High-speed separation system of randomly suspended single living cells by laser trap and dielectrophoresis

Parallel Manipulation and Flexible Assembly of Micro-Spiral via Optoelectronic Tweezers

Micro-spiral has a wide range of applications in smart materials, such as drug delivery, deformable materials, and micro-scale electronic devices by utilizing the manipulation of electric fields, magnetic fields, and flow fields. However, it is incredibly challenging to achieve a massively parallel manipulation of the micro-spiral to form a particular microstructure in these conventional methods. Here, a simple method is reported for assembling micro-spirals into various microstructures via optoelectronic tweezers (OETs), which can accurately manipulate the micro-/bio-particles by projecting light patterns. The manipulation force of micro-spiral is analyzed and simulated first by the finite element simulation. When the micro-spiral lies at the bottom of the microfluidic chip, it can be translated or rotated toward the target position by applying control forces simultaneously at multiple locations on the long axis of the micro-spiral. Through the OET manipulation, the length of the micro-spiral chain can reach 806.45 μm. Moreover, the different parallel manipulation modes are achieved by utilizing multiple light spots. The results show that the micro-spirulina can be manipulated by a real-time local light pattern and be flexibly assembled into design microstructures by OETs, such as a T-shape circuit, link lever, and micro-coil pairs of devices. This assembly method using OETs has promising potential in fabricating innovative materials and microdevices for practical engineering applications.

Weakening of resistance force by cell-ECM interactions regulate cell migration directionality and pattern formation

Collective migration of epithelial cells is a fundamental process in multicellular pattern formation. As they expand their territory, cells are exposed to various physical forces generated by cell-cell interactions and the surrounding microenvironment. While the physical stress applied by neighbouring cells has been well studied, little is known about how the niches that surround cells are spatio-temporally remodelled to regulate collective cell migration and pattern formation. Here, we analysed how the spatio-temporally remodelled extracellular matrix (ECM) alters the resistance force exerted on cells so that the cells can expand their territory. Multiple microfabrication techniques, optical tweezers, as well as mathematical models were employed to prove the simultaneous construction and breakage of ECM during cellular movement, and to show that this modification of the surrounding environment can guide cellular movement. Furthermore, by artificially remodelling the microenvironment, we showed that the directionality of collective cell migration, as well as the three-dimensional branch pattern formation of lung epithelial cells, can be controlled. Our results thus confirm that active remodelling of cellular microenvironment modulates the physical forces exerted on cells by the ECM, which contributes to the directionality of collective cell migration and consequently, pattern formation.

Applications of Converged Various Forces for Detection of Biomolecules and Novelty of Dielectrophoretic Force in the Applications

Since separation of target biomolecules is a crucial step for highly sensitive and selective detection of biomolecules, hence, various technologies have been applied to separate biomolecules, such as deoxyribonucleic acid (DNA), protein, exosome, virus, etc. Among the various technologies, dielectrophoresis (DEP) has the significant advantage that the force can provide two different types of forces, attractive and repulsive DEP force, through simple adjustment in frequency or structure of microfluidic chips. Therefore, in this review, we focused on separation technologies based on DEP force and classified various separation technologies. First, the importance of biomolecules, general separation methods and various forces including DEP, electrophoresis (EP), electrothermal flow (ETF), electroosmosis (EO), magnetophoresis, acoustophoresis (ACP), hydrodynamic, etc., was described. Then, separating technologies applying only a single DEP force and dual force, moreover, applying other forces simultaneously with DEP force were categorized. In addition, advanced technologies applying more than two different kinds of forces, namely complex force, were introduced. Overall, we critically reviewed the state-of-the-art of converged various forces for detection of biomolecules with novelty of DEP.

Current Trends of Microfluidic Single-Cell Technologies

The investigation of human disease mechanisms is difficult due to the heterogeneity in gene expression and the physiological state of cells in a given population. In comparison to bulk cell measurements, single-cell measurement technologies can provide a better understanding of the interactions among molecules, organelles, cells, and the microenvironment, which can aid in the development of therapeutics and diagnostic tools. In recent years, single-cell technologies have become increasingly robust and accessible, although limitations exist. In this review, we describe the recent advances in single-cell technologies and their applications in single-cell manipulation, diagnosis, and therapeutics development.

