On-chip blood count

Abstract

Blood count is one of the most common medical laboratory tests performed today. It provides information on patient’s oxygen carrying capacity, immune system functionality, and the overall hemapoiesis process for disease diagnosis and drug side-effect monitoring. Traditionally blood count is performed either manually or by conventional automated blood analyzers. With the advance of microfabrication, on-chip blood count has become a target for miniaturization aiming at providing cost-effective, functional, capable point-of-care devices and systems that use less than 100 nL of blood sample and generate measurement results within minutes. The focus of this thesis is on investigation of erythrocyte/leukocyte counting and leukocyte differential, which are the two key components in blood count, in microdevices. Due to the large number ratio of erythrocytes to leukocytes and their property overlap, conventional automated blood analyzers accomplish blood count in several different channels by measuring different parameters. Similarly, in microdevices, it is desirable that erythrocytes and leukocytes can be separated before further analysis. Two types of hydrodynamic separation devices were investigated to continuously separate erythrocytes and leukocytes based on size. The principle of the device exploits the laminar flow in microdevices and design of streamlines which particles follow. Pillar-shaped devices with single geometrical design demonstrate a binary separation profile. With proper design, separation efficiency over 90% can be achieved. Channel-shaped devices, an improved design, can achieve similar separation efficiency with the added benefits of a smaller footprint, fewer requirements on flow control, and easier integration with downstream components. Erythrocyte and leukocyte count is accomplished with electrical impedance sensing, which is one of the most accurate ways to measure particle volume. The well-known problem of small double-layer capacitance inherent to micro impedance sensors is solved by two methods: platinum black electroplating on the electrode surface and inductor-induced resonance sensing. In the first method, platinum black is electroplated in situ on the electrode surfaces, which increases the effective surface area by two orders of magnitude and thus increases the double-layer capacitance significantly. The other innovative way, inductor-induced resonance sensing, nullifies the capacitive components in the system at the resonance frequency by connecting a parallel inductor to the system. In this way the sensitivity can be greatly improved and the optimal sensing frequency can be chosen from the inductance value. For both methods, polystyrene beads of different diameters were used for validation, while diluted blood samples and leukocyte-rich plasma were used to successfully demonstrate the feasibility. Two-part leukocyte differential is demonstrated in microflow cytometers with fluorescence sensing. Unlike methods used in conventional blood analyzers, undiluted blood samples are stained with nucleic acid stain acridine orange. Lymphocytes and granulocytes emit fluorescent light at different peak frequency after interaction with the dye due to the difference in cellular composition. Using the undiluted sample greatly minimizes sample preparation procedure, and reduces the overall measurement time, the reagent, and the waste volume. These benefits make it a practical method for implementation in microdevices. A throughput of one thousand leukocytes per second was demonstrated, which means the leukocyte differential could be accomplished in a couple of seconds.