Signal-responsive materials

Pita M, Minko S, Katz E. Enz3fme-based logic systems and their applications for novel multi-signal-responsive materials. J Mater Set Mater Med 2009 20 457-462. 

The field that generates these eddy currents is, by its nature, anisotropic, i e the eddy current signal response is directionally dependent on probe orientation. This can be used advantageously if one bears in mind that the corroded material one aims to detect usually displays random peaks and valleys, while man-made edges have a definite orientation. 

Different materials for the hydrophobic membrane in which the receptor is incorporated, have been investigated. Polysiloxanes that have the required glass transition temperature and dielectric constant provide a stable chemical system that transduces the complexation of cationic species into electronic signals. The material properties can be optimized by copolymerization of three building blocks viz. dimethyl-, (3-cyanopropyl)methyl-, and methacryloxypropylmethyl siloxane. CHEMFETs made with this terpolymer have fast response times (<. 1 sec.). With valinomycin and hemispherands (2) and (3) linear responses to changing K+ concentrations are obtained in the range 10"5 - 1.0M (55-58 mV/decade) in a solution of 0.1M NaCl. Similar devices specific for Na+ and Ca2+ have been obtained with other ionophores. 

Fig. 3 Double-antibody sandwich technique. The capturing antibody (Abl) is immobilized onto the solid phase. The analyte from the sample is captured by forming Abl-Ag immunocomplex. After washing off the extraneous materials from the sample, the reporting antibody (Ab2, which has an enzyme label in this illustration) is introduced. The double-antibody sandwich is formed Abl-Ag-Ab2E. Compounds not recognized by both Abl and Ab2 will be washed away. A chromogenic substrate is added to produce the product for detection. The occupied Ab2 by the Ag is measured this is an excess-reagent assay. As the sample analyte concentration increases, the signal responses increases proportionally.

Pull system In production, replenishment only when items are taken for use as a result of a pull signal. For material control, an issue of material is made only in response to a pull signal from a using entity. Similarly, in distribution, a pull signal comes from the downstream warehouses close to the end-user. (Adapted from APICS Dictionary, 10th edition)... 

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