Interference spectroscopy

Figure 4. Reflectometric interference spectroscopy (RIFS) caused by constructive and destructive superposition of two partial beams being reflected at the two interfaces of a thin layer (300 nm - some pm), shift of the interference spectrum caused by a change in the optical thickness.

In the following, the application of these concepts is shown both for reffactometric and reflectometric measurements using Mach-Zehnder interferometers and reflectometric interference spectroscopy. 

Reflectometric interference spectroscopy can also be used to easily determine various interactions between analytes and polymer films27. A typical application is given in Figure 14 for a homologuous series of alcohols29. 

Figure 17. Structure affinity relationship measurement using reflectometric interference spectroscopy of atrazine versus an antibody in water. A variety of derivatives of triazines are measured at a number of concentrations to obtain affinity constants.

Because of the more simple and robust technique of reflectometric interference spectroscopy, more applications of this method will be given in following. 

Figure 19. Procedure of measuring reflectrometric interference spectroscopy in a parallelized setup. Instead of white light, the wavelength obtaineds from some filters are used, and the interference spectra is constructed based on these supporting wavelengths. For each wavelength, all the measurement spots are obtained simultaneously, the total time for one wavelength set is less than 10 seconds.

Mehlmann M., Garvin A., Steinwand M., Gauglitz G., Coupling of reflectometric interference spectroscopy with MALDI-MS, in preparation. 

Birkert O., Tunnemann R., Jung G., Gauglitz G., Label-Free Parallel Screening of Combinatorial Triazine Libraries Using Reflectometric Interference Spectroscopy, Anal Chem 2002 74 834. 

Birkert O., Gauglitz G., Development of an assay for label-free high-throughput screening of thrombin inhibitors by use of reflectometric interference spectroscopy, AnalBioanal Chem 2002 372 141-147. 

Sauer M., Brecht A., Charisse K., Stemmier I., Gauglitz G. and Bayer E., Interaction of Chemically Modified Antisense Oligonucleotides with Sense DNA A Label-Free Interaction Study with Reflectometric Interference Spectroscopy, Anal Chem 1999 71 2850. 

Reichl, D. Krage, R. Krumme, C. Gauglitz, G., Sensing of volatile organic compounds using a simplified reflectometric interference spectroscopy setup, Appl. Spectrosc. 2000, 54, 583 586... 

Low, M. J. D., Epstein, L. R., and Bond, A. C., Infrared spectra of methyldiboranes. The examination of unstable substances using multiple-scan interference spectroscopy, Chem. Comm., 226 (1967). 

In this section an overview of the numerous methods and principles for the discrimination of enantiomers is given. First, the interaction principles of the polymer-based methods adapted from chromatographic procedures are illustrated. The discrimination of enantiomers was achieved some decades ago by using different types of stationary materials, like cyclodextrins or polymer-bonded amide selectors. These stationary-phase materials have successfully been appointed for label-free optical sensing methods like surface plasmon resonance (SPR) or reflectometric interference spectroscopy (RIfS). Furthermore, various successful applications to optical spectroscopy of the well-established method of fluorescence measurements for the discrimination of enantiomers are described. 

Fig. 5 Relative reflectometric interference spectroscopy sensor signals (normalised with regard to the layer thickness without analyte gas) of two chiral sensors (S-sensor, grey line R-sensor, black) and an additional SE-30 sensor (points) upon exposure to mixtures of different enantiomeric composition (in percent) of N-TFA-Ala-OMe [18]...

A chemical sensor is a device that transforms chemical information into an analytically useful signal. Chemical sensors contain two basic functional units a receptor part and a transducer part. The receptor part is usually a sensitive layer, therefore a well founded knowledge about the mechanism of interaction of the analytes of interest and the selected sensitive layer has to be achieved. Various optical methods have been exploited in chemical sensors to transform the spectral information into useful signals which can be interpreted as chemical information about the analytes [1]. These are either reflectometric or refractometric methods. Optical sensors based on reflectometry are reflectometric interference spectroscopy (RIfS) [2] and ellipsometry [3,4], Evanescent field techniques, which are sensitive to changes in the refractive index, open a wide variety of optical detection principles [5] such as surface plasmon resonance spectroscopy (SPR) [6—8], Mach-Zehnder interferometer [9], Young interferometer [10], grating coupler [11] or resonant mirror [12] devices. All these optical... 

The interaction behaviour of the homologous alcohols methanol, ethanol and 1-propanol and the ultramicroporous polymer Makrolon was investigated by three different optical methods spectral ellipsometry, surface plasmon resonance and reflectometric interference spectroscopy. 

The interaction behaviour of five Makrolon layers of different thicknesses between 70 nm and 455 nm and the three homologous alcohols was investigated by reflecto-metric interference spectroscopy. In Fig. 5 the changes of the optical thickness of a 205 nm layer is plotted versus the concentrations of the three homologous alcohols. For methanol there is a relatively linear increase of the change in optical thickness. For the two greater analytes, the curves are more arcuated and the Henry-Langmuir-behaviour can be seen more clearly. 

In contrast to SPFS, SPR, and SPDS are tools that can study biomolecular interactions without external labels. They share the same category of label-free biosensors with the reflectometry interference spectroscopy (RIfS) [46], waveguide spectroscopy [47], quartz crystal microbalance (QCM) [48], micro-cantilever sensors [49], etc. Although the label-free sensors cannot compete with SPFS in terms of sensitivity [11], they are however advantageous in avoiding any additional cost/time in labeling the molecules. In particular, the label-free detection concept eliminates undue detrimental effects originating from the labels that may interfere with the fundamental interaction. In this sense, it is worthwhile to develop and improve such sensors as instruments complementary to those ultra-sensitive sensors that require labels. 

Any quantum system can be associated to an I-frame thereby, internal and "external" (I-frame) quantum states can be determined or at least observed as done in astronomy. Probing (measuring) a quantum system breaks Hilbert space-time evolution thereby preparing a new quantum state. This latter can be used to detect the result due to probing. See Ref. [29] for an illustration. Gravitation is a prototype of classical effects. From neutron interference spectroscopy gravitation effects on quantum states are well documented. 

Total internal reflection fluorescence (TIRE) Reflectrometric interference spectroscopy (RIfS)... 

Fig. 5.15. Illustration of the basic principle of the reflectometric interference spectroscopy (RifS) biosensor. See text for details of the working principle.

Mehlmann, M., Garvin, A. M., Steinwand, M., Gauglitz, G. (2005). Reflectometric interference spectroscopy combined with MALDI-TOF mass spectrometry to determine quantitative and qualitative binding of mixtures of vancomycin derivatives. Anal. 

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