Influence of polymeric matrix on optical oxygen sensor performance

The determination of oxygen concentration is important in many areas of industry, medicine and environment. Oxygen optical sensors are more and more attractive than conventional amperometric devices, because, in general, they have a faster response time, they do not consume oxygen and are less easily poisonable. Thin films containing oxygen-sensitive luminophores are widely used as in pressure sensitive paints (PSPs) because of their high sensitivity. Sensor operation is based on the quenching of luminescence in the presence of oxygen. Luminophores are commonly embedded in a polymeric matrix. Following the Stern-Volmer (SV) model, film sensibility ( ) is proportional to its permeability toward oxygen. The polymer may also influence the lifetime of the luminophore because it may modify the efficiency of non radiative processes due to luminophore-polymer interaction. Some matrices can also generate deviations from the linearity of the SV model, if they cannot be considered as a homogeneous media. If this happens a multisite model must be applied. The matrix may also enhance or diminish degradation of the embedded metal-complex due to light dependent phenomena and ageing processes, such as solvent residual evaporation and pore collapse. The aim of the present work is to show the results of some recent activities of our research group on different oxygen sensing membranes containing Platinum-tetraphenylporphyrin (PtTPP) embedded in various polymers. Each membrane was characterized for its optical properties and tested using the real background determination and various calibration models. A strong variation (100 times) of sensibility by varying the polymer nature was determined. Accuracy of each membrane was determined and rationalized using a numeric simulation1. A sensor containing 2 luminophores was created using suitable polymer and luminophores to obtain maximum accuracy and sensibility over the range 0-100% O2.