Characterization of 3D oxygen concentrations in microfluidic systems combining astigmatic particle tracking with phosphorescence decay measurements

Abstract

In this work, we combine astigmatic particle tracking with phosphorescence decay measurements to determine 3D-resolved oxygen concentration in microfluidic systems. In our experiments we achieve uncertainties in the out-of-plane position of less than 1 µm and uncertainties in oxygen concentration of less than 2 ppm. The calibrated measurement range covers oxygen concentrations of 0.6 ppm to 27.6 ppm. A method is presented to correct for measurement errors caused by photobleaching. For this, the excitation energy, the cumulative exposure time and the spatially varying intensity profile of the laser are taken into account in the correction. With this method, low measurement errors of less than 2ppm at ambient oxygen levels can be achieved even after thousands of excitation cycles. Hence, 3D oxygen concentrations are measured in an agarose hydrogel filled microfluidic chamber across which different pressure and oxygen gradients can be set independently. The results show that oxygen diffusion is superposed by an interstitial flow, which significantly alters the resulting oxygen concentration.