, it is also seen in diffuse reflection and attenuated total reflection (ATR) spectra. Because the depth of penetration of infrared radiation below 1500 cm-1 is less than 1 µm for ATR spectra measured with a germanium internal reflection element (IRE), the width of the ν3 band is lower than that of ATR spectra measured with an IRE of lower refractive index such as diamond on zinc selenide.

Attenuated Total Reflection Surface-Enhanced Infrared Absorption (ATR SEIRA) Spectroscopy for the Analysis of Fatty Acids on Silver Nanoparticles.

The application of attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR SEIRA) to the analysis of fatty acids on silver nanoparticles was investigated. Attenuated total reflection measurements using four types of internal reflection elements (IREs)-zinc selenide, diamond, silicon, and germanium-were performed for silver nanoparticles modified with fatty acids, and germanium IRE was shown to be suitable for the analysis of silver nanoparticles, even when the sample had a high refractive index. Fatty acids coating the silver nanoparticles could be directly identified by SEIRA enhancement, because both symmetric carboxylate stretching vibration and methylene wagging vibration were strongly detected. Furthermore, the peak positions for methylene wagging vibration differed depending on the carbon number of the fatty acid, so that information from the ATR SEIRA spectra makes it possible to identify substances coating silver nanoparticles. Therefore, ATR SEIRA would appear to have significant potential as a technique for the identification of substances coated on metal nanoparticle surfaces.

Mapping Infrared Enhancement around Gold Nanoparticles Using Polyelectrolytes

Enhancement of infrared signals from polyelectrolyte adsorbed on gold nanoparticles (GNPs) was studied in situ by attenuated total reflection infrared spectroscopy. Nanoparticles and polyelectrolytes were deposited using layer-by-layer techniques, and the infrared signal was studied as a function of particle size, particle density, and distance from particle surface. It was observed that enhancement is more pronounced for larger nanoparticles and it decreases with increasing distance from the particle surface. Furthermore, at high GNP coverage, the signal from the first polyelectrolyte layer is particularly enhanced, and the signal increases slowly with time, in contrast to subsequent layers. We assign this to polyelectrolyte adsorption within narrow gaps between nanoparticles, where the electric field is enhanced. Furthermore, enhanced absorption was observed in the gap between the GNPs and the germanium internal reflection element, which was confirmed by polarized measurements. This enhancement is more ...

10 nm deep, sub-nanoliter fluidic nanochannels on germanium for attenuated total reflection infrared (ATR-IR) spectroscopy.

The fabrication of sub-nanoliter fluidic channels is demonstrated, with merely 10 nm depth on germanium, using conventional semiconductor device fabrication methods and a polymer assisted room-temperature sealing method. As a first application, an ultralow volume (650 pL) was studied by ATR-IR spectroscopy. A detection limit of ∼7.9 × 1010 molecules of human serum albumin (HSA) (∼0.2 mM) in D2O was achieved with highly specific ATR-IR spectroscopy.

Infrared Spectra Alteration in Water Proximate to the Palms of Therapeutic Practitioners

Through standard techniques of infrared (IR) spectrophotometry, sterile water samples in randomly selected sealed vials evidence alteration of infrared (IR) spectra after being proximate to the palms of the hands of both Practicing and Non-practicing Therapy Practitioners, each of whom employed a personal variation of the Laying-on-of-Hands/Therapeutic Touch processes. This pilot study presents 14 cases, involving 14 Practitioners and 14 Recipients. The first hypothesis, that a variation in the spectra of all (84) Treated spectra compared with all (57) Control spectra would be observed in the 2.5-3.0µm range, was confirmed (P = .02). Overall, 10% (15) of the spectra were done using a germanium internal reflection element (IRE), and 90% of the spectra (126) were done with a zinc selenide IRE. The difference in refractive index between the two IREs skews the data. The zinc selenide IRE spectra alone yield P = .005. The authors believe the most representative evidence for the effect appeared in the sample group of Treated vs Calibration Controls using the zinc selenide IRE (P = .0004). The second hypothesis, that there existed a direct relationship between intensity of effect and time of exposure, was not confirmed. This study replicates earlier findings under conditions of blindness, randomicity, and several levels of controls. Environmental factors are considered as explanations for the observed IR spectrum alteration, including temperature, barometric pressure, and variations dependent on sampling order. They do not appear to explain the effect.