A membrane-anchored aptamer sensor for probing IFNγ secretion by single cells

Insight into the behavior of individual immune cells, in particular cytokine secretion, will contribute to a more fundamental understanding of the immune system. In this work, we have developed a cell membrane-anchored sensor for the detection of cytokines secreted by single cells using a combination of aptamer-based sensors and droplet microfluidics.

Dielectrophoretic Relay Assisted Molecular Communication for In-Sequence Molecule Delivery

With current research focus to interconnect the molecular communication environment with external environment, it is imperative to design external devices working on molecular communication schemes to be interfaced with in-vivo molecular network. Recently, efforts have been made to integrate molecular communication with Lab-on-chip (LOC); one of the techniques used in LOC for manipulation and transportation of molecules is Dielctrophoresis (DEP). We propose the use of DEP in molecular communication to maintain in-sequence delivery of molecules. DEP planar electrodes are modeled as relays used in telecommunications. We describe the theoretical system model and analyze the effect of introducing DEP relays in diffusive channel in terms of probability of in-sequence delivery of molecules. Information rate of DEP-based channel is analytically obtained for in-sequence delivery. The numerical results obtained show that the information rate for in-sequence delivery of molecules through diffusive channel increases by 26% if DEP relays are used in the channel. Though the system is sensitive to noise variance, incorporation of DEP relay results in a substantial improvement in the capacity of the channel.

Virus enrichment for single virus infection by using 3D insulator based dielectrophoresis

We developed an active virus filter (AVF) that enables virus enrichment for single virus infection, by using insulator-based dielectrophoresis (iDEP). A 3D-constricted flow channel design enabled the production of an iDEP force in the microfluidic chip. iDEP using a chip with multiple active virus filters (AVFs) was more accurate and faster than using a chip with a single AVF, and improved the efficiency of virus trapping. We utilized maskless photolithography to achieve the precise 3D gray-scale exposure required for fabrication of constricted flow channel. Influenza virus (A PR/8) was enriched by a negative DEP force when sinusoidal wave was applied to the electrodes within an amplitude range of 20 Vp-p and a frequency of 10 MHz. AVF-mediated virus enrichment can be repeated simply by turning the current ON or OFF. Furthermore, the negative AVF can inhibit virus adhesion onto the glass substrate. We then trapped and transported one of the enriched viruses by using optical tweezers. This microfluidic chip facilitated the effective transport of a single virus from AVFs towards the cell-containing chamber without crossing an electrode. We successfully transported the virus to the cell chamber (v = 10 µm/s) and brought it infected with a selected single H292 cell.

Microfluidic platforms for single-cell protein analysis

Elucidation of the heterogeneity of cells is a challenging task due to the lack of efficient analytical tools to make measurements with single-cell resolution. Microfluidics has emerged as a powerful platform for single-cell analysis with the ability to manipulate small volume and integrate multiple sample preparation steps into one device. In this review, we discuss the differentiating advantages of microfluidic platforms that have been demonstrated for single-cell protein analysis.

Enhanced cell sorting and manipulation with combined optical tweezer and microfluidic chip technologies

Sorting (or isolation) and manipulation of rare cells with high recovery rate and purity are of critical importance to a wide range of physiological applications. In the current paper, we report on a generic single cell manipulation tool that integrates optical tweezers and microfluidic chip technologies for handling small cell population sorting with high accuracy. The laminar flow nature of microfluidics enables the targeted cells to be focused on a desired area for cell isolation. To recognize the target cells, we develop an image processing methodology with a recognition capability of multiple features, e.g., cell size and fluorescence label. The target cells can be moved precisely by optical tweezers to the desired destination in a noninvasive manner. The unique advantages of this sorter are its high recovery rate and purity in small cell population sorting. The design is based on dynamic fluid and dynamic light pattern, in which single as well as multiple laser traps are employed for cell transportation, and a recognition capability of multiple cell features. Experiments of sorting yeast cells and human embryonic stem cells are performed to demonstrate the effectiveness of the proposed cell sorting approach.

