Ultra-fast opto-chemical sensors by using electrospun nanofibers as sensing layers

Optical sensors based on the principle of luminescence quenching of analyte-sensitive dyes gain increasing importance in numerous sensing applications, especially for oxygen detection. In general, the actual sensing element of these sensors consists of a specifically selected, analyte-sensitive luminescent dye immobilized in a compact polymer layer. The luminescence intensity and decay time change as a function of the analyte concentration and can be evaluated by appropriate equipment. The response dynamics of such opto-chemical sensors are limited by the rates of diffusion and equilibration of the analyte between the sample medium and the bulk of the sensor matrix material. The thicker the matrix layer, the slower the response. The appropriate sensor thickness therefore is a trade-off between response characteristics and signal intensity, i.e. general sensor performance. By means of electrospinning, many polymers can be processed to nanofibers, resulting in a non-woven fleece with a high surface-to-volume ratio and excellent analyte accessibility. Doped with fluorescent dyes, such fiber layers are well suited for fast sensing applications where the response time is a critical issue. In this work we replaced the compact oxygen-sensing layer of a standard oxygen sensor (oxygen-sensitive dye Pt-tetra(pentafluorophenyl) porphyrine (PtTFPP) immobilized in a polystyrene (PS) matrix) with a highly porous nanofiber layer electrospun from the same dye/matrix formulation. The response time t90 decreased by two orders of magnitude (from several seconds to less than 40 ms) while other sensor characteristics like sensitivity and signal intensity were maintained.