On-chip spectroscopic monitoring of erythrocyte oxygenation under hematocrit and oxygen gradients

Abstract

The interpretation of the variability and determinants of erythrocyte oxygenation is complicated by multiple interacting factors manifesting gaseous and fluidic microenvironments during microcirculation. In this paper, a multifunctional microdevice was developed for quantitatively extracting the dominant role of RBC concentration, local oxygen (O 2 ), and fluid dynamics in an ex vivo setting. Serial dilution of RBCs was achieved by repeated splitting and mixing of the source RBC suspension solutions in the bifurcating serpentine microchannels. O 2 perfusion of buried microchannels in a gas-permeable polydimethylsiloxane membrane allowed for exposing RBCs to a spatial linear O 2 gradient along with the blood flow direction. Taking the variability in the optically relevant properties of erythrocytes and their oxygenation status, an optical-fiber-based measurement system was integrated with the microfluidic device to capture the characteristic spectroscopic features of RBCs covering the visible to near-infrared range. The spectroscopic analysis provided a linear regression model of oxygen saturation with variables containing RBC concentrations, O 2 levels, and blood flow velocity, which agreed well with numerical simulation results. This systematic experimental approach could be applicable as an in vitro microcirculatory model system while adding a dimension to a wide range of blood processing and analysis. • A microfluidic device was developed for rendering serial RBC and O 2 gradients. • The vis-NIR spectra of RBCs were captured by an on-chip optical-fiber system. • The RBC oxygenation was studied with multiple variables and increased throughput. • Numerical simulation and vis-NIR spectra analysis showed a consistent StO 2 profile.