On-chip counting the number and the percentage of CD4+ T lymphocytes

A Review of Single-Cell Adhesion Force Kinetics and Applications

Cells exert, sense, and respond to the different physical forces through diverse mechanisms and translating them into biochemical signals. The adhesion of cells is crucial in various developmental functions, such as to maintain tissue morphogenesis and homeostasis and activate critical signaling pathways regulating survival, migration, gene expression, and differentiation. More importantly, any mutations of adhesion receptors can lead to developmental disorders and diseases. Thus, it is essential to understand the regulation of cell adhesion during development and its contribution to various conditions with the help of quantitative methods. The techniques involved in offering different functionalities such as surface imaging to detect forces present at the cell-matrix and deliver quantitative parameters will help characterize the changes for various diseases. Here, we have briefly reviewed single-cell mechanical properties for mechanotransduction studies using standard and recently developed techniques. This is used to functionalize from the measurement of cellular deformability to the quantification of the interaction forces generated by a cell and exerted on its surroundings at single-cell with attachment and detachment events. The adhesive force measurement for single-cell microorganisms and single-molecules is emphasized as well. This focused review should be useful in laying out experiments which would bring the method to a broader range of research in the future.

Cytomorphology-based microchip with contour extraction processing for bioparticle analysis

In this paper, we demonstrated an integrated digital image processing framework that is training-free for high throughput beads or biological cells detection and enumeration by the bead aggregation splitting algorithm. By making contour extraction processing, the aggregated beads can be clearly split for precise counting. It can be potentially embedded on-chip in a miniaturized medical equipment to automatically adjust illumination condition and de-noise. This study demonstrates that the existing hematological analysis can be updated from manual classification and counting by high-speed and precise machine-based programs.

Microfluidic device embedding electrodes for dielectrophoretic manipulation of cells-A review

Microfluidic device embedding electrodes realizes cell manipulation with the help of dielectrophoresis. Cell manipulation is an important technology for cell sorting and cell population purification. Till now, the theory of dielectrophoresis has been greatly developed. Microfluidic devices with various arrangements of electrodes have been reported from the beginning of the single non-uniform electric field to the later multiple physical fields. This paper reviews the research status of microfluidic device embedding electrodes for cell manipulation based on dielectrophoresis. Firstly, the working principle of dielectrophoresis is explained. Next, cell manipulation approaches based on dielectrophoresis are introduced. Then, different types of electrode arrangements in the microfluidic device for cell manipulation are discussed, including planar, multilayered and microarray dot electrodes. Finally, the future development trend of the dielectrophoresis with the help of microfluidic devices is prospected. With the rapid development of microfluidic technology, in the near future, high precision, high throughput, high efficiency, multifunctional, portable, economical and practical microfluidic dielectrophoresis will be widely used in the fields of biology, medicine, agriculture and so on.

Lab-on-Chip for Exosomes and Microvesicles Detection and Characterization

Interest in extracellular vesicles and in particular microvesicles and exosomes, which are constitutively produced by cells, is on the rise for their huge potential as biomarkers in a high number of disorders and pathologies as they are considered as carriers of information among cells, as well as being responsible for the spreading of diseases. Current methods of analysis of microvesicles and exosomes do not fulfill the requirements for their in-depth investigation and the complete exploitation of their diagnostic and prognostic value. Lab-on-chip methods have the potential and capabilities to bridge this gap and the technology is mature enough to provide all the necessary steps for a completely automated analysis of extracellular vesicles in body fluids. In this paper we provide an overview of the biological role of extracellular vesicles, standard biochemical methods of analysis and their limits, and a survey of lab-on-chip methods that are able to meet the needs of a deeper exploitation of these biological entities to drive their use in common clinical practice.

Biophysical measurement of red blood cells by laboratory on print circuit board chip

Microfluidic impedance pulse sensor has emerged as an easily handled and low-cost platform in the electrical analysis of biological cells. In the conventional method, impedance sensor demanded expensive patterning metal electrodes on the substrate, which are directly in touch with electrolytes in order to measure the microfluidic channel impedance change. In this article, a cost-effective microfluidic impedance sensor built upon a dielectric film coated printed circuit board is introduced. Impedance electrodes are protected by a dielectric film layer from electrochemical erosion between electrodes and electrolyte. Human red blood cells from adult and neonatal were utilized to demonstrate the feasibility of the proposed device in the electroanalysis of biological cells.

