RESUMEN
Single-color reflectrometry is a sensitive and robust detection method in optical biosensor applications, for example for bioanalysis. It is based on the interference of reflected monochromatic radiation and is label free. We present a novel setup for single-color reflectometry based on the patented technology of Berner et al. from 2016. Tilting areas of micro-mirrors allow us to encode the optical reflection signal of an analyte and reference channel into a particular carrier frequency with the amplitude being proportional to the local reflection. Therefore, a single photodiode is sufficient to collect the signals from both channels simultaneously. A 180∘ phase shift in the tilt frequency of two calibrated micro-mirror areas leads to a superposition of the analyte and reference signal which enables an efficient reduction of the baseline offset and potential baseline offset drift. A performance test reveals that we are able to detect changes of the refractive index n down to Δn < 0.01 of saline solutions as regents. A further test validates the detection of heterogeneous binding interaction. This test compromises immobilized testosterone-bovine serum albumin on a three-dimensional layer of biopolymer as ligand and monoclonal anti-testosterone antibodies as analyte. Antibody/antigen binding induces a local growth of the biolayer and change in the refractive index, which is measured via the local change of the reflection. Reproducible measurements enable for the analysis of the binding kinetics by determining the affinity constant KA = 1.59 × 10- 7 M- 1. In summary, this work shows that the concept of differential Fourier spotting as novel setup for single-color reflectometry is suitable for reliable bioanalysis. Graphical Abstract.
Asunto(s)
Color , Óptica y Fotónica , Albúmina Sérica Bovina/análisis , Testosterona/análisis , Límite de Detección , Reproducibilidad de los ResultadosRESUMEN
Rate-responsive pacing based on the atrio-ventricular conduction time is a promising therapy for restoring physiological heart rate control in chronotropic incompetent patients. This paper compares four different algorithms. Three of them had been formulated as patents, but no real test or application has been reported up to now. The fourth was recently published by the authors of this paper. There the steps involved in the development process were stationary and dynamic system identification, control system design and a pilot study with patients. The data obtained were used to formulate a simulation model of the cardiac system by means of which the other algorithms were tested. Test criteria were stability, the attenuation of disturbances and the response time to changes of the exercise rate. None of the three patents worked when being strictly implemented as described. The problems encountered were instability, unusable parameterisations and some questionable adaptation mechanisms. In a redesign we tried to improve the patents, but only in one case would the results obtained justify real use. In the other cases the variability of the pacing frequency was intolerably high.