OXYGEN DETECTION BY FLUORESCENCE QUENCHING OF TETRAPHENYLPORPHYRIN IMMOBILIZED IN THE ORIGINAL CLADDING OF AN OPTICAL-FIBER

A new fiber-optic sensor for oxygen has been developed. Tetraphenylpor phyrin (TPP), embedded into the original analyte-permeable cladding of a conventional low cost plastic-clad silica optical fiber, is excited by the evanescent-wave traveling in the fiber; the resulting fluoresc ence is captured back into the guided modes of the fiber and can be de tected at either end. Oxygen in the surrounding medium quenches the fl uorescence and is quantified by means of the Stern-Volmer expression. Excitation was achieved with an ultra-bright (13000 mcd) yellow 590 nm light-emitting diode (LED), with emission monitored at 650 nm. The ne w sensor offers excellent precision (relative standard deviation (RSD) of 0.1-0.2%) over the range of measured oxygen partial pressures (55- 760 torr), a response time of 1 s, a detection limit of 3.5 torr of ox ygen, and a quenching constant of 7.5x10(-4) torr(-1). Unlike earlier oxygen sensors, the new device is immune to changes in relative-humidi ty of measured gaseous samples. The short (10 ns) fluorescence lifetim e of TPP and the possibility to fabricate continuous chemically sensit ive fibers hundreds of meters long make the sensor attractive in appli cations that require spatially resolved oxygen mapping over large remo te areas. (C) 1998 Elsevier Science B.V. All rights reserved.