We have demonstrated a microfluidic device that can not only achieve three-dimensional flow focusing but also confine particles to the center stream along the channel. The device has a sample channel of smaller height and two sheath flow channels of greater height, merged into the downstream main channel where 3D focusing effects occur. We have demonstrated that both beads and cells in our device display significantly lower CVs in velocity and position distributions as well as reduced probability of coincidental events than they do in conventional 2D-confined microfluidic channels. The improved particle confinement in the microfluidic channel is highly desirable for microfluidic flow cytometers and in fluorescence-activated cell sorting (FACS). We have also reported a novel method to measure the velocity of each individual particle in the microfluidic channel. The method is compatible with the flow cytometer setup and requires no sophisticated visualization equipment. The principles and methods of device design and characterization can be applicable to many types of microfluidic systems.

We demonstrated a unique optofluidic lab-on-a-chip device that can measure optically encoded forward scattering signals. From the design of the spatial pattern, we can measure the position and velocity of each cell in the flow and generate a 2-D cell distribution plot over the cross section of the channel. Moreover, we have demonstrated that the cell distribution is highly sensitive to its size and stiffness. The latter is an important biomarker for cell classification and our method offers a simple and unequivocal method to classify cells by their size and stiffness. We have proved the concept using live and fixed HeLa cells. Due to the stiffness and size difference of neutrophils compared to other types of white blood cells, we have demonstrated detection of neutrophils from other blood cells. Finally, we have performed the test using 5 μL of human blood. In a greatly simplified blood preparation process, skipping the usual steps of anticoagulation, centrifuge, antibody labelling or staining, filtering, etc., we have demonstrated that our device and detection principle can count neutrophils in whole human blood. Our system is compact, inexpensive and simple to fabricate and operate, having a commodity laser diode and a Si PIN photoreceiver as the main pieces of hardware. Although the results are still preliminary, the studies indicate that this optofluidic device holds promise to be a point-of-care and home care device to measure neutrophil concentration, which is the key indicator of the immune functions for cancer patients undergoing chemotherapy.

Although flow cytometer, being one of the most popular research and clinical tools for biomedicine, can analyze cells based on cell size, internal structures such as granularity, and molecular markers, it provides little information about the physical properties of cells such as cell stiffness and physical interactions between cell membrane and fluid. In this paper, we propose a computational cell analysis technique using cells’ different equilibrium positions in a laminar flow. This method utilizes a spatial coding technique to acquire the spatial position of the cell in a microfluidic channel and then uses mathematical algorithms to calculate the ratio of cell mixtures. Most uniquely the invented computational cell analysis technique can unequivocally detect the subpopulation of each cell type without labeling even when the cell type shows a substantial overlap in the distribution plot with other cell types, a scenario limiting the use of conventional flow cytometers and machine learning techniques. To prove this concept, we have applied the computation method to distinguish live and fixed cancer cells without labeling, count neutrophil from human blood, and distinguish drug treated cells from untreated cells. Our work paves the way for using computation algorithms and fluidic dynamic properties for cell classification, a label-free method that can potentially classify over 200 types of human cells. Being a highly cost-effective cell analysis method complementary to flow cytometers, our method can offer orthogonal tests in companion with flow cytometers to provide crucial information for biomedical samples.