Kretschmann configuration

Fig. 4 The effect of proteins on cell adhesion, (a) Kretschmann configuration for SPR. (b) Reflectance (R) as a function of incident angle (9), before (black) and after (red) the adsorption of substances, (c) Left. Time course of SPR angle shift during exposure to culture medium supplemented with 2% FBS (solid line) and the fraction of adherent cells determined by TIRFM (circles) on NH2-SAM. The dashed line is a manual fit to the symbols, included simply as a guide [42]. Right The concentrations of serum proteins in FBS...

The immune biosensor analysis was carried out in the SPR-4 M device produced by the Institute of Physics of Semiconductors of the Ukrainian National Academy of Sciences. SPR spectroscopy was carried out in the Kretschmann configuration using He-Ne laser ( i=632.8 nm), goniometer (G-5 M), glass prism (the angle at the basis 68°) and photodiode (FD 263). The optical contact between the prism and the metallic layer was achieved by the application of polyphenyl ether (refractive index n= 1.62). 

Fig. 2 Surface plasmon resonance device in the Kretschmann configuration, so is the refractive index of prism, ei is the refractive index of thin metal film (usually Au or Ag), 62 is the refractive index of air, and 0 represents the critical angle...

Combination of Surface Plasmon Resonance (SPR) and Optical Waveguide Spectroscopy (OWS) was used for the simultaneous determination of refractive index and film thickness of the hydrogel layers in the Kretschmann configuration [24], The resulting angle scans from the SPR instrument were fit to Fresnel calculations and different layers were represented using a simple box model. A detailed description of this process has been published previously [18]. 

Fig. 1 Kretschmann configuration in SPR depicting the conversion of energy from light waves to surface plasmons via a gold/dielectric interface...

Usually, there are two ways of optical excitation to achieve the resonant condition total refiection in prism-coupler structures [12] and diffraction at diffraction gratings [13]. The most commonly used is the first one due to its simplicity, and it is called the Kretschmann configuration, already shown in Fig. 5.5a. 

Fig. 5.6. An SPR experimental set-up based on the Kretschmann configuration. A glass hemicylinder is covered with a glass slide coated with gold (45 nm), using a matching oil and then exposed to the sample solutions using a flow cell with two channels. The reflected intensities of both channels are measured in a photodiode. (More details in the flgure itself).

In the experimental study of surface excitons various optical methods have been used successfully, including the methods of linear and nonlinear spectroscopy of surface polaritons. A particularly large body of information has been obtained by the method of attenuated total reflection of light (ATR), introduced by Otto (1 2) (Fig. 12.1) to study surface plasmons in metals. Later the useful modification of ATR method also was introduced by Kretschmann (3) (the so-called Kretschmann configuration, see Fig. 12.2). The different modification of ATR method has opened the way to an important development in the optical studies of surface waves and later was used by numerous authors for investigations of various surface excitations. 

FlG. 12.2. Kretschmann configuration for investigation of surface wave at interface of metal (silver, in this case) and coating. 

Fig. 5.5. Kretschmann configuration of SPR gas sensing method. The graph indicates a real-time measurement of intensity at a given wavelength and angle of reflected light...

Fig. 5.150. Electrochemical cell for SPR measurements based on the Kretschmann configuration...

In general, the system comprises the light source, detector, optical system (mostly prism), and a sensor chip (mostly thin gold film) (Fig. 4.23). The sensor chip, depending on the method, can stay in direct contact with the prism surface (Kretschmann configuration) or close to the surface (Otto configuration). 

Over recent years, internal reflectance infrared studies have tended to concentrate on the study of relatively thick films of conducting polymers or layers, (see, for example, the work of Pham and coworkers [49, 50], or Kvarn-strom, Nauer, Neugebauer and coworkers [51-54]) in which sensitivity was not a particular problem, or on the semiconductor-electrolyte interface, (see the work of Chazalviel and coworkers [35, 40, 41]), in which the SPP excitation approach is not appropriate. However, interest has focused again on this phenomenon with the surface-enhanced infrared absorption spectroscopy (SEIRAS) studies of Osawa and coworkers [19, 26, 27, 46, 55, 56], who have combined the application of the Kretschmann configuration with step-scan FTIR spectroscopy to study fast, reversible electrochemical processes on timescales down to microseconds [26, 46, 57-60]. 

Melendres and Hahn [173] have extended the vertical spatial resolution of in situ infrared spectroscopy by employing synchrotron radiation in the far-infrared region of the spectrum, (synchrotron far infrared spectroscopy, SFIRS), to study metal-adsorbate bonds. The authors exploited the Kretschmann configuration to improve the sensitivity of the technique, and studied the adsorption of Cl and Br at the thin Au film working electrode. They observed bands near 263 and 187 cm for the Au—Cl and Au—Br stretches, respectively, in good agreement with the SERS data of Gao and Weaver [174]. 

More complicated dependences are observed when two layers are located on the surface of the ATR element. The optical properties of a hemicylin-drical IRE-thin (d < 50 nm) metal hhn-hlm system, called the Kretschmann configuration [84] (Fig. 2.36a), were actively investigated in the seventies and eighties (see, e.g.. Ref. [85]) regarding the possibility of SEW excitation at the metal-outer layer interface. However, even without exploiting this and surface-enhanced infrared absorption (SEIRA) (Section 3.9.4) effects, optical enhancement may be achieved in the ATR spectrum of a layer deposited on metal. Because of this, the Kretschmann configuration has found wide application in the investigation of nanolayers located on the metal surfaces, especially at the metal-solution interface (Section 4.6.3). 

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