Dielectrophoretic capture of E. coli cells at micropatterned nanoelectrode arrays

This paper reports capture and detection of pathogenic bacteria based on AC dielectrophoresis (DEP) and electrochemical impedance spectroscopy (EIS) employing an embedded vertically aligned carbon nanofiber (VACNF) nanoelectrode array (NEA) versus a macroscopic indium-tin-oxide (ITO) transparent electrode in "points-and-lid" configuration. The nano-DEP device was fabricated using photolithography processes to define an exposed active region on a randomly distributed NEA and a microfluidic channel on ITO to guide the flow of labeled Escherichia coli cells, respectively, and then bond them into a fluidic chip. A high-frequency (100 kHz) AC field was applied to generate positive DEP at the tips of exposed CNFs. Enhanced electric field gradient was achieved due to reduction in electrode size down to nanometer scale which helped to overcome the large hydrodynamic drag force experienced by E. coli cells at high flow velocities (up to 1.6 mm/s). This DEP device was able to effectively capture a significant number of E. coli cells. Significant decrease in the absolute impedance at the NEA was observed in EIS experiments. The results obtained in this study suggest the possibility of integration of a fully functional electronic device for rapid, reversible and label-free capture and detection of pathogenic bacteria.

Development and characterization of a microfluidic chamber incorporating fluid ports with active suction for localized chemical stimulation of brain slices

We report a novel microfluidic chamber incorporating fluid ports with active suction to achieve localized chemical stimulation of brain slices. A two-level soft-lithography process is used to fabricate fluid ports with integrated injection and suction holes that are connected to underlying microchannels. Fluorescence imaging, particle tracking velocimetry, and cell staining are used to characterize flows around a fluid port with or without active suction to validate effective localization of injected chemicals. To demonstrate biological applicability of the chamber, we show an induction of cortical spreading depression (CSD) waves in mouse brain slices through controlled focal delivery of potassium chloride solution.

On-Chip Particle Sorting into Multiple Channels by Magnetically Driven Microtools

This paper presents a new type of sorting system by magnetic microtools (MMT) separating particles into multiple channels. Two nickel-based MMTs are activated by commercially available permanent magnets below the biochip to lead particles to certain channels via fluid force. The horizontally assembled permanent magnet drive we developed shows that the MMT positioning accuracy had been improved 5 times in 2 degrees of freedom. The channel and the MMT shape are determined based on FEM analysis to ensure that particles flow smoothly. We have successfully achieved to sort 100 µm diameter microbeads into 7 branched channels. The noncontact drive and disposable chip provide a less invasive environment for the cell with low cost.

Exploitation of physical and chemical constraints for three-dimensional microtissue construction in microfluidics

There are a plethora of approaches to construct microtissues as building blocks for the repair and regeneration of larger and complex tissues. Here we focus on various physical and chemical trapping methods for engineering three-dimensional microtissue constructs in microfluidic systems that recapitulate the in vivo tissue microstructures and functions. Advances in these in vitro tissue models have enabled various applications, including drug screening, disease or injury models, and cell-based biosensors. The future would see strides toward the mesoscale control of even finer tissue microstructures and the scaling of various designs for high throughput applications. These tools and knowledge will establish the foundation for precision engineering of complex tissues of the internal organs for biomedical applications.

Size-Dependent Filtration and Trapping of Microparticles in a Microfluidic Chip Using Graduated Gaps and Centrifugal Force

We proposed size-dependent microparticle filtration and trapping using graduated microchannel gaps and centrifugal force using a three-dimensional magnetically driven microtool (3D-MMT) in a microfluidic chip made of polydimethylsiloxane (PDMS). Our paper contributes the following to the field: (1) Particle filtration is robust against pressure fluctuation due to tube vibration between the chip and pump. (2) Clogging by microparticles is avoided by rotating the 3D-MMT in a microchamber. (3) Size-classified microparticles are trapped by flow control along microchannel gaps. Different-sized microparticles flow in spiral microchannels and are filtered based on size between gaps and the substrate by centrifugal force. Microparticles larger than gaps remain in the inner microchannel. Rotating the 3D-MMT using an external magnetic circuit generates swirling flow in the microchamber. Size-classified microparticles are trapped in microchannels by closing the drain port for the targeted particle. Trapped particles are measured by direct observation and treated by reagent. After experiments, trapped particles are extracted by opening drain ports. We demonstrated microparticle filtration and microparticle trapping in the microfluidic chip.