A Single-Bead-Based, Fully Integrated Microfluidic System for High-Throughput CD4+T Lymphocyte Enumeration

A single-bead-based, fully integrated microfluidic system has been developed for high-throughput CD4+T lymphocyte enumeration at point-of-care testing. Instead of directly counting CD4+T lymphocytes, CD4+T lymphocyte enumeration is achieved by quantitatively detecting CD4 antigen from the lysed blood sample with a functionalized polycarbonate single bead based on chemiluminescence. To implement the sandwiched chemiluminescence immunoassay with reduced nonspecific binding, a streamlined microfluidic chip with multiple reaction chambers is developed to allow each reaction step to be completed in an independent chamber where reagent is pre-stored. With simple magnetic control, the single bead with an embedded ferrous core can be consecutively transported between each of two adjacent chambers for different reactions. Meanwhile, enhanced mixing can be achieved by moving the single bead back and forth inside one chamber with magnetic actuation. High-throughput detection can be performed when a linear actuation stage is adopted to introduce synchronous magnetic control to multiple single beads in parallel microfluidic chips. A sensitive charge-coupled device (CCD) camera is adopted for high-throughput chemiluminescence detection from multiple single beads. Experimental results show that with the fully integrated microfluidic system, easy-to-operate, accurate, low-cost, immediate, and high-throughput CD4+T lymphocyte enumeration can be successfully achieved at resource-poor settings.

Multi-parameter analysis using photovoltaic cell-based optofluidic cytometer

A multi-parameter optofluidic cytometer based on two low-cost commercial photovoltaic cells and an avalanche photodetector is proposed. The optofluidic cytometer is fabricated on a polydimethylsiloxane (PDMS) substrate and is capable of detecting side scattered (SSC), extinction (EXT) and fluorescence (FL) signals simultaneously using a free-space light transmission technique without the need for on-chip optical waveguides. The feasibility of the proposed device is demonstrated by detecting fluorescent-labeled polystyrene beads with sizes of 3 μm, 5 μm and 10 μm, respectively, and label-free beads with a size of 7.26 μm. The detection experiments are performed using both single-bead population samples and mixed-bead population samples. The detection results obtained using the SSC/EXT, EXT/FL and SSC/FL signals are compared with those obtained using a commercial flow cytometer. It is shown that the optofluidic cytometer achieves a high detection accuracy for both single-bead population samples and mixed-bead population samples. Consequently, the proposed device provides a versatile, straightforward and low-cost solution for a wide variety of point-of-care (PoC) cytometry applications.

Integrating Cell Phone Imaging with Magnetic Levitation (i-LEV) for Label-Free Blood Analysis at the Point-of-Living

There is an emerging need for portable, robust, inexpensive, and easy-to-use disease diagnosis and prognosis monitoring platforms to share health information at the point-of-living, including clinical and home settings. Recent advances in digital health technologies have improved early diagnosis, drug treatment, and personalized medicine. Smartphones with high-resolution cameras and high data processing power enable intriguing biomedical applications when integrated with diagnostic devices. Further, these devices have immense potential to contribute to public health in resource-limited settings where there is a particular need for portable, rapid, label-free, easy-to-use, and affordable biomedical devices to diagnose and continuously monitor patients for precision medicine, especially those suffering from rare diseases, such as sickle cell anemia, thalassemia, and chronic fatigue syndrome. Here, a magnetic levitation-based diagnosis system is presented in which different cell types (i.e., white and red blood cells) are levitated in a magnetic gradient and separated due to their unique densities. Moreover, an easy-to-use, smartphone incorporated levitation system for cell analysis is introduced. Using our portable imaging magnetic levitation (i-LEV) system, it is shown that white and red blood cells can be identified and cell numbers can be quantified without using any labels. In addition, cells levitated in i-LEV can be distinguished at single-cell resolution, potentially enabling diagnosis and monitoring, as well as clinical and research applications.

