Oxygen detection by fluorescence quenching of tetraphenylporphyrin immobilized in the original cladding of an optical fiber

Abstract

A new fiber-optic sensor for oxygen has been developed. Tetraphenylporphyrin (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 fluorescence is captured back into the guided modes of the fiber and can be detected at either end. Oxygen in the surrounding medium quenches the fluorescence and is quantified by means of the Stern–Volmer expression. Excitation was achieved with an ultra-bright (13 000 mcd) yellow 590 nm light-emitting diode (LED), with emission monitored at 650 nm. The new 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 oxygen, and a quenching constant of 7.5×10 −4 torr −1. Unlike earlier oxygen sensors, the new device is immune to changes in relative-humidity of measured gaseous samples. The short (10 ns) fluorescence lifetime of TPP and the possibility to fabricate continuous chemically sensitive fibers hundreds of meters long make the sensor attractive in applications that require spatially resolved oxygen mapping over large remote areas.