Attenuated internal reflectance spectroscopy

Due to the fundamental importance of the adsorbed protein film, many methods have been used to characterize its nature. These methods include ellipsometry (3,A), Fourier transform infrared spectroscopy (FTIR) (5,6), multiple attenuated internal reflection spectroscopy (MAIR) (7,8) immunological labeling techniques (9), radioisotope labeled binding studies (j ), calorimetric adsorption studies (jj ), circular dichroism spectroscopy (CDS) (12), electrophoresis (j ), electron spectroscopy for chemical analysis (ESCA) (1 ), scanning electron microscopy (SEM) (15,16,9), and transmission electron microscopy (TEM) (17-19). 

In materials investigations surface-sensitive techniques are of special interest. The major contribution of infrared spectroscopy to this field is internal reflection spectroscopy (IRS), often called the "attenuated total reflection" (ATR) technique. To describe theory and principle, electromagnetic wave theory must be apphed [33]. 

Many compounds exhibit near-IR and mid-IR absorption. By using IR transparent optical fibers, detection of an absorption band in the IR region is possible for optical sensing. Both direct sensing using the absorption property of the analyte or indicator sensing are widely exploited. Most mid-IR sensing schemes are based on the principles of internal reflection spectroscopy, or the attenuated total reflection (ATR) [3,14-21],... 

A variety of eell designs for internal reflection or attenuated total reflection spectroscopy have been reported, demonstrating the flexibility of the technique. In the following, we describe only a few examples in some detail. 

In internal reflection spectroscopy (IRS) the sample is in optical contact with another material (e.g. a prism). The prism is optically denser than the sample. The incoming light forms a standing wave pattern at the interface within the dense prism medium, whereas in the rare medium the amplitude of the electric field falls off exponentially with the distance from the phase boundary. If the rare medium exhibits absorption, the penetrating wave becomes attenuated, so the reflectance can be written... 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

Fluctuations in the dielectric properties near the interface lead to scattering of the EW as well as changes in the intensity of the internally reflected wave. Changes in optical absorption can be detected in the internally reflected beam and lead to the well-known technique of attenuated total reflectance spectroscopy (ATR). Changes in the real part of the dielectric function lead to scattering, which is the main topic of this review. Polarization of the incident beam is important. For s polarization (electric field vector perpendicular to the plane defined by the incident and reflected beams or parallel to the interface), there is no electric held component normal to the interface, and the electric field is continuous across the interface. For p polarization (electric field vector parallel to the plane defined by the incident and reflected beams), there is a finite electric field component normal to the interface. In macroscopic electrodynamics this normal component is discontinuous across the interface, and the discontinuity is related to the induced surface charge at the interface. Such discontinuity is unphysical on the molecular scale [4], and the macroscopic formalism may have to be re-examined if it is applied to molecules within a few A of the interface. 

The second case refers to the so-called Internal Reflection Spectroscopy, that is used in the so-called Attenuated Multiple Total Internal Reflection technique... 

The only piece of experimental evidence for the orientation of apoA-I helices on DMPC discoidal complexes has come from the use of polarized attenuated total reflection infrared (ATR-IR) spectroscopy (Brasseur et al. (1990 Wald et al., 1990). Although internal reflection spectroscopy is not new (Harrick, 1967), its combination with polarized IR measurements of oriented biological membranes is a more recent application, which allows the spectrum to be taken in the presence of water. The technique has been used most frequently to study the orientation of lipid functional groups relative to the membrane plane in pure lipid bilayers (Fringeli and Gunthard, 1981 Holmgre et al., 1987 Okamura et al., 1990 Hubner and Mantsch, 1991), but has also been applied to studies of... 

Another approach, internal reflection spectroscopy (IRS) or attenuated total reflectance (ATR) spectroscopy, takes advantage of the total reflection observed when a light beam is directed to the back of the OTE at an angle greater than the critical angle. Since the reflection takes place at the electrode-solution interface, the light beam is attenuated only by molecules close to the electrode surface. The penetration depth is about 1000 A in a typical experiment. Because of this very small effective cell length, the electrode is most frequently used in a multiple reflection mode [Fig. 44(b)]. 

Specific spectroscopic techniques are used for the analysis of polymer surface (or more correctly of a thin layer at the surface of the polymer). They are applied for the study of surface coatings, surface oxidation, surface morphology, etc. These techniques are typically done by irradiating the polymer surface with photons, electrons or ions that penetrate only a thin layer of the polymer surface. This irradiation is followed by the absorption of a part of the incident radiation or by the emission of specific radiation, which is subsequently analyzed providing information about the polymer surface. One of the most common techniques used for the study of polymer surfaces is attenuated total reflectance in IR (ATR), also known as internal reflection spectroscopy. Other techniques include scanning electron microscopy, photoacoustic spectroscopy, electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), etc. 

