A novel planar optical sensor for simultaneous monitoring of oxygen, carbon dioxide, pH and temperature

The first quadruple luminescent sensor is presented which enables simultaneous detection of three chemical parameters and temperature. A multi-layer material is realized and combines two spectrally independent dually sensing systems. The first layer employs ethylcellulose containing the carbon dioxide sensing chemistry (fluorescent pH indicator 8-hydroxy-pyrene-1,3,6-trisulfonate (HPTS) and a lipophilic tetraalkylammonium base). The cross-linked polymeric beads stained with a phosphorescent iridium(III) complex are also dispersed in ethylcellulose and serve both for oxygen sensing and as a reference for HPTS. The second (pH/temperature) dually sensing system relies on the use of a pH-sensitive lipophilic seminaphthorhodafluor derivative and luminescent chromium(III)-activated yttrium aluminum borate particles (simultaneously acting as a temperature probe and as a reference for the pH indicator) which are embedded in polyurethane hydrogel layer. A silicone layer is used to spatially separate both dually sensing systems and to insure permeation selectivity for the CO2/O2 layer. The CO2/O2 and the pH/temperature layers are excitable with a blue and a red LED, respectively, and the emissions are isolated with help of optical filters. The measurements are performed at two modulation frequencies for each sensing system and the modified Dual Lifetime Referencing method is used to access the analytical information. The feasibility of the simultaneous four-parameter sensing is demonstrated. However, the practical applicability of the material may be compromised by its high complexity and by the performance of individual indicators.