Sequential quantification of blood and diluent using red cell sedimentation-based separation and pressure-induced work in a microfluidic channel.

The erythrocyte sedimentation method has been widely used to detect inflammatory diseases. However, this conventional method still has several drawbacks, such as a large blood volume (∼1 mL) and difficulty in continuous monitoring. Most importantly, image-based methods cannot quantify RBC-rich blood (blood) and RBC-free blood (diluent) simultaneously. In this study, instead of visualizing interface movement in the blood syringe, a simple method is proposed to quantify blood and diluent in microfluidic channels sequentially. The hematocrit was set to 25% to enhance RBC sedimentation and form two layers (blood and diluent) in the blood syringe. An air cavity (∼300 μL) inside the blood syringe was secured to completely remove dead volumes (∼200 μL) in fluidic paths (syringe needle and tubing). Thus, a small blood volume ( V b = 50 μL) suctioned into the blood syringe is sufficient for supplying blood and diluent in the blood channel sequentially. The relative ratio of blood resident time (RBC-to-diluent separation) was quantified using λ b , which was obtained by quantifying the image intensity of blood flow. After the junction pressure ( P j ) and blood volume ( V ) were obtained by analyzing the interface in the coflowing channel, the averaged work ( W p [Pa mm 3 ]) was calculated and adopted to detect blood and diluent, respectively. The proposed method was then applied with various concentrations of dextran solution to detect aggregation-elevated blood. The W p of blood and diluent exhibited substantial differences with respect to dextran solutions ranging from C dex = 10 to C dex = 40 mg mL -1 . Moreover, λ b did not exhibit substantial differences in blood with C dex > 10 mg mL -1 . The variations in λ b were comparable to those of the previous method based on interface movement in the blood syringe. In conclusion, the W P could detect blood as well as diluents more effectively than λ b . Furthermore, the proposed method substantially reduced the blood volume from 1 mL to 50 μL.