Rationalization of the behaviour of a bi-label oxygen optical sensor

The determination of oxygen concentration is important in many areas of industry, medicine and the 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. Sensor operation is based on the quenching of luminescence in the presence of oxygen. We rationalized the behaviour of an oxygen optical sensor made of two luminophores simultaneously embedded in polymeric matrices[1]. Theoretical findings were confirmed by experiments. Platinum(II) 5,10,15,20-tetraphenyl-21H,23H-porphyrin (PtTPP), Palladium(II) 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin (PdFTPP), Ruthenium (II) (4,7-diphenyl-l,l0-phenanthroline)3 (octylsulfate)2 (Ru(dpp)OS) were used as luminophores and embedded either in polyvinylchloride or in polysulfone matrices. Their different life-times allowed preparing sensing membranes having optimized precision in the required concentration interval by proportioning the luminophores relative amounts. We demonstrated that, in the experimental conditions adopted, the two luminophores behave as if they were independent, giving to the sensing layer enlarged working range with respect to the most sensitive membrane and improved precision with respect to the less sensitive membrane. A working curve may indicate the most suitable membrane composition. The choice of a bi-label sensor may be justified when it is necessary to detect oxygen in a chosen concentration interval with the best precision possible.