A simple microfluidic method to select, isolate, and manipulate single-cells in mechanical and biochemical assays

This article describes a simple and low-tech microfluidic method for single-cell experimentation, which permits cell selection without stress, cell manipulation with fine control, and passive self-exclusion of all undesired super-micronic particles. The method requires only conventional soft lithography microfabrication techniques and is applicable to any microfluidic single-cell circuitry. The principle relies on a bypass plugged in parallel with a single-cell assay device and collecting 97% of the flow rate. Cell selection into the single cell device is performed by moving the cell of interest back and forth in the vicinity of the junction between the bypass and the analysis circuitry. Cell navigation is finely controlled by hydrostatic pressure via centimetre-scale actuation of external macroscopic reservoirs connected to the device. We provide successful examples of biomechanical and biochemical assays on living human leukocytes passing through 4 mum wide capillaries. The blebbing process dynamics are monitored by conventional 24 fps videomicroscopy and subcellular cytoskeleton organization is imaged by on-chip immunostaining.

Optimization of microfluidic single cell trapping for long-term on-chip culture

The poor efficiency of microfluidic single cell trapping is currently restricting the full potential of state-of-the-art single cell analyses. Using fluid dynamics simulations in combination with particle image velocimetry to systematically optimize trap architectures, we present a microfluidic chip with enhanced single cell trapping and on-chip culture performance. Upon optimization of trap geometries, we measured trapping efficiencies of up to 97%. Our device also enables the stable, relatively long-term culture of individual non-adherent mammalian cells in high-throughput without a significant decrease in cell viability. As a first application of this platform we demonstrate the automated separation of the two daughter cells generated upon single cell division. The reliable trapping and re-trapping of mammalian cells should for example provide the fundament for novel types of investigations in stem cell and tumour cell biology, which depend on reliable tracking of genealogical relationships such as in stem cell lineage tracking.

Magnetically Driven Microtools Actuated by a Focused Magnetic Field for Separating of Microparticles

We succeeded in reducing magnetic interaction region with a focused magnetic field on-chip. Novelty of this paper is summarized as follows. (1) We used neodymium powder as the main component of magnetically driven microtools (MMT). The density of magnetic flux was improved by about 100 times after magnetization. (2) We fabricated a couple of pin mounted under a microfluidic chip. The density of magnetic flux was improved by about 1.8 times. As a result, the density of magnetic flux had a single peak using the pin, unlike in a setup without pins. It was confirmed that the size of the magnetic interaction region for the current setting was one twentieth that of the previous setting.

Simple, fast and high-throughput single-cell analysis on PDMS microfluidic chips

This paper demonstrated the chemical analysis of single cell on a cross PDMS microfluidic chip in a simple, fast, and high-throughput mode. The pre-stained cells were sequentially loaded into the cross section by hydrodynamic force, lysed by 0.2% SDS and subsequently the lysates were detected by LIF. Each cell can be lysed within 500 ms due to its high concentration of SDS at cross section resulted from the absence of electroosmosis after surface coating in microchannel. The reliability and quality of the analysis was confirmed by analysis of glutathione and rhodamine 123 in single K562 cells. In each run, approximately 100 cells could be analyzed in about 10 min, which demonstrated the comparatively high throughput. The proposed microfluidic method is simple, fast, and high throughput, which might be of significance in identifying the biological molecules involved in fast biochemical processes and studying heterogenous cells.

