Receptor-based coatings

Microcantilever sensors can be operated in modes in which receptor-based coatings are not needed for example, deflagration of adsorbed energetic molecules can induce a measurable response [10]. Since cantilevers can be made extremely sensitive to temperature using bimaterial effect, calorimetric methods can be carried out on cantilevers with adsorbed molecules [11, 12], Exposing the temperature-sensitive cantilevers with adsorbed species to different infrared (IR) wavelengths in a sequential fashion creates mechanical signatures that mimic the IR absorption spectra of the analyte [13]. 

Based on well established silica chemistry, the surface of silica nanomaterials can be modified to introduce a variety of functionalizations [3, 11, 118]. The toxicity of surface-modified nanomaterials is largely determined by their surface functional groups. As an example, Kreuter reported that an apolipoprotein coating on silica nanoparticles aided their endocytosis in brain capillaries through the LDL-receptor [122-124]. Overall, silica nanomaterials are low-toxicity materials, although their toxicity can be altered by surface modifications. 

Surface immobilization of the capture molecules follows standard procedures that are commonly practiced in many biosensor applications and some are discussed in the previous section. Layers of carboxymethyl dextran. Protein A or Protein G, streptavidin-coated surface, or EDC [N-ethyl-N-(diethylaminopropyl) carbidimide]/NHS (N-hydroxysuccmimide)-based amine coupling through amide bond are used for protein (antibody, receptor, etc.) cross-linking. 

Fig. 16.14. Configuration of the M2 helices of the acetylcholine receptor in the closed and open states. The schematic representation is based on a comparison of the electron density map of the acetylcholine receptor in closed and open states. Only three of the five M2 helices are shown, a) Closed state the M2 helices are bent at the middle. The leucine residues point into the interior of the pore and prevent passage of ions, b) Open state the M2 helices are turned outwards at a tangent and the bulky leucine residues are removed from the center of the pore. Reorientation of the M2 helices causes a reorientation of polar amino adds that coat the interior of the pore. The polar amino acids (Ser and Thr residues) are oriented closer to the center of the pore and create a hydrophilic coating of the pore inner wall, which facilitates ion passage. According to Unwin,...

Weissleder et al. [84] first showed that the human transferrin receptor (hTfR) can be used to internalize MRI contrast agents. The hTfR regulates cellular uptake of iron from transferrin, a plasmatic iron transport protein [85], via a receptor mediated endocytosis mechanism. Thus, MION particles (dextran coated iron oxide) were oxidized with sodium periodate. Holotransferrin was added and the resulting Schiff base adduct was reduced with sodium cyanoborohydride to give transferrin labeled MIONs, Tf-MION (Scheme 3). 

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