Determination of the Adsorption of Xanthate on Mesoporous CuAl&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Using a Continuous Online &lt;em&gt;In situ&lt;/em&gt; ATR-FTIR Technology

In this study, mesoporous nano CuAl2O4 was synthesized through a coprecipitation method using simple mixed templates consisting of butylamine and dodecanol. The sample was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption-desorption techniques. The absorption of butyl and octyl xanthate from aqueous solution onto the synthesized mesoporous CuAl2O4 solid surfaces was studied by a continuous, online, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) technique. The CuAl2O4 membrane used in the adsorption experiments was prepared on a germanium internal reflection element using the chemical bath deposition method. During the adsorption process, the characteristic peak height of xanthate at 1200 and 1040 cm(-1) emerged and gradually increased. By monitoring changes in the peak height at 1200 cm(-1), which was assigned to the stretching vibration caused by C-O-C of the adsorbed xanthate molecules, the adsorption kinetics were studied. The adsorption results show that mesoporous CuAl2O4 has a high chemisorption capacity for xanthate, which reaches 236 and 300 mg.g(-1) for butyl and octyl xanthate, respectively, within 100 min. The adsorption kinetics can be described by a pseudo-second-order reaction model.

Quantitative Determination of Band Distortions in Diamond Attenuated Total Reflectance Infrared Spectra

Due to its unmatched hardness and chemical inertia, diamond offers many advantages over other materials for extreme conditions and routine analysis by attenuated total reflection (ATR) infrared spectroscopy. Its low refractive index can offer up to a 6-fold absorbance increase compared to germanium. Unfortunately, it also results for strong bands in spectral distortions compared to transmission experiments. The aim of this paper is to present a methodological approach to determine quantitatively the degree of the spectral distortions in ATR spectra. This approach requires the determination of the optical constants (refractive index and extinction coefficient) of the investigated sample. As a typical example, the optical constants of the fibroin protein of the silk worm Bombyx mori have been determined from the polarized ATR spectra obtained using both diamond and germanium internal reflection elements. The positions found for the amide I band by germanium and diamond ATR are respectively 6 and 17 cm(-1) lower than the true value dtermined from the k(nu) spectrum, which is calculated to be 1659 cm(-1). To determine quantitatively the effect of relevant parameters such as the film thickness and the protein concentration, various spectral simulations have also been performed. The use of a thinner film probed by light polarized in the plane of incidence and diluting the protein sample can help in obtaining ATR spectra that are closer to their transmittance counterparts. To extend this study to any system, the ATR distortion amplitude has been evaluated using spectral simulations performed for bands of various intensities and widths. From these simulations, a simple empirical relationship has been found to estimate the band shift from the experimental band height and width that could be of practical use for ATR users. This paper shows that the determination of optical constants provides an efficient way to recover the true spectrum shape and band frequencies of distorted ATR spectra.

The Advantages of an Attenuated Total Internal Reflection Infrared Microspectroscopic Imaging Approach for Kidney Biopsy Analysis

The benefits of an attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging approach for kidney biopsy analysis are described. Biopsy sections collected from kidney-stone formers are analyzed at the initial stages of stone development to provide insights into stone growth and formation. The majority of tissue analysis currently conducted with IR microspectroscopy is performed with a transflection method. The research presented in this manuscript demonstrates that ATR overcomes many of the disadvantages of transflection or transmission measurements for tissue analysis including an elimination of spectral artifacts. When kidney biopsies with small mineral inclusions are analyzed with a transflection approach, specular reflection and the Christiansen effect (anomalous dispersion) can occur, leading to spectral artifacts. Another effect specific to the analysis of mineral inclusions present in kidney biopsies is known as the reststrahlen effect whereby the inclusions become strong reflectors near an absorption band. ATR eliminates these effects by immersing the sample in a high index medium. Additionally, the focused beam size for ATR is decreased by a factor of four when a germanium internal reflection element is used, allowing the acquisition of spectra from small mineral inclusions several micrometers in diameter. If quantitative analysis of small mineral inclusions is ultimately desired, ATR provides the photometrically accurate spectra necessary for quantification.

