Ratiometric fiber-optic oxygen sensors based on sol–gel matrix doped with metalloporphyrin and 7-amino-4-trifluoromethyl coumarin

This paper develops highly sensitive ratiometric fiber-optic oxygen sensors incorporating a sol–gel matrix doped with platinum or palladium tetrakis pentafluorophenyl porphine (PtTFPP or PdTFPP) metalloporphyrins as the oxygen-sensitive material and 7-amino-4-trifluoromethyl coumarin (AFC) as the reference dye. Using an LED with a central wavelength of 400 nm as an excitation source, it is shown that the emission wavelengths of the oxygen-sensitive dye and the reference dye have no spectral overlap and therefore permit the oxygen concentration to be measured using a ratiometric-based method. The sensitivities of the PtTFPP-doped and PdTFPP-doped oxygen sensors are evaluated in terms of the ratio IN2/IO2IN2/IO2, where IN2IN2 and IO2IO2 correspond to the detected luminescence intensities in pure nitrogen and pure oxygen, respectively. The experimental results reveal that the PtTFPP and PdTFPP sensors both yield linear Stern–Volmer plots and have sensitivities of around 33 and 74, respectively. In addition, the response time of the PtTFPP-doped sensor is found to be 2.8 s when switching from a fully deoxygenated environment (i.e. 100% nitrogen) to a fully oxygenated environment, and 5.8 s when switching in the reverse direction. The corresponding response times of the PdTFPP-doped sensor are 7.9 and 58.9 s, respectively. The ratiometric sensing approach presented in this study not only yields high sensitivity and reversibility, but also has the advantage of suppressing the effects of spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optic fiber.