Reflectometric interference spectroscopy

The reflectometric interference spectroscopy (RIfS) is a physical method based on the interference of white light in thin layers, is based. This method is used in practice to study molecular interactions. The basic measuring principle corresponds to the Fabry-Pérot interferometer .

realization

Left: Schematic representation of the beam path in the case of multiple reflections at the boundary layers. Right: Schematic representation of the resulting interference spectrum

White light is radiated vertically onto a multilayer system. This consists of a silicon dioxide (SiO ₂ -), a high-index tantalum pentoxide (Ta ₂ O ₅ -) and another silicon dioxide layer that can be chemically modified. At each phase boundary, partial beams of white light are reflected and transmitted in refracted fashion. The reflected partial beams are superimposed to form an interference spectrum, which is detected using a diode line spectrometer. The uppermost SiO ₂ layer is changed by chemical modification so that it can interact with target molecules. This interaction causes a change in the physical layer thickness and the refractive index of this layer. The product of the two is defined as the optical film thickness: . The change in the optical layer thickness leads to a modulation of the interference spectrum. If one observes the change in the interference spectrum over time, it is possible to follow the binding behavior of the target molecules. ${\ displaystyle d}$ ${\ displaystyle n}$ ${\ displaystyle n \ cdot d}$

application

Schematic representation of a binding curve

RIfS is mainly used as a detection method in chemo- and biosensors .

Chemosensors are particularly suitable for measurements under difficult conditions and in the gas phase. Polymers which do not measure selectively are used as sensitive layers, which sort the analytes either on the basis of their size (so-called molecular sieve effect in microporous polymers) or on the basis of different polarities (e.g. functionalized polydimethylsiloxanes ). In the case of non-selective measurements, a sum signal from several analytes is measured in RIfS , so that multivariate data analyzes such as neural networks must be used for quantification . However, specifically measuring polymers, the so-called molecularly imprinted polymers (MIPs), which provide artificial recognition structures, can also be used.

In the field of biosensors, polymers such as polyethylene glycols or dextrans are applied to the layer system and recognition structures for biomolecules are immobilized on it. In principle, all substance classes can be used as recognition structures (proteins such as antibodies , DNA / RNA such as aptamers , small organic molecules such as estrone , but also lipids such as phospholipid membranes).

The method makes it possible to observe time-resolved interactions between the binding partners without having to resort to fluorescence or radioactivity markings. Like surface plasmon resonance spectroscopy (SPRS), it is a label-free technique. With monochromatic light, reflectometry on thin layers is referred to as single-wavelength reflectometry .

Web links

Barolo.ipc.uni-tuebingen.de

literature

G. Gauglitz, A. Brecht, G. Kraus, W. Mahm: Chemical and biochemical sensors based on interferometry at thin (multi-) layers . In: Sensors and Actuators B: Chemical . tape 11 , no. 1-3 , 1993, pp. 21-27 , doi : 10.1016 / 0925-4005 (93) 85234-2 .
Alexander Jung: DNA chip technology . In: Analytical and Bioanalytical Chemistry . tape 372 , no. 1 , 2002, p. 41-42 , doi : 10.1007 / s00216-001-1161-2 .
F. Gesellchen, B. Zimmermann, F. W Herberg: Direct optical detection of protein-ligand interactions . In: Methods Mol Biol . tape 305 , 2005, pp. 17-46 , doi : 10.1385 / 1-59259-912-5: 017 .
Thomas Nagel, Eva Ehrentreich-Förster, Mahavir Singh, Katrin Schmitt, Albrecht Brandenburg, Alexander Berka, Frank F. Bier: Direct detection of tuberculosis infection in blood serum using three optical label-free approaches . In: Sensors and Actuators B: Chemical . tape 129 , no. 2 , 2008, p. 934-940 , doi : 10.1016 / j.snb.2007.10.009 .
Peter Fechner, Florian Pröll, Mats Carlquist, Günther Proll: An advanced biosensor for the prediction of estrogenic effects of endocrine-disrupting chemicals on the estrogen receptor alpha . In: Analytical and Bioanalytical Chemistry . tape 393 , no. 6-7 , 2008, pp. 1579-1585 , doi : 10.1007 / s00216-008-2480-3 .