Human T cells monitored by impedance spectrometry using field-effect transistor arrays: a novel tool for single-cell adhesion and migration studies

Cytotoxic T lymphocytes (CTLs) play an important role in the immune system by recognizing and eliminating pathogen-infected and tumorigenic cells. In order to achieve their function, T cells have to migrate throughout the whole body and identify the respective targets. In conventional immunology studies, interactions between CTLs and targets are usually investigated using tedious and time-consuming immunofluorescence imaging. However, there is currently no straightforward measurement tool available to examine the interaction strengths. In the present study, adhesion strengths and migration of single human CD8(+) T cells on pre-coated field-effect transistor (FET) devices (i.e. fibronectin, anti-CD3 antibody, and anti-LFA-1 antibody) were measured using impedance spectroscopy. Adhesion strengths to different protein and antibody coatings were compared. By fitting the data to an electronically equivalent circuit model, cell-related parameters (cell membrane capacitance referring to cell morphology and seal resistance referring to adhesion strength) were obtained. This electronically-assessed adhesion strength provides a novel, fast, and important index describing the interaction efficiency. Furthermore, the size of our detection transistor gates as well as their sensitivity reaches down to single cell resolution. Real-time motions of individually migrating T cells can be traced using our FET devices. The in-house fabricated FETs used in the present study are providing a novel and very efficient insight to individual cell interactions.

Design of a fluidic circuit-based microcytometer for circulating tumor cell detection and enumeration

Portable devices have been introduced to provide companion diagnostics in many applications such as personalized healthcare monitoring since several decades ago. Recently the polydimethylsiloxane (PDMS)-based microfluidic chip enables a cost effective platform for point of care diagnostics. In this paper, we present a systematic theoretical and experimental study of a novel fluidic circuit-based microcytometer. The working principle of this device is based on the characterization of the bandwidth and amplitude of the bias-voltage pulses induced by the microparticle's physical blockage of the sensing aperture. In the simulation, the amplitude and bandwidth of the bias voltage change is simply related to the microparticle translocation time and resistance change in the sensing aperture. In the modeling part, we simulate the two parameters (peak and translocation time) by considering 7 μm and 16 μm, which is used to approximately characterize the Red Blood Cells (RBCs) and Circulating Tumor Cells (CTCs). In the experimental setup, microparticles of different sizes are used to demonstrate the chip performance. Furthermore, RBCs and CTCs are detected and enumerated by the proposed chip. The microcytometry chip is presented and is expected toward the point of care clinical diagnostics.

Micro- and nanotechnology for HIV/AIDS diagnostics in resource-limited settings

Thirty-four million people are living with HIV worldwide, a disproportionate number of whom live in resource-limited settings. Proper clinical management of AIDS, the disease caused by HIV, requires regular monitoring of both the status of the host's immune system and levels of the virus in their blood. Therefore, more accessible technologies capable of performing a CD4+ T cell count and HIV viral load measurement in settings where HIV is most prevalent are desperately needed to enable better treatment strategies and ultimately quell the spread of the virus within populations. This review discusses micro- and nanotechnology solutions to performing these key clinical measurements in resource-limited settings.

CD4 counting technologies for HIV therapy monitoring in resource-poor settings--state-of-the-art and emerging microtechnologies

Modern advancements in pharmaceuticals have provided individuals who have been infected with the human immunodeficiency virus (HIV) with the possibility of significantly extending their survival rates. When administered sufficiently soon after infection, antiretroviral therapy (ART) allows medical practitioners to control onset of the symptoms of the associated acquired immune deficiency syndrome (AIDS). Active monitoring of the immune system in both HIV patients and individuals who are regarded as "at-risk" is critical in the decision making process for when to start a patient on ART. A reliable and common method for such monitoring is to observe any decline in the number of CD4 expressing T-helper cells in the blood of a patient. However, the technology, expertise, infrastructure and costs to carry out such a diagnostic cannot be handled by medical services in resource-poor regions where HIV is endemic. Addressing this shortfall, commercialized point-of-care (POC) CD4 cell count systems are now available in such regions. A number of newer devices will also soon be on the market, some the result of recent maturing of charity-funded initiatives. Many of the current and imminent devices are enabled by microfluidic solutions, and this review will critically survey and analyze these POC technologies for CD4 counting, both on-market and near-to-market deployment. Additionally, promising technologies under development that may usher in a new generation of devices will be presented.