Synergism between particle-based multiplexing and microfluidics technologies may bring diagnostics closer to the patient

In the field of medical diagnostics there is a growing need for inexpensive, accurate, and quick high-throughput assays. On the one hand, recent progress in microfluidics technologies is expected to strongly support the development of miniaturized analytical devices, which will speed up (bio)analytical assays. On the other hand, a higher throughput can be obtained by the simultaneous screening of one sample for multiple targets (multiplexing) by means of encoded particle-based assays. Multiplexing at the macro level is now common in research labs and is expected to become part of clinical diagnostics. This review aims to debate on the “added value” we can expect from (bio)analysis with particles in microfluidic devices. Technologies to (a) decode, (b) analyze, and (c) manipulate the particles are described. Special emphasis is placed on the challenges of integrating currently existing detection platforms for encoded microparticles into microdevices and on promising microtechnologies that could be used to down-scale the detection units in order to obtain compact miniaturized particle-based multiplexing platforms.

Optofluidic trapping and transport on solid core waveguides within a microfluidic device

In this work we demonstrate an integrated microfluidic/photonic architecture for performing dynamic optofluidic trapping and transport of particles in the evanescent field of solid core waveguides. Our architecture consists of SU-8 polymer waveguides combined with soft lithography defined poly(dimethylsiloxane) (PDMS) microfluidic channels. The forces exerted by the evanescent field result in both the attraction of particles to the waveguide surface and propulsion in the direction of optical propagation both perpendicular and opposite to the direction of pressure-driven flow. Velocities as high as 28 mum/s were achieved for 3 mum diameter polystyrene spheres with an estimated 53.5 mW of guided optical power at the trapping location. The particle-size dependence of the optical forces in such devices is also characterized.

In-Situ Formation of a Gel Microbead for Laser Micromanipulation of Microorganisms, DNA, and Viruses

We proposein situformation of gel microbeads made of a thermoreversible hydrogel for indirect laser micromanipulation of microorganisms, DNA, and viruses. Using a 1064 nm laser, we irradiated an aqueous solution mixed with poly-(N-isopropylacrylamide) through a high- magnification lens, thereby forming a gel microbead through heating at the laser focus. The gel microbead, trapped by the laser, was used to indirectly manipulate micro- and nano-scale samples. Laser tweezers stably handle micro-scale object ranging from several tens of nm to several hundreds of µm. This cannot be done with nano-scale objects of a few nm, however, due to laser beam heating. We demonstrate how to manipulate microorganisms, DNA, and viruses indirectly using a gel microbead made from an aqueous poly-(N-isopropylacrylamide) solution. We reduced laser power for gel microbead formation, and used the gel microbead trapped by the laser to manipulate microorganisms, DNA, and viruses.

Miniaturized high-NA focusing-mirror multiple optical tweezers

An array of high numerical aperture parabolic micromirrors (NA = 0.96) is used to generate multiple optical tweezers and to trap micron-sized dielectric particles in three dimensions within a fluidic device. The array of micromirrors allows generating arbitrarily large numbers of 3D traps, since the whole trapping area is not restricted by the field-of-view of the high-NA microscope objectives used in traditional tweezers arrangements. Trapping efficiencies of Q(max) r approximately = 0.22, comparable to those of conventional tweezers, have been measured. Moreover, individual fluorescence light from all the trapped particles can be collected simultaneously with the high-NA of the micromirrors. This is demonstrated experimentally by capturing more than 100 fluorescent micro-beads in a fluidic environment. Micromirrors may easily be integrated in microfluidic devices, offering a simple and very efficient solution for miniaturized optical traps in lab-on-a-chip devices.

The combination of optical tweezers and microwell array for cells physical manipulation and localization in microfluidic device

A microfluidic device combined with the microwell array and optical tweezers was set up for cell manipulation, localization and cultivation. Yeast cells were manipulated by a 1,064 nm laser and transferred to microwell array as a demonstration. The flow velocities at which the yeast cell can be confined in microwells of different sizes are characterized. The simulation of the cell's flow trace in the microwell at different flow velocities is consisting with our experiment result. And we also proved a trapping laser power of 0.30 W is harmless for yeast cell cultivation. As a simple approach, this method can push forward the cell cultivation, cell interaction and other cell biology or biomedical studies in microfluidic system.