Internal reflection spectroscopy (2), also known as attenuated total reflectance (ATR), is a versatile, nondestructive technique for obtaining the IR spectrum of the surface of a material or the spectrum of materials either too thick or too strongly absorbing to be analyzed by standard transmission spectroscopy. The technique goes back to Newton who, in studies of the total reflection light at the interface between two media of different retractive indices, discovered that an evanescent wave in the less dense medium extends beyond the reflecting interface. Infrared spectra can conveniently be obtained by measuring the interaction of the evanescent wave with the external less dense medium. 

Internal-reflection spectroscopy (IRS), also known as attenuated total-reflection (ATR) spectroscopy, is one of the most widely used techniques to generate spectra from intensely absorbing samples. The principle of operation is shown in Figure 3.13(b). 

Another technique that is important for optical immunosensor development is internal or attenuated total reflection spectroscopy (Fig. 126). A waveguide (slide or fiber) having a high refractive index is coated with a layer of immobilized antibody. The incident light... 

The polymer properties in thin films are then compared with the bulk as measured by FTIR attenuated total reflection spectroscopy (ATR). A modest refractive index of the internal reflection element (IRE made of ZnSe, n=2.43 at 2000 cm ) and an incident angle of 65° - still low but well above the critical angle of total reflection - are chosen for the p-polarized light in order to obtain an information depth of several microns. Hence, the ATR spectra provide the bulk properties of the polymer sample. 

Another variant of IR spectroscopic technique is known as Fourier Transform IR Attenuated Total Reflection Spectroscopy (ATR FT-IR) has been described by Poston et al. [123] to study adsorbates at the silica-solution interface. The authors reported the preparation of ZnSe internal-reflection elements coated with a porous silica layer of ca. 700 nm thick. They studied the adsorption of ethylacetate from n-heptane solutions. This technique allows the determination of IR spectra in-situ and its dependence on the solution concentration. They found a nonlinear adsorption isotherm of ethylacetate on... 

Internal reflectance Spectroscopy (IRS) date back to the initial work of Jacques fahrenfort and N.J.Harrrick [1, 2] that independently devised the theories of IRS spectroscopy and suggested a wide range of applications. Internal reflection Spectroscopy is often termed as attenuated total reflection (ATR) spectroscopy. ATR became a popular spectroscopic technique in the early l%0s. 

Aqueous solutions have traditionally posed a problem for IR spectroscopy due to the fact that water is a strong absorber of IR radiation. This difficulty, for aqueous solutions and other strongly absorbing liquid and solid samples, can be overcome by using attenuated total reflection spectroscopy. In this technique, the phenomenon of total internal reflection is used in such a way that it is only the evanescent wave associated with total internal reflection that enters the sample. The evanescent wave penetrates the sample very short distances only, hence the advantage for strongly absorbing species. 

Baier, R. E., and Zisman, W. A., Wettability and multiple attenuated internal reflection infrared spectroscopy of solvent-cast thin films of polyamides. Macromolecules, 3, 462-468 (1970). 

Figure 4.3 Theory of attenuated total internal reflectance spectroscopy. (Source Author s own files)...

S. Tsukahara and H. Watarai, Transient attenuated total internal reflection spectroscopy to measure the relaxation kinetics of triplet state of tetra(N-methylpyridinium-4-yl)porphine at liquid-liquid interface, Chem. Lett., 89-90 (1999). 

Internal reflection spectroscopy, also known as attenuated total reflectance (ATR) or multiple internal reflectance (MIR), is a versatile, nondestructive technique for obtaining the infrared spectrum of the surface of a material or the spectrum of materials either too thick or too strongly absorbing to be analyzed by standard transmission spectroscopy. 

Internal reflectance spectroscopy (IRS alternatively named attenuated total reflectance, ATR) is a quick and easy non-destructive sampling technique for obtaining the IR spectrum of a material s surface or of material which is either too thick, or strongly absorbing, to be analysed by more traditional transmission methods, cfr Chp. 1.2.1.4. Internal reflection techniques, which require close contact with an internal reflection element (IRE) are unsuitable for rapid screening of plastic materials. 

An important method called internal reflection spectroscopy (IRS) or attenuated total reflection (ATR) for obtaining the infrared spectra of solids or films has been described by Fahrenfort.Harrick has also discussed the theory in considerable detail. 

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