Comparison between in situ Total Internal Reflection Vibrational Spectroscopy of an Adsorbed Collector and Spectra Calculated by Ab Initio Density Functional Theory Methods

In this investigation, adsorbed heptyl xanthate on a Ge(111) surface was studied, as well as the free heptyl xanthate molecule, by means of first-principle density functional theory calculations. The modeled results were compared with the in situ total internal reflection vibrational spectroscopy spectra of heptyl xanthate adsorbed on a germanium internal reflection element and the transmission infrared spectrum of a heptyl xanthate ion in aqueous solution. The assignments of the vibrational frequencies were done for the adsorbed xanthate. The region between 1150 and 1000 cm-1 seems suitable for discussing differences between an adsorbed xanthate and its corresponding ion. The modeled spectra for both the adsorbed xanthate and the xanthate ion are in good agreement with the experimentally retrieved spectra. This investigation shows the strength of using DFT calculations in the interpretation of absorption bands from molecules adsorbed at surfaces in situ.

Cure behavior of DGEBA vinyl ester–styrene resins near silane‐treated interfaces

AbstractAn experimental technique using FTIR‐ATR was developed for monitoring the copolymerization behavior of a DGEBA‐based vinyl ester (VE) and styrene (ST) near the surface of a germanium internal reflection element. The data were compared to previously obtained bulk measurements of the cure behavior. It was found that the extent of conversion may be slightly greater for ST and slightly lower for VE near an untreated interface compared to the bulk. The cure behavior of VE–ST in the vicinity of a germanium IRE surface treated with a styryl amine silane (Dow Corning Z‐6032) was also investigated. In this case the effect on the cure was more dramatic, as exhibited by a more rapid consumption of ST compared to VE, thus resulting in a greatly reduced final conversion of VE double bonds compared to the bulk. These results suggest that, in glass fiber–reinforced composites, such sizings could significantly alter the composition of the crosslinked network in the vicinity of a fiber surface with the potential for a lower Tg interphase being formed that is rich in homopolymerized styrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2784–2792, 2006

N-Heptyl xanthate adsorption on a ZnS layer synthesized on germanium: An in situ attenuated total reflection IR study

Adsorption of n-heptyl xanthate on synthesized zinc sulfide was followed in situ by monitoring the methylene absorption band at 2925 cm −1. The zinc sulfide surface used in the adsorption experiments was synthesized on a germanium internal reflection element using the chemical bath deposition method. Characterization of the adsorbent surface was performed by X-ray photoelectron spectroscopy. The time needed to reach adsorption equilibrium varied with the initial concentration of the aqueous potassium heptyl xanthate solution. The amount of adsorbed xanthate ions increased with the concentration of the solution within the range studied (10 μM–50 mM). The experimental data are reasonably well described by the Langmuir adsorption isotherm. Polarized infrared attenuated total reflection (ATR) was used to determine the average orientation of the heptyl chains by measuring the absorbance of the infrared beam polarized perpendicularly and parallely to the plane of incidence. Measured absorbances were corrected for contribution from heptyl xanthate in bulk solution.

Reversible immobilization of peptides: surface modification and in situ detection by attenuated total reflection FTIR spectroscopy.

A generic method is described for the reversible immobilization of polyhistidine-bearing polypeptides and proteins on attenuated total reflecting (ATR) sensor surfaces for the detection of biomolecular interactions by FTIR spectroscopy. Nitrilotriacetic acid (NTA) groups are covalently attached to self-assembled monolayers of either thioalkanes on gold films or mercaptosilanes on silicon dioxide films deposited on germanium internal reflection elements. Complex formation between Ni2+ ions and NTA groups activates the ATR sensor surface for the selective binding of polyhistidine sequences. This approach not only allows a stable and reversible immobilization of histidine-tagged peptides (His-peptides) but also simultaneously allows the direct in situ quantification of surface-adsorbed molecules from their specific FTIR spectral bands. The surface concentrations of both NTA and His-peptide on silanized surfaces were determined to be 1.1 and 0.4 molecules nm-2, respectively, which means that the surface is densely covered. A comparison of experimental FTIR spectra with simulated spectra reveals a surface-enhancement effect of one order of magnitude for the gold surfaces. With the presented sensor surfaces, new ways are opened up to investigate, in situ and with high sensitivity and reproducibility, protein-ligand, protein-protein, protein-DNA interactions, and DNA hybridization by ATR-FTIR spectroscopy.

