Optochemical sensing of carbon dioxide

The research has been performed on photoluminescent materials suitable for sensing dissolved carbon dioxide (CO2) in biological fluids. It focuses on the formulation, processing and characterization of a multi-layer materials stack (MLMS), that fit the requirements of a sensor readout technique known as Dual Lifetime Referencing (DLR). In this system, a Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HPF) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl) trifluoro phosphate gel-membrane is doped with the fluorescent indicator hydroxypyrenetrisulfonic acid (HPTS) previously ion paired with Hexadecyltrimethylammonium bromide (CTABr) and stabilized by the internal buffer Hexadecyltrimethylammonium hydroxide (CTAO). The resulting layer was employed as analyte sensitive layer (Active Layer, AL). The reference luminophore, Ru(dpp), was embedded in poly acrylonitrile (PAN) forming reference layer (RL). Reference layer and active layer are separately bar-coated on a polycarbonate foil support. After their drying in an oven, a circular sensor spot of 0.5 cm of diameter is cut and characterized. Morphological characterization involves the study of the surface with WLI, XRD bulk analysis and fluorescent microscope analysis. Spectrophotometric properties are evaluated by the registration of emission and absorbance spectra. Sensing characterization is performed with an in-house developed optical setup, where a blue LED is used as excitation source and an optical spectrophotometer as detector. Only once reference layer demonstrates stability against O2 cross-sensitivity and the active layer demonstrates a stabilization of signal when exposed to different dCO2 concentrations, the two membranes are assembled together in one multi-layer material stack. The final MLMS demonstrates superior performance compared to AL and RL alone, in particular, a linear response to dCO2 was demonstrated.