Albumin-coated monodisperse magnetic poly(glycidyl methacrylate) microspheres with immobilized antibodies: application to the capture of epithelial cancer cells

Monodisperse (4 μm) macroporous crosslinked poly(glycidyl methacrylate) (PGMA) microspheres for use in microfluidic immunomagnetic cell sorting, with a specific application to the capture of circulating tumor cells (CTCs), were prepared by multistep swelling polymerization in the presence of cyclohexyl acetate porogen and hydrolyzed and ammonolyzed. Iron oxide was then precipitated in the microspheres to render them magnetic. Repeated precipitation made possible to raise the iron oxide content to more than 30 wt %. To minimize nonspecific adsorption of the microspheres in a microchannel and of cells on the microspheres, they were coated with albumin crosslinked with glutaraldehyde. Antibodies of epithelial cell adhesion molecule (anti-EpCAM) were then immobilized on the albumin-coated magnetic microspheres using the carbodiimide method. Capture of breast cancer MCF7 cells as a model of CTCs by the microspheres with immobilized anti-EpCAM IgG was performed in a batch experiment. Finally, MCF7 cells were captured by the anti-EpCAM-immobilized albumin-coated magnetic microspheres in an Ephesia chip. A very good rejection of lymphocytes was achieved. Thus, albumin-coated monodisperse magnetic PGMA microspheres with immobilized anti-EpCAM seem to be promising for capture of CTCs in a microfluidic device.

Solution-gated graphene field effect transistors integrated in microfluidic systems and used for flow velocity detection

Solution-gated graphene field effect transistors (SGGT) were integrated in microfluidic systems. The transfer characteristics of a SGGT with an Ag/AgCl gate electrode shifted horizontally with the change of the ionic concentration of KCl solution in the microchannel and the relationship can be fitted with the Nernst equation, which was attributed to the change of the potential drop at the Ag/AgCl electrode. Therefore the gate electrode is one important factor for the ion sensitive property of the SGGT. Then SGGTs were used as flow velocity sensors, which were based on measuring the streaming potentials in microfluidic channels. A linear relationship between the shift of the transfer curve of the SGGT and the flow velocity was obtained, indicating that the SGGT is a promising transducer for measuring flow velocity in a microchip. Since the streaming potential is influenced by the three physical quantities, including the flow velocity, the ionic strength of the fluid and the zeta potential of the substrate, the device can be used for sensing any one of the three quantities when the other two were known. It is noteworthy that SGGTs have been used for various types of chemical and biological sensors. Array of the devices integrated in multichannel microchips are expected to find many important applications in the lab-on-a-chip systems in the future.

Emerging technologies for point-of-care CD4 T-lymphocyte counting

A CD4 T-lymphocyte count determines eligibility for antiretroviral therapy (ART) in patients recently diagnosed with HIV and also monitors the efficacy of ART treatment thereafter. ART slows the progression of HIV to AIDS. In the developing world, CD4 tests are often performed in centralized laboratories, typically in urban areas. The expansion of ART programs into rural areas has created a need for rapid CD4 counting because logistical barriers can delay the timely dissemination of test results and affect patient care through delay in intervention or loss of follow-up care. CD4 measurement at the point-of-care (POC) in rural areas could help the facilitation of ART and monitoring of treatment. This review highlights recent technology developments with applications towards determining CD4 counts at the POC.

Enumeration of CD4+ T-cells using a portable microchip count platform in Tanzanian HIV-infected patients

BACKGROUND

CD4(+) T-lymphocyte count (CD4 count) is a standard method used to monitor HIV-infected patients during anti-retroviral therapy (ART). The World Health Organization (WHO) has pointed out or recommended that a handheld, point-of-care, reliable, and affordable CD4 count platform is urgently needed in resource-scarce settings.

METHODS

HIV-infected patient blood samples were tested at the point-of-care using a portable and label-free microchip CD4 count platform that we have developed. A total of 130 HIV-infected patient samples were collected that included 16 de-identified left over blood samples from Brigham and Women's Hospital (BWH), and 114 left over samples from Muhimbili University of Health and Allied Sciences (MUHAS) enrolled in the HIV and AIDS care and treatment centers in the City of Dar es Salaam, Tanzania. The two data groups from BWH and MUHAS were analyzed and compared to the commonly accepted CD4 count reference method (FACSCalibur system).

