Michael Kumpf

Total internal reflectance fluorescence (TIRF) biosensor for environmental monitoring of testosterone with commercially available immunochemistry: antibody characterization, assay development and real sample measurements.

Nowadays, little technology exists that can monitor various water sources quickly and at a reasonable cost. The ultra-sensitive, fully automated and robust biosensor River Analyser (RIANA) is capable of detecting multiple organic targets rapidly and simultaneously at a heterogeneous assay format (solid phase: bulk optical glass transducers). Commercialization of such a biosensor requires the availability of commercial high-affinity recognition elements (e.g. antibodies) and suitable commercial haptens (modified target molecules) for surface chemistry. Therfore, testosterone was chosen as model analyte, which is also a task of common analytical methods like gas chromatography-mass spectrometry (GC-MS), because they have to struggle with detecting sub-nanogram per liter levels in environmental samples. The reflectometric interference spectroscopy (RIfS) was used to characterize the commercially available immunochemistry resulting in a high-affinity constant of 2.6+/-0.3 x 10(9)mol(-1) for the unlabeled antibody. After the labeling procedure, necessary for the TIRF-based biosensor, a mean affinity constant of 1.2 x 10(9)mol(-1) was calculated out of RIfS (1.4+/-0.4 x 10(9)mol(-1)) and TIRF (1.0+/-0.3 x 10(9)mol(-1)) measurements. Thereafter, the TIRF-based biosensor setup was used to determine the steroidal hormone testosterone at real world samples without sample pre-treatment or sample pre-concentration. Results are shown for rapid and ultra-sensitive analyses of testosterone in aqueous samples with at a remarkable limit of detection (LOD) of 0.2 ng L(-1). All real world samples, even those containing testosterone in the sub-nanogram per liter range (e.g. 0.9 ng L(-1)), could be determined with recovery rates between 70 and 120%. Therefore, the sensor system is perfectly suited to serve as a low-cost system for surveillance and early warning in environmental analysis in addition to the common analytical methods. For the first time, commercially available immunochemistry was fully characterized using a label-free detection method (RIfS) and successfully incorporated into a TIRF-based biosensor setup (RIANA) for reliable sub-nanogram per liter detection of testosterone in aqueous environmental samples.

Biosensor for seven sulphonamides in drinking, ground, and surface water with difficult matrices

Abstract Environmental monitoring of antibiotics and other pharmaceuticals in real water samples with difficult matrices places high demands on chemical analysis. Biosensors have suitable characteristics like their efficiency in a fast, sensitive, and cost‐effective detection of pollutants. In this article, we present a recently developed immunoassay for seven sulphonamides (sulphadiazine, sulphamethoxazole, sulphadimidine, sulphamethizole, sulphadimethoxine, sulphathiazole, and sulphamethoxypyridazine) which can only be detected separately. For the simultaneous determination of multiple sulphonamides in the future we performed measurements with different combinations of binary mixtures. The results of the immunosensor were compared to a mathematical model which was developed in our group. Using an automated biosensor system it was possible for the first time to achieve limits of detection (LOD) below 10 ng L−1 and limits of quantification (LOQ) below 100 ng L−1 without sample pre‐concentration for these sulphonamides. Sulphonamide calibrations with different immobilised analyte derivatives were made in Milli‐Q water. Unstrained spiked and un‐spiked real water samples with complex matrices (drinking, ground, and surface water) were measured. In compliance with the Association of Analytical Communities (AOAC) International most recovery rates obtained were between 70% and 120%. The reproducibility was checked by measuring replica of each sample within independent repetitions. Robustness could be demonstrated by long‐term stability tests of the biosensor surface. These studies show that the biosensor used offers the necessary reproducibility, precision, and robustness required for an analytical method. The measuring data of the binary mixtures show a systematic error compared to the mathematical model at high concentrations of both sulphonamides, because the approximation uses only the standard calibration curves (data of the logistic fit function) as input data. It is also hard to adequately describe the cross‐reactivity and the behaviour of a mixture of polyclonal antibodies.

Dynamic Boundary Conditions and Boundary Control for the One-Dimensional Heat Equation

In this note we show how the theory of “one-sided coupled” operator matrices developed by K.-J. Engel [6-8] can be applied to boundary control problems. We illustrate the abstract results by considering the one-dimensional heat equation with dynamic boundary conditions and boundary control.