Stacks of close to 100 phospholipid bilayers fully accessible to proteins: An ATR–FTIR-based chemometric analysis on hydrated phospholipid films

A novel method for measuring aqueous solutions of proteins having high affinity for specific membrane components has been developed from attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectra. The method was based on the use of a germanium internal reflection element (IRE) which surface was covered with a PE–biotin film. In order to investigate the potentialities of this approach, streptavidin in aqueous solutions was recirculated continuously in a flow-trough mode on the hydrated phospholipid film. Partial least squares (PLS) and principal component regression (PCR) were used and compared for establishing a multivariate calibration model for streptavidin concentrations ranging from 50 to 500 mg l −1. The best agreement between the known and predicted concentrations of streptavidin by PLS and PCR was obtained when both methods were optimized by selecting the spectral regions having the highest correlation with concentration data. PLS revealed more accurate results than PCR with a standard error of prediction (SEP) of 18.56 mg l −1 (7%). The streptavidin amount effectively bound to the PE–biotin film was estimated separately via a univariate regression between ATR–FTIR absorbance and concentration data representing different protein:phospholipid ratios. The results demonstrated that the protein was capable of diffusing and attaining all of the available sites in the multilayer PE–biotin matrix. Such a phospholipid film-based measurement method is a promising tool for developing new sensing methods for analyzing biomolecules in aqueous solutions.

Attenuated Total Internal Reflection Infrared Mapping Microspectroscopy Using an Imaging Microscope

Attenuated total internal reflection (ATR) infrared mapping microspectroscopy using an infrared microscope and a focal plane array is investigated and reported. The study demonstrates the advantages of conducting ATR microspectroscopy using a focal plane array detector. These benefits include the rapid acquisition of molecular specific images, ease of sample preparation, and increased spatial resolution. An experimental determination of the spatial resolution found that the combined system operates very close to the diffraction limit, and a 4 magnification factor associated with the germanium internal reflection element was realized. Experiments conducted on several polymer samples and a biological sample demonstrate the future viability of the method.

Investigation of Polysaccharide Adsorption on Protein Conditioning Films by Attenuated Total Reflection Infrared Spectrometry: II. Thin Copper Films

The study of microorganisms at the aqueous/metal interface is of great interest as their presence is often associated with surface deterioration or corrosion. Surfaces submerged in aquatic environments rapidly become fouled with organic macromolecules, such as proteins and/or glycoproteins. Bacteria adhering to this conditioning film typically produce extracellular polysaccharides that anchor the cells to the substrate. In a previous paper, the kinetics of polysaccharide adsorption and desorption on protein conditioning films formed on bare germanium internal reflection elements (IREs) were investigated in an effort to gain a better understanding of the fouling process. This work has been extended to the study of adsorption phenomena at an aqueous/copper interface. Alginic acid and dextran were exposed to protein-conditioned and untreated copper films. In the absence of a protein biofilm, greater erosion of the Cu film was observed with flowing saline than with a solution of alginic acid in saline, and more Cu was removed at pH 4.8 than at pH 7.0. The neutral polysaccharide was less corrosive than alginic acid. The presence of a film of bovine serum albumin (13.5 nm) conditioning film did not shield the Cu film from the corrosive effects of either polysaccharide. In all experiments, as Cu slowly eroded from the surface of the IRE, metal islands formed leading to the observation of surface-enhanced infrared absorption (SEIRA). The intensity of the C–O stretching band of adsorbed dextran on Cu islands was over an order of magnitude greater than would be observed with a uniform Cu film of the same thickness. Enhancement of the amide II band of BSA was also observed. In general, the effect of SEIRA complicated spectral processing and interpretation and thus interfered with the determination of surface coverage and polysaccharide adsorption/desorption kinetics on protein conditioning films.

