O₂ Optodes for Analyzing Micro Blood Samples Using Thin Sensor Layers with Small O₂ Capacities and Special Reflection Properties for Optical Decoupling of Sensor and Sample

Abstract

By incorporating an O₂-sensitive fluorescence indicator into a poly­meric membrane the membrane can be used to measure the pO₂ in a sample (Lübbers and Opitz, 1983) or on organ surfaces (Opitz and Lübbers, this volume). However, with measurements in different samples, e.g. blood and gas, reflection changes occur at the optical phase transition sensor/ medium due to different optical densities of the various media to be measured. These reflection changes originating from both excitation- and fluorescence radiation (impinging either directed or undirected on the phase transition, respectively), cannot be eliminated by a simple refe­rence measurement with the aid of a fluoresence standard, because of the wavelength dependence of the refractive index n (optical dispersion). As an example, Fig. 1 shows two corrected excitation spectra (λ_em = 420 nm) of an O₂-sensitive perylene derivative (Kroneis and Marsoner, 1983) monitored by means of an optode-device for micro blood samples (sample volume ca. 70/ul) in gas and Ringer’s solution, both equilibrated with 20 % oxygen. Since both spectra differ significantly, calibration curves in various media are not identical.