RESULTS

The portable, battery operated and microscope-free microchip platform developed in our laboratory (BWH) showed significant correlation in CD4 counts compared with FACSCalibur system both at BWH (r = 0.94, p<0.01) and MUHAS (r = 0.49, p<0.01), which was supported by the Bland-Altman methods comparison analysis. The device rapidly produced CD4 count within 10 minutes using an in-house developed automated cell counting program.

CONCLUSIONS

We obtained CD4 counts of HIV-infected patients using a portable platform which is an inexpensive (<$1 material cost) and disposable microchip that uses whole blood sample (<10 µl) without any pre-processing. The system operates without the need for antibody-based fluorescent labeling and expensive fluorescent illumination and microscope setup. This portable CD4 count platform displays agreement with the FACSCalibur results and has the potential to expand access to HIV and AIDS monitoring using fingerprick volume of whole blood and helping people who suffer from HIV and AIDS in resource-limited settings.

Label-free resistive-pulse cytometry

Numerous methods have recently been developed to characterize cells for size, shape, and specific cell-surface markers. Most of these methods rely upon exogenous labeling of the cells and are better suited for large cell populations (>10,000). Here, we review a label-free method of characterizing and screening cells based on the Coulter-counter technique of particle sizing: an individual cell transiting a microchannel (or "pore") causes a downward pulse in the measured DC current across that "pore". Pulse magnitude corresponds to the cell size, pulse width to the transit time needed for the cell to pass through the pore, and pulse shape to how the cell traverses across the pore (i.e., rolling or tumbling). When the pore is functionalized with an antibody that is specific to a surface-epitope of interest, label-free screening of a specific marker is possible, as transient binding between the two results in longer time duration than when the pore is unfunctionalized or functionalized with a nonspecific antibody. While this method cannot currently compete with traditional technology in terms of throughput, there are a number of applications for which this technology is better suited than current commercial cytometry systems. Applications include the rapid and nondestructive analysis of small cell populations (<100), which is not possible with current technology, and a platform for providing true point-of-care clinical diagnostics, due to the simplicity of the device, low manufacturing costs, and ease of use.

A Microfluidic Passive Pumping Coulter Counter

A microfluidic device using on-chip passive pumping was characterized for use as a particle counter. Flow occurred due to a Young-Laplace pressure gradient between two 1.2 mm diameter inlets and a 4 mm diameter reservoir when 0.5μ L fluid droplets were applied to the inlets using a micropipette. Polystyrene particles (10μm diameter) were enumerated using the resistive pulse technique. Particle counts using passive pumping were within 13% of counts from a device using syringe pumping. All pumping methods produced particle counts that were within 16% of those obtained with a hemocytometer. The effect of intermediate wash steps on particle counts within the passive pumping device was determined. Zero, one, or two wash droplets were loaded after the first of two sample droplets. No statistical difference was detected in the mean particle counts among the loading patterns (p > 0.05). Hydrodynamic focusing using passive pumping was also demonstrated.

Tunable two-dimensional liquid gradient refractive index (L-GRIN) lens for variable light focusing

We report a two-dimensional (2D) tunable liquid gradient refractive index (L-GRIN) lens for variable focusing of light in the out-of-plane direction. This lens focuses a light beam through a liquid medium with a 2D hyperbolic secant (HS) refractive index gradient. The refractive index gradient is established in a microfluidic chamber through the diffusion between two fluids with different refractive indices, i.e. CaCl(2) solution and deionized (DI) water. The 2D HS refractive index profile and subsequently the focal length of the L-GRIN lens can be tuned by changing the ratio of the flow rates of the CaCl(2) solution and DI water. The focusing effect is experimentally characterized through side-view and top-view image analysis, and the experimental data match well with the results from ray-tracing optical simulations. Advantages of the 2D L-GRIN lens include simple device fabrication procedure, low fluid consumption rate, convenient lens-tuning mechanism, and compatibility with existing microfluidic devices. We expect that with further optimizations, this 2D L-GRIN lens can be used in many optics-based lab-on-a-chip applications.

