One possible drawback of electrospun sensors might consistsin the fact that increased accessibility for analytes also accountsfor an acceleration of degradation processes like photo bleachingof the fluorescent dye. In contrast to dye agglomeration phenom-ena, which seem unlikely in nanofibers due to the “entrapment”of the dye molecules in a nano-structure, the good accessibilityof oxygen may enhance the dye degradation caused by illumi-nation in the presence of oxygen, i.e. photo bleaching. In case ofnanofiber sensors, photo bleaching can be overcome by increasingthe thickness of the sensing layer. Due to the highly porous fiberstructure, a moderate increase in thickness does not lead to dete-riorated response times of the sensors; therefore and due to sideeffects like increased luminescence output caused by an enhancedlight scattering of the nanofibers, the intensity of the excitationlight can be decreased minimizing photo bleaching phenomena.Fig. 6 shows the results of long-term stress tests running for 6days with varying oxygen concentrations (Fig. 6a), leading to nochanges or drifts in the phase shift or intensity signal (phase shiftsee Fig. 6b, signal intensity loss