Leukocyte differential count is one of the most frequently ordered clinical tests in hospitals. This paper reports a point-of-care test for the leukocyte count by using a microflow cytometer and a fluorescent dye assay. The dye assay relied on fluorescent detection alone to count leukocytes in blood and to identify leukocyte subtypes. By combining the fluorescent assay with a sheathless microflow design, the proposed method achieved a minimal sample volume by eliminating excessive dilution and sheath flow. In this paper, a four-part leukocyte differential count including lymphocyte, monocyte, neutrophil and eosinophil was demonstrated, and the whole test consumed only a small amount of blood (5 μL) and reagents (68 μL in total). The merits of minimal sample volume, long reagent shelf life and portable instrument made this method optimal for point-of-care applications.

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The lack of simple but reliable microvalves is still a serious problem for many lab-on-a-chip applications. This work studied the use of blood coagulation, the transformation of liquid blood into solid coagulum, as a possible valving mechanism for microfluidic control and demonstrated a one-time open-to-close valve. This is done by creating a solidified blood coagulum, which clogs a normally-open fluidic channel as a closed valve. Local thermal coagulation is demonstrated using a focused laser for blood heating. This clogging valve can withstand a back pressure of 22 psig or higher and its simple structure is well-suited for disposable devices.