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.
The inner structure, especially the nuclear structure, of cells carries valuable information about disease and health conditions of a person. Here we demonstrate a label-free technique to enable direct observations and measurements of the size, shape and morphology of the cell nucleus. With a microfabricated lens and a commercial CMOS imager, we form a scanning light-sheet microscope to produce a dark-field optical scattering image of the cell nucleus that overlays with the bright-field image produced in a separate regime of the same CMOS sensor. We have used the device to detect nuclear features that characterize the life cycle of cells and have used the nucleus volume as a new parameter for cell classification. The device can be developed into a portable, low-cost, point-of-care device leveraging the capabilities of the CMOS imagers to be pervasive in mobile electronics.
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.
We demonstrated an optical coding method to measure the position of each particle in a microfluidic channel. The technique utilizes a specially designed pattern as a spatial mask to encode the forward scattering signal of each particle. From the waveform of the forward scattering signal, one can obtain the information about the particle position and velocity. The technique enables us to experimentally investigate the complex relations between particle positions within the microfluidic channel and flow conditions and particle sizes. The method also produces insight for important phenomenon in microfluidic and lab-on-a-chip devices such as inertial focusing, Dean flow, flow confinement, etc.
An "optical space-time coding method" was applied to microfluidic devices to detect the forward and large angle light scattering signals for unlabelled bead and cell detection. Because of the enhanced sensitivity by this method, silicon pin photoreceivers can be used to detect both forward scattering (FS) and large angle (45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60) ) scattering (LAS) signals, the latter of which has been traditionally detected by a photomultiplier tube. This method yields significant improvements in coefficients of variation (CV), producing CVs of 3.95% to 10.05% for FS and 7.97% to 26.12% for LAS with 15 lm, 10 lm, and 5 lm beads. These are among the best values ever demonstrated with microfluidic devices. The optical spacetime coding method also enables us to measure the speed and position of each particle, producing valuable information for the design and assessment of microfluidic lab-on-a-chip devices such as flow cytometers and complete blood count devices. Particle counting and differentiation based on optical detection in microfluidic devices has attracted significant attention because the technology promises cheaper, portable, and easy-tooperate devices for research, clinical, environmental, and industrial applications.1-4 In a conventional design, the suspended particles in a microfluidic channel are directed in a stream to an interrogation area where optical scattering, fluorescence, and Raman signals as well as electrical signals such as impedance are detected to reveal the intrinsic properties of the sample. According to the detected signals, particle separation methods based on hydrodynamic, dielectrophoretic, optical, acoustic, or magnetic mechanisms may be applied to direct the particles to the designated downstream channels, a function called cell sorting to isolate subpopulations of cells from the biological sample. [5][6][7] For both sample analysis and sorting, detection of the intrinsic properties of each particle is the most critical step and is particularly important for single-cell analysis in contrast with detection of the average properties of an ensemble. Here, forward scattering (FS) and large angle scattering (LAS) or side-scattering (SS) signals are the most commonly used signals for bead and cell analysis since these signals reveal the size, shape, and granularity of each individual particle without the need for labeling which adds complexity, cost, and potentially bias to the subjects. However, side scattering signals are orders of magnitude weaker and usually detected by photomultiplier tubes (PMTs) which require high voltage (> 1000 V) operation and are expensive and fragile, not suitable for point-of-care clinics. 8,9 Furthermore, most microfluidic devices produce weaker and more noisy side scattering signals than commercial systems, and the large coefficients of variation (CV) values of microfluidic devices have severely limited the applicability of the side scattering signals in devices such as flow cytometers and complete blood count (CBC...
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