Receptor layers

Accordingly, in Figure 8 sensitive layers can demonstrate either a higher reversibility or a higher selectivity. In combination with these properties, polymers usually show a high reversibility since they have poor selectivity and since they are relatively stable in contrast to biomolecular receptor layers where the selectivity and the sensitivity are high, but where the stability is rather poor as is reversibility. 

The value of dn/dC depends on the properties of the material, e.g., in case of proteins this coefficient is 0.188 ml/g35 and in case of glucose dissolved in water (used for calibration measurements as discussed later in this chapter) this coefficient is 0.069 ml/g36. In the second mode of operation, analytes bind to the sensor surface (e.g., mediated by a receptor layer). In this case a thin layer with thickness w and refractive index nw is formed by the adsorbed analytes. Because the value of nw (e.g., 1.45 for proteins) is usually different than the refractive index of the solution (e.g., 1.33 for water) that contains the analyte molecules, a phase change is induced. The average layer growth (Aw) on the sensor surface can be related to the mass change (Am) per surface area (A) ... 

In an immunosensor the core-cover interface of an optical waveguide structure is coated with a chemo-optical transducer receptor layer, which can selectively bind to specific analyte molecules present in the cover medium. The receptor-analyte reaction obeys the law of mass action, which states that the rate of a reaction is proportional to the concentration of the reactants. At equilibrium, the rate of formation of the receptor-analyte complex is equal to the rate of breaking, and the equilibrium constant, K. can be written as... 

Equations (10.14) and (10.8) can be used for estimation of the thickness and mass coverage of the receptor adsorbed to the sensor surface and of the analyte layer bound to the receptor layer. 

Panasyuk TL, Mirsky VM, Piletsky SA, Wolfheis OS. Electropolymerized molecularly imprinted polymers as receptor layers in a capacitive chemical sensor. Anal Chem... 

Autoradiographic studies have shown a laminar distribution of D2 receptors in register with Lf receptors layer with high density of one receptor subtype have low density of the other. The D2 receptor mRNA, on the other hand, was found in the pyramidal cell layer of the Ammon s horn (the CA1, CA2 and CA3 fields) and in the granule cells of the dentate gyrus (Mansour et al., 1990). A mismatch between DA innervation and D2 receptors was observed in the hippocampus (Mansour et al., 1990 Kohler et al., 1991). 

Fig. 4 A TH labeled (dopaminergic) amacrine cell of the rat retina. Note that the receptor layer is on the top and the faintly visible ganglion cell layer is on the bottom (from Mytileneou and Bodis-WoUner, Department of Neurology, The Mt. Sinai School of Medicine, around 1978 unpublished data)...

Fig. 5.2. (a) Evanescent field of the fundamental propagation mode in an optical waveguide, (b) Interaction of the evanescent wave with a biomolecular reaction for sensing purposes. The adsorption of the receptor layer and the recognition process produces a change of the effective refractive index of the waveguide inside the evanescent field and this change is quantitatively related with the concentration of the analyte to be measured. 

Fig. 5.13. The resonant mirror device. The light from the soiuce is coupled through a prism Emd is totally reflected at the interface with the low refractive index layer, generating an evanescent field which couples light into the high refractive index waveguide layer The light transmitted through the waveguide also generates a evanescent field which interacts with the receptor layer.

The commercial sensors BIACORE [37] and lAsys [65] offer a variety of advanced surface chemistries for attachment of the different receptor layers as can be seen in Table 5.4. 

More reproducible and stable methods for immobilization of the receptor layers are also needed. Self-assembled methods at the nanometer scale, allowing stable and ordered receptor binding, must be further developed. 

Panasyuk, T. L. Mirsky, V. M. Piletsky, S. A. Wolfbeis, O. S. Electropolymerizedmolecularly imprinted polymers as receptor layers in capacitive chemical sensors. Anal. Chem. 1999, 71 (20), 4609-4613... 

The receptor layer comprising the outer and the inner segments of the photoreceptor cells. 

Figure 10.17. Comparison of sensor signals of the three cyclopeptide receptor layers sensitive for amino acids in buffer-free neutral water [97].

The working principle of the family of biosensors based on nanomechanical transducers, and specifically on microcantilevers, involves the translation of biochemical reactions into a mechanical movement in the nanometer range. In microcantilever sensors, the biochemical receptor layer is directly in contact with one of the cantilever surface. The biomolecular recognition process between the receptor layer and its corresponding analyte induce... 

In a later publication the group incorporated their sensor in a flow system [117]. Detection of the HIV antibodies was also carried out in serum samples. Dilution of the serum in buffer ensured the suppression of nonspecific effects and that negligible viscosity effects were observed. As long as the antibody concentration in the serum was not too high and didn t saturate the receptor layer on the crystal surface, several assays could be performed on... 

Fig. 8 Idealised model of acoustic attenuation. A Diagrammatic representation of a thickness shear mode bulk acoustic wave resonator, coated with a rigid metal adhesion and electrode layer, a rigid chemical linker layer, a finite viscoelastic antibody receptor layer, a second adherent finite viscoelastic analyte layer, and finally a Newtonian liquid. B An idealised model of acoustic attenuation from bulk quartz through the above layers of varying viscosity, density, and shear modulus...

A functionalized sensor with structure as shown in Fig. 7.15b had higher sensitivity and response speed. In this functionalized OFET sensor, 15 nm of 6PTTP6 and HO6OPT semiconductor blend, serving as a functionalized receptor layer, was coevaporated on top of a 35 nm 6PTTP6 film. 

The center response of bipolar cells results from direct contact with the receptors. The surround response is supplied by the horizontal cells, which run parallel to the surface of the retina between the receptor layer and the bipolar layer, allowing the surrounding area to oppose the influence of the center. The amacrine cells, a final cell type, also run parallel to the surface but in a different layer, between the bipolar cells and the ganghon cells, and are possibly involved in the detection of motion. 

Scheme 2 Functions of MIP films by various responses to specific template recognition in a receptor layer (i) direct or indirect monitoring of template binding (ii) monitoring of template binding via local changes of the MIP site (iii) monitoring of template binding via induced changes of the entire MIP film and (iv) coupled template binding and membrane permeation selectivity.

---