We describe an optical technique for detecting and monitoring antibody-antigen reactions at a solid-liquid interface. The antibody is covalently immobilized onto the surface of either a planar (microscope slide) or cylindrical (fibre optic) waveguide made of fused quartz. The reaction of immobilized antibody with antigen in solution is detected through use of the evanescent wave component of a light beam, which has a characteristic depth of penetration of a fraction of a wavelength into the aqueous phase, thus optically interacting primarily with substances bound (or located very close) to the interface and only minimally with the bulk solution. This resulting in-situ spatial separation of the antibody-bound from free antigen precludes a formal separation step and allows the reaction to be monitored kinetically. An immunoassay for methotrexate by absorption spectrometry achieved a detection limit of about 270 nmol/L; binding of methotrexate by immobilized antibody was monitored by the decrease in transmittance at 310 nm. A two-site immunofluorometric assay for human IgG could detect as little as 30 nmol/L; binding of fluorescein-labeled antibody was monitored by the increase in signal above 520 nm (lambda ex = 495 nm). With both immunoassays the signal-generating phase was monitored kinetically and was completed within 15 min.
New grades of sintered (polycrystalline) corundum ceramics have been shown to exhibit a ballistic shielding power close to SiC/B 4 C composites when manufactured with a grain size of about 500 nm. It is demonstrated here that these Al 2 O 3 ceramics become WUDQVSDUHQW when their residual porosity is decreased to less than 0.05 %. Specifically, in the IR range between about 2 and 6 µm their transmissivity equals that of sapphire approaching the upper theoretical limit for wavelengths of 2.5-4.5 µm. This opens the way to new possible applications such as IR domes. These optically and mechanically homogeneous ceramics can be manufactured with a wall thickness up to 15 mm by a wet casting approach. The technology enables the manufacture of complex hollow spheres which after sintering are transparent in visible light without polishing. .H\ZRUGV IR transparent domes/windows, transparent ceramics, sintered ceramics, alumina, corundum, sapphire, Al 2 O 3 ,QWURGXFWLRQ Sapphire domes are known as commercially available IR-transparent components of high strength. Their transparency is high through the visible and up to the IR range. However, sapphire domes not only are expensive because of difficult growth and polishing procedures, their fracture toughness (K Ic < 3 MPa√m for most orientations) and macrohardness (HV10 < 18.5 GPa) is lower than obtained with advanced sintered polycrystals which combine a sub-µm microstructure with a high relative density > 99.5 % (resulting in values of K Ic ≈ 3.5 MPa√m, HV10 > 20 GPa 1 , 4-pt-bening strength 700 MPa 2 ). Among these properties it is first of all the extreme brittleness of sapphire (Fig. 1) which could limit its use for future systems currently under development (applications with high thermomechanical loads beyond those tolerated by existing sapphire domes and possibly associated with highly dynamic micro-or macro-impacts on the surfaces). Figure 1: High brittleness of sapphire demonstrated by indentation cracking compared with sintered polycrystalline Al 2 O 3 (testing load 10 kgf). Different magnifications show the wide extension of cracks in sapphire compared with the large SODVWLF deformation RI WKH PLFURVWUXFWXUH in the sintered material (fine-grained polycrystal [grain size 1 µm]); an as-sintered (not polished) surface was indented in order to display the difference between the smoothed surface within and the grained microstructure outside the indent.
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