Fig.1: Basic layout of an optical sensor system: The layer containing the analyte-sensitive dye (orange) is illuminated by an LED (green), and emits luminescent light of longer wavelength (red). The intensity as well as the decay time of the fluorescence are functions of the analyte concentration.Abstract-For most "simple" analytes (e.g. oxygen), the actual sensing element of optochemical sensors consists of a luminescent dye embedded in a polymeric matrix whose luminescence intensity and decay time correlates with the analyte concentration. The response characteristics of these sensors are limited by the time requirement for diffusion and equilibration of the analyte in the bulk of the matrix material. Traditionally, the sensor formulation is cast onto a substrate as a compact layer. Thin layers result in good response speed but poor signal intensity and signal-to-noise ratio, respectively. By means of electrospinning, many polymers can be processed to nanofibers, resulting in a highly-porous textile-like layer with high surfaceto-volume ratio and superb analyte accessibility. Doped with fluorescent dyes, such fiber layers are well suited for fast sensing applications where the response time is a critical issue. It was shown that by electrospinning of a typical oxygen sensor formulation (PtTFPP immobilized in polystyrene), that the response time t 90 can be accelerated from several seconds to less than 40ms at comparable general sensor performance. This work focuses on the long-term operational stability of such nanofiber based optical sensors. No pronounced tendency for degradation could be observed in long-term stress tests.
The nonradiative deactivation of the excited state of europium(III)-based phosphors via OH-vibrations in the presence of water allows the detection of moisture in nitrogen at concentration levels down to at least 25 ppm (0.09% RH).
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