An integrated microfluidic system for isolation, counting, and sorting of hematopoietic stem cells

This study reports an integrated microfluidic system capable of isolation, counting, and sorting of hematopoietic stem cells (HSCs) from cord blood in an automatic format by utilizing a magnetic-bead-based immunoassay. Three functional modules, including cell isolation, cell counting, and cell sorting modules are integrated on a single chip by using microfluidic technology. The cell isolation module is comprised of a four-membrane-type micromixer for binding of target stem cells and magnetic beads, two pneumatic micropumps for sample transport, and an S-shaped channel for isolation of HSCs using a permanent magnet underneath. The counting and sorting of HSCs are performed by utilizing the cell counting and sorting modules. Experimental results show that a separation efficiency as high as 88% for HSCs from cord blood is achieved within 40 min for a sample volume of 100 mul. Therefore, the development of this integrated microfluidic system may be promising for various applications such as stem cell research and cell therapy.

Label free detection of CD4+ and CD8+ T cells using the optofluidic ring resonator

We have demonstrated label free detection of CD4+ and CD8+ T-Lymphocyte whole cells and CD4+ T-Lymphocyte cell lysis using the optofluidic ring resonator (OFRR) sensor. The OFRR sensing platform incorporates microfluidics and photonics in a setup that utilizes small sample volume and achieves a fast detection time. In this work, white blood cells were isolated from healthy blood and the concentrations were adjusted to match T-Lymphocyte levels of individuals infected with HIV. Detection was accomplished by immobilizing CD4 and CD8 antibodies on the inner surface of the OFRR. Sensing results show excellent detection of CD4+ and CD8+ T-Lymphocyte cells at medically significant concentrations with a detection time of approximately 30 minutes. This work will lead to a rapid and low-cost sensing device that can provide a CD4 and CD8 count as a measure of HIV progression.

Lensfree holographic imaging of antibody microarrays for high-throughput detection of leukocyte numbers and function

Characterization of leukocytes is an integral part of blood analysis and blood-based diagnostics. In the present paper, we combine lensless holographic imaging with antibody microarrays for rapid and multiparametric analysis of leukocytes from human blood. Monoclonal antibodies (Abs) specific for leukocyte surface antigens (CD4 and CD8) and cytokines (TNF-alpha, IFN-gamma, IL-2) were printed in an array so as to juxtapose cell capture and cytokine detection antibody (Ab) spots. Integration of Ab microarrays into a microfluidic flow chamber (4 muL volume) followed by incubation with human blood resulted in capture of CD4 and CD8 T-cells on specific Ab spots. On-chip mitogenic activation of these cells induced release of cytokine molecules that were subsequently captured on neighboring anticytokine Ab spots. The binding of IL-2, TNF-alpha, and IFN-gamma molecules on their respective Ab spots was detected using horseradish peroxidase (HRP)-labeled anticytokine Abs and a visible color reagent. Lensfree holographic imaging was then used to rapidly ( approximately 4 s) enumerate CD4 and CD8 T-lymphocytes captured on Ab spots and to quantify the cytokine signal emanating from IL-2, TNF-alpha, and IFN-gamma spots on the same chip. To demonstrate the utility of our approach for infectious disease monitoring, blood samples of healthy volunteers and human immunodeficiency virus (HIV)-infected patients were analyzed to determine the CD4/CD8 ratio, an important HIV/AIDS diagnostic marker. The ratio obtained by lensfree on-chip imaging of CD4 and CD8 T-cells captured on Ab spots was in close agreement with conventional microscopy-based cell counting. The present paper, describing tandem use of Ab microarrays and lensfree holographic imaging, paves the way for future development of miniature cytometry devices for multiparametric blood analysis at the point of care or in a resource-limited setting.

Lensless imaging for point-of-care testing

We show a platform that merges a microfluidic chip with lensless imaging for CD4(+) T-lymphocyte counting at resource-limited settings. To capture CD4(+) T lymphocytes, anti-CD4 antibody was immobilized on a microfluidic chip. The captured cells were detected by a charge coupled device (CCD) sensor using lensless shadow imaging techniques. Gray scale shadow images of captured cells on the chip (24 mm x 4 mm x 50 mum) were enumerated in three seconds using an automatic cell counting software. The device achieved 70.2 +/- 6.5% capture efficiency, 88.8 +/- 5.4% capture specificity for CD4(+) T-lymphocytes, 96 +/- 1.6% CCD efficiency, and 83.5 +/- 2.4% overall platform performance (n = 9 devices). This integrated platform has potential for point-of-care testing (POCT) to rapidly capture, image and count specific cell types from unprocessed whole blood.

