Optochemical sensors based on polymer nanofibers with ultra-fast response characteristics

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 surface-to-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 t₉₀ 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.