Membrane Helix Orientation from Linear Dichroism of Infrared Attenuated Total Reflection Spectra

Oriented multilamellar systems containing phospholipids and peptides have been formed on a germanium internal reflection element. Attenuated total reflection infrared spectra have been recorded and the linear dichroism of peptide amide I and amide II bands measured. Using peptides for which the orientation had been previously studied under similar experimental conditions by 15N solid-state nuclear magnetic resonance spectroscopy, important conclusions were drawn on the approach to be used to derive secondary structure orientation in a membrane from dichroic ratios. In particular, it is shown that the influence of the film thickness and refractive index on the orientation determination can be evaluated from the value of R ATRiso, i.e., the dichroic ratio of a dipole oriented at the magic angle or with isotropic mobility. A series of peptides was used to test the validity of our suggestions on various helix orientations in the membrane. These include magainin 2 and hydrophobic (hΦ20) model peptides, the transmembrane segment of glycophorin (GLY), and LAH 4, a designed peptide antibiotic that changes between a transmembrane and an in-plane orientation in a pH-dependent manner.

Theoretical determination of parameters for optimum surface specificity in overlayer attenuated-total-reflection infrared spectroscopy

We investigate the feasibility of overlayer attenuated-total-reflectance (O-ATR) infrared spectroscopy as a surface analytical tool for studying reactions and molecular properties of adsorbates at surfaces exposed to aqueous nonelectrolyte solutions. Through modeling an O-ATR system by assuming it to comprise three, four, or n phases of homogeneous refractive index, one can use an electric-field analysis to determine how the parameters of adsorption free energy, overlayer thickness, initial angle of incidence, and internal-reflection element refractive-index influence solvent-subtracted O-ATR infrared-absorption spectra. The theory behind such an analysis is explained, and the results of its application are presented for hypothetical O-ATR systems consisting of either a zinc selenide or a germanium internal-reflection element, an iron or hematite overlayer, an adsorbate layer, and a solution of methylene chloride in water.

FTIR internal reflection spectroscopy studies of the effect of pH on adsorption of oleate/oleic acid at the surface of a TiO 2 thin film deposited on a Ge single crystal

The adsorption of oleate/oleic acid from aqueous solutions at the surface of titanium dioxide was examined by Fourier transform infrared (FT-IR) spectroscopy using a germanium internal reflection element coated with a thin film of TiO 2. This thin film, with a thickness of 100–200 Å, was deposited on the surface of a germanium single crystal by rf dc magnetron reactive sputtering. It was found that significant adsorption of oleate/oleic acid from a 0.03 mM aqueous solution occurs at neutral and close-to-neutral pH, from about pH = 4.5 to pH = 8.5. The surface density vs. pH relationship obtained in this study is consistent with literature reports on the effect of pH on flotation recovery of rutile from oleic acid solutions.

Direct Observation of Self-Assembled Monolayers, Ion Complexation, and Protein Conformation at the Gold/Water Interface: An FTIR Spectroscopic Approach

A simple approach to the in situ measurement of infrared spectra of self-assembled monolayers (SAMs) on gold in an aqueous environment is described. A thin gold film (3−5 nm) on the surface of a germanium internal reflection element is used as a substrate for the self-assembly of a monolayer of a chelating thioalkane. High signal-to-noise spectra are obtained, allowing identification of the chemical groups present in the SAM. Complexation of ions by the SAM can be monitored, and the secondary conformation of his-tagged proteins bound to the SAM can be observed.

Studies of Techniques for Analysis of Photocopy Toners by IR

Abstract A study was undertaken to examine three measurement techniques for the analysis of photocopy toners by microscopical infrared spectrometry (IR) and to compare these techniques to studies previously done by Diffuse Reflectance (DR). Based on our preliminary studies, analysis of photocopy toners may be successfully performed by DR, microscopical Attenuated Total Reflectance (ATR) with a germanium Internal Reflection Element (IRE) or by microscopical Reflection-Absorption (R-A) techniques with a variety of reflecting media including mirrored slides, low emissivity glass, and aluminum foil. Selection of the analysis technique can be made based on equipment availability, budgetary constraints, ease of sample preparation, speed of analysis, and importance of the original photocopied document to determine if a mildly destructive technique can be used.