Hydrodynamic focusing investigation in a micro-flow cytometer

Ultrahigh-Throughput, Real-Time Flow Cytometry for Rare Cell Quantification from Whole Blood

We present an ultrahigh-throughput, real-time fluorescence cytometer comprising a viscoelastic microfluidic system and a complementary metal-oxide-semiconductor (CMOS) linear image sensor-based detection system. The flow cytometer allows for real-time quantification of a variety of fluorescence species, including micrometer-sized particles and cells, at analytical throughputs in excess of 400,000 species per second. The platform integrates a custom C++ control program and graphical user interface (GUI) to allow for the processing of raw signals, adjustment of processing parameters, and display of fluorescence intensity histograms in real time. To demonstrate the efficacy of the platform for rare event detection and its utility as a basic clinical tool, we measure and quantify patient-derived circulating tumor cells (CTCs) in peripheral blood, realizing that detection has a sensitivity of 6 CTCs per million blood cells (0.000006%) with a volumetric throughput of over 3 mL/min.

Processes for the 3D Printing of Hydrodynamic Flow-Focusing Devices

Flow focusing is an important hydrodynamic technique for cytometric analysis, enabling the rapid study of cellular samples to identify a variety of biological processes. To date, the majority of flow-focusing devices are fabricated using conventional photolithography or flame processing of glass capillaries. This article presents a suite of low-cost, millifluidic, flow-focusing devices that were fabricated using a desktop sterolithgraphy (SLA) 3D printer. The suite of SLA printing strategies consists of a monolithic SLA method and a hybrid molding process. In the monolithic SLA approach, 1.3 mm square millifluidic channels were printed as a single piece. The printed device does not require any post processing, such as bonding or surface polishing for optical access. The hybrid molding approach consists of printing a mold using the SLA 3D printer. The mold is treated to an extended UV exposure and oven baked before using PDMS as the molding material for the channel. To demonstrate the viability of these channels, we performed a series of experiments using several flow-rate ratios to show the range of focusing widths that can be achieved in these devices. The experiments are validated using a numerical model developed in ANSYS.

Hydrodynamic flow cytometer performance enhancement by two-dimensional acoustic focusing

Conventional flow cytometers employ hydrodynamic focusing method to insure detection accuracy by forcing cells go through detected position. However, an increased flow velocity will significantly reduce detection precision due to a fact that cells will deviate center position and are easily silted in choke point. In an effort to overcome this limitation, a two-dimension ultrasonic particle focusing method are presented in this work to enhance the performance of flow cytometer. Two piezoelectric transducers are used to attach to a 250 μm × 250 μm rectangular fused silica flow channel to realize the modification. Finite element model simulation is performed for parametrical analysis and simplifying experiment design. 3 μm polystyrene fluorescent particles are adopted to test focusing effect. One dimension acoustic focusing is achieved at 2.95 MHz with single focusing node as well as 2, 3, 4 nodes focusing near 6, 9, 12 MHz respectively. The 2D focusing particle stream width in two dimensions is less than 10 μm. Results verified that this method is applicable for Jurkat cells. Sample flow maintains its stability without clogging up even at high sample concentration. Focusing still works at flow velocity over 100 μl/min. All these results certify this acoustic particles focusing method can enhance the performance of hydrodynamic flow cytometer by minor modification.

Disease diagnostics using hydrodynamic flow focusing in microfluidic devices: Beyond flow cytometry

The multi-disciplinary field of microfluidics has the potential to provide solutions to a diverse set of problems. It offers the advantages of high-throughput, continuous, rapid and expeditious analysis requiring minute quantities of sample. However, even as this field has yielded many mass-manufacturable and cost-efficient point-of-care devices, its direct and practical applications into the field of disease diagnostics still remain limited and largely overlooked by the industry. This review focuses on the phenomenon of hydrodynamic focusing and its potential to materialize solutions for appropriate diagnosis and prognosis. The study aims to look beyond its intended cytometric applications and focus on unambiguous disease detection, monitoring, drug delivery, studies conducted on DNA and highlight the instances in the scientific literature that have proposed such approach.

Stable microfluidic flow focusing using hydrostatics

We present a simple technique to generate stable hydrodynamically focused flows by driving the flow with hydrostatic pressure from liquid columns connected to the inlets of a microfluidic device. Importantly, we compare the focused flows generated by hydrostatic pressure and classical syringe pump driven flows and find that the stability of the hydrostatic pressure driven technique is significantly better than the stability achieved via syringe pumps, providing fluctuation-free focused flows that are suitable for sensitive microfluidic flow cytometry applications. We show that the degree of flow focusing with the hydrostatic method can be accurately controlled by the simple tuning of the liquid column heights. We anticipate that this approach to stable flow focusing will find many applications in microfluidic cytometry technologies.

Evaluating the liquid path stability of a flow cytometer

Precision in flow cytometry depends on many factors, the first of which is accurate and stable positioning of the hydrodynamically focused cells. However, no method exists to evaluate the stability of laminar flow and single-cell flow in the flow chamber of the flow cytometer directly because of the small size of the rectangular channel of the flow chamber. In this paper, a method of high-speed particle image velocimetry is proposed to solve this problem. The velocity stability of the particles in the flow chamber is used to evaluate the flow stability of the fluid path of the flow cytometer. The side scattering images of particles are obtained by a high-speed camera. Upon exposure, cells were imaged at random positions in the flow cell, resulting in four different types of the images: blank, inadequate, normal, or overlapped. Normal images were identified utilizing a grey cluster analysis algorithm based on trapezoid whitenization weight functions. A mid-point method is applied to determine the length of the particle track at a fixed exposure time. The variation of the trajectory lengths of the normal images are used to evaluate the stability of the liquid path. Experiments are carried out to verify the feasibility of our method in which different diameter microspheres at different flow rates. The results indicate that the standard deviation and relative standard deviation of the trajectory lengths can be used as the evaluation indices of the liquid path stability of the flow cytometer. © 2016 International Society for Advancement of Cytometry.

High-throughput flow alignment of barcoded hydrogel microparticles

Suspension (particle-based) arrays offer several advantages over conventional planar arrays in the detection and quantification of biomolecules, including the use of smaller sample volumes, more favorable probe-target binding kinetics, and rapid probe-set modification. We present a microfluidic system for the rapid alignment of multifunctional hydrogel microparticles designed to bear one or several biomolecule probe regions, as well as a graphical code to identify the embedded probes. Using high-speed imaging, we have developed and optimized a flow-through system that (1) allows for a high particle throughput, (2) ensures proper particle alignment for decoding and target quantification, and (3) can be reliably operated continuously without clogging. A tapered channel flanked by side focusing streams is used to orient the flexible, tablet-shaped particles into a well-ordered flow in the center of the channel. The effects of channel geometry, particle geometry, particle composition, particle loading density, and barcode design are explored to determine the best combination for eventual use in biological assays. Particles in the optimized system move at velocities of approximately 50 cm s(-1) and with throughputs of approximately 40 particles s(-1). Simple physical models and CFD simulations have been used to investigate flow behavior in the device.

Multiplexed detection of bacteria and toxins using a microflow cytometer

A microfabricated flow cytometer was used to demonstrate multiplexed detection of bacteria and toxins using fluorescent coded microspheres. Antibody-coated microspheres bound biothreat targets in a sandwich immunoassay format. The microfluidic cytometer focused the microspheres in three dimensions within the laser interrogation region using passive groove structures to surround the sample stream with sheath fluid. Optical analysis at four different wavelengths identified the coded microspheres and quantified target bound by the presence of phycoerythrin tracer. The multiplexed assays in the microflow cytometer had performance approaching that of a commercial benchtop flow cytometer. The respective limits of detection for bacteria (Escherichia coli, Listeria, and Salmonella) were found to be 10(3), 10(5), and 10(4) cfu/mL for the microflow cytometer and 10(3), 10(6), and 10(5) cfu/mL for the commercial system. Limits of detection for the toxins (cholera toxin, staphylococcal enterotoxin B, and ricin) were 1.6, 0.064, and 1.6 ng/mL for the microflow cytometer and 1.6, 0.064, and 8.0 ng/mL for the commercial system.

Parasitic trap cancellation using multiple frequency dielectrophoresis, demonstrated by loading cells into cages

This paper presents a method of using multiple frequencies to counteract electric field distortions that interfere with the dielectrophoretic (DEP) manipulation of particles or cells. To demonstrate the technique, simulations were performed for a scenario in which cells were to be loaded into a cage whose walls created parasitic trapping sites that prevented cells from entering it. By employing negative DEP on one electrode in conjunction with positive DEP on another, these traps could be almost completely cancelled. The model predictions were validated experimentally: multiple frequency DEP was used to load many cells into a cage in a matter of seconds in fluid flows of up to 300 microm s(-1), which could not be done with single frequency DEP. Actively cancelling field distortions permits the presence of features that would otherwise be prohibited near regions of dielectrophoretic manipulation, significantly expanding the environments in which dielectrophoresis can be used.