Theoretical and experimental studies on filtering tumor cells from blood cell mixtures with dam structure in microfluidic devices

Here, a filter with series of pools and dams structures was designed and fabricated, utilizing size difference between tumor and blood cells. The cell mixtures were successfully filtrated out by the filter, and separation efficiency was up to 99.9%. To evaluate the filter, physical models were made to describe the behaviors of different cells in microfluidic systems. As the ability of cell deformation depends on both cells' size and excess surface index (ESI), we measured the excess membrane area of different cells, and got tumor cell's ESI is 61.7% ~ 81% comparing with red blood cell (RBC) (44%) and white blood cell (WBC) (84%~137%). Then from the formulas we deduced, we get the filtering limitations of RBC, WBC, and tumor cell are respectively, around 1.8μm, 1.0-1.6μm and 3.7-4.4μm for dam structure; and 1.3μm, 0.9-1.3μm and 3-3.4μm radius for pipes, which actually show conditions for separation. The accuracy and high flux of the filter provide possibilities to isolate cancer cells directly from the blood in real-time, which could become a potential therapy to cancers.

Designing a nano-interface in a microfluidic chip to probe living cells: challenges and perspectives

Nanotechnology-based materials are beginning to emerge as promising platforms for biomedical analysis, but measurement and control at the cell-chip interface remain challenging. This idea served as the basis for discussion in a focus group at the recent National Academies Keck Futures Initiative. In this Perspective, we first outline recent advances and limitations in measuring nanoscale mechanical, biochemical, and electrical interactions at the interface between biomaterials and living cells. Second, we present emerging experimental and conceptual platforms for probing living cells with nanotechnology-based tools in a microfluidic chip. Finally, we explore future directions and critical needs for engineering the cell-chip interface to create an integrated system capable of high-resolution analysis and control of cellular physiology.

Cell handling using microstructured membranes

Gentle and precise handling of cell suspensions is essential for scientific research and clinical diagnostic applications. Although different techniques for cell analysis at the micro-scale have been proposed, many still require that preliminary sample preparation steps be performed off the chip. Here we present a microstructured membrane as a new microfluidic design concept, enabling the implementation of common sample preparation procedures for suspensions of eukaryotic cells in lab-on-a-chip devices. We demonstrate the novel capabilities for sample preparation procedures by the implementation of metered sampling of nanoliter volumes of whole blood, concentration increase up to three orders of magnitude of sparse cell suspension, and circumferentially uniform, sequential exposure of cells to reagents. We implemented these functions by using microstructured membranes that are pneumatically actuated and allowed to reversibly decouple the flow of fluids and the displacement of eukaryotic cells in suspensions. Furthermore, by integrating multiple structures on the same membrane, complex sequential procedures are possible using a limited number of control steps.

On chip single-cell separation and immobilization using optical tweezers and thermosensitive hydrogel

A novel approach appropriate for rapid separation and immobilization of a single cell by concomitantly utilizing laser manipulation and locally thermosensitive hydrogelation is proposed in this paper. We employed a single laser beam as optical tweezers for separating a target cell and locating it adjacent to a fabricated, transparent micro heater. Simultaneously, the target cell is immobilized or partially entrapped by heating the thermosensitive hydrogel with the micro heater. The state of the thermosensitive hydrogel can be switched from sol to gel and gel to sol by controlling the temperature through heating and cooling by the micro heater. After other unwanted cells are removed by the high-speed cleaning flow in the microchannel, the entrapped cell is successfully isolated. It is possible to collect the immobilized target cell for analysis or culture by switching off the micro heater and releasing the cell from the entrapment. We demonstrated that the proposed approach is feasible for rapid manipulation, immobilization, cleaning, isolation and extraction of a single cell. The experimental results are shown here.

Microfluidic devices for the analysis of apoptosis

Apoptosis is the outcome of a metabolic cascade that results in cell death in a controlled manner. Due to its important role in maintaining balance in organisms, in mechanisms of diseases, and tissue homeostasis, apoptosis is of great interest in the emerging fields of systems biology. Research into cell