A robust electrical microcytometer with 3-dimensional hydrofocusing

In this paper, we present a device to electrically count blood cell populations using an AC impedance interrogation technique in a microfabricated cytometer (microcytometer). Specifically, we direct our attention to obtaining the concentration of human CD4+ T lymphocytes (helper T cells), which is a necessary method to diagnose patients for HIV/AIDS and to give an accurate prognosis on the effectiveness of ARV (anti-retroviral) drug treatments. We study the effectiveness of a simple-to-fabricate 3-dimensional (3D) hydrodynamic focusing mechanism through fluidic simulations and corresponding experiments to increase the signal-to-noise ratio of impedance pulses caused by particle translocation and ensure lower variance in particle translocation height through the electrical sensing region. We found that the optimal 3D sheath flow settings result in a 44.4% increase in impedance pulse signal-to-noise ratio in addition to giving a more accurate representation of particle size distribution. Our microcytometer T cell counts closely with those found using an industry-standard flow cytometer for the concentration range of over three orders of magnitude and using a sample volume approximately the size of a drop of blood (approximately 20 microL). In addition, our device displayed the capability to differentiate between live and dead/dying lymphocyte populations. This microcytometer can be the basis of a portable, rapid, inexpensive solution to obtaining live/dead blood cell counts even in the most resource-poor regions of the world.

Integrating microfluidics and lensless imaging for point-of-care testing

We demonstrate an integrated platform that merges a microfluidic chip with lensless imaging to target CD4(+) T-lymphocyte counts for HIV point-of-care testing at resource-limited settings. The chips were designed and fabricated simply with a laser cutter without using expensive cleanroom equipment. To capture CD4(+) T-lymphocytes from blood, anti-CD4 antibody was immobilized on only one side of the microfluidic chip. These captured cells were detected through an optically clear chip using a charge coupled device (CCD) sensor by lensless shadow imaging techniques. Gray scale image of the captured cells in a 24 mm x 4 mm x 50 microm microfluidic chip was obtained by the lensless imaging platform. The automatic cell counting software enumerated the captured cells in 3s. Captured cells were also imaged with a fluorescence microscope and manually counted to characterize functionality of the integrated platform. The integrated platform achieved 70.2+/-6.5% capture efficiency, 88.8+/-5.4% capture specificity for CD4(+) T-lymphocytes, 96+/-1.6% CCD efficiency, and 83.5+/-2.4% overall platform performance (n=9 devices) compared to the gold standard, i.e. flow cytometry count. The integrated system gives a CD4 count from blood within 10 min. The integrated platform points a promising direction for point-of-care testing (POCT) to rapidly capture, image and count subpopulations of cells from blood samples in an automated matter.

Simultaneous particle counting and detecting on a chip

This paper reports a lab-on-a-chip device that performs particle detection and number counting by coupling the fluorescent detection and particle counting simultaneously. The particle number counting is realized by a resistive pulse sensor (RPS) and fluorescent particle detection is achieved by a miniaturized laser-fiber optic detection system. By using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the RPS signal-to-noise ratio is improved significantly. Two-stage differential amplification is used to further increase the signal-to-noise ratio for both the RPS and fluorescent signals. This method is also highly sensitive, so that we were able to realize the RPS and fluorescent detection of 0.9 microm (mean diameter) fluorescent particles. Excellent agreement was achieved by comparing the results obtained by our system with the results from a commercial flow cytometer for a variety of samples of mixed fluorescent and non-fluorescent particles. The method described in this paper is simple and can be applied to develop a compact device without the need of lock-in amplifier or similar bulky supplemental equipment.

Microfluidic differential resistive pulse sensors

This study demonstrates an on-chip resistive pulse-sensing scheme with a design of symmetric mirror channels, which significantly reduces the noise and achieves better signal-to-noise ratio. Polystyrene particles of different sizes have been detected with the developed sensing scheme and a record low volume ratio of the particle to the sensing channel, or 0.0004%, has been detected with particles of 520 nm in diameter in a sensing aperture of 50x16x20 microm3. This volume ratio is about ten times lower than the lowest volume ratio reported in the literature including that specified for commercial Coulter counters.