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A multichannel fluorometer is proposed for analysis of biochemical reactions. The sensor is based on the luminescence generation in the evanescent field of a totally reflected laser beam. For transduction, multiple reflection elements are used. Multichannel operation is realized, including the possibility of applying different solutions to each channel at the same time. First experimental results, obtained with fluorescein or Cy5 as labels in a model hybridization assay, demonstrate the applicability and allow the detection of 3-10 fmol injected fluorescently labeled oligonucleotide.

The reflection grating coupler for direct affinity sensing is characterized in detail. The performance of this device and its potential in affinity sensing application are investigated with two affinity-based systems: A self-assembling protein-multilayer system based on avidin-biotin interaction was used to compare the response of the device with theoretical expectations. The analytical performance was characterized by a pesticide immunoassay carried out in an indirect test format with a covalently immobilized triazine derivative. Experimentally determined parameters were in good agreement with model calculations. During the binding of 12 protein monolayers at the surface, the change in effective refractive index Dn(eff) detected for a single layer decreased from approximately 8 x 10(-4) to less than 4 x10(-5) by more than 95%, indicating a filling of the evanescent field. By comparison with bulk refractive-index measurements, a refractive index n(D) approximately 1.38 of the protein multilayer was estimated. Fitting of the model gave a refractive index n(D) = 1.377 of the protein multilayer and an average thickness of 11 nm for a single protein layer. An average noise of Dn(eff) = 8.5 x 10(-7) was detected, corresponding to approximately 1% of the maximum response for a protein monolayer. At a triazine derivative attached to the surface through dextran-based surface chemistry, a maximum antibody loading that corresponds to an Dn(eff) of 1.5 x 10(-3) was observed. In an indirect immunoassay of the herbicide simazine, a detection limit of 0.25 mug/1 of simazine was reached with polyclonal Fab fragments in a concentration of 1 mug/ml.

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Deep electron traps have been studied by means of deep level transient spectroscopy in n-type nominally undoped and intentionally Te-doped AlxGa1−xAs epitaxial layers which were grown by vapor phase epitaxy from organometallic compounds (OMVPE). Three main deep electron levels are present in undoped material: a trap with an activation energy of 0.8 eV, which is also found in GaAs grown by conventional VPE, and two levels specific to OMVPE with activation energies of 0.32 and 0.38 eV, respectively. The concentration of the 0.8 eV level is found to be independent of the aluminum content x, supporting the assumption that it is not related to substitutional oxygen. The other levels, however, exhibit a very strong dependence of concentration on the composition, varying by four orders of magnitude in the range of 0⩽x⩽0.35. In Te-doped samples, a level with an activation energy of 0.23 eV has been identified, which is thought to be related to an IR emission found in photoluminescence in OMVPE as well as in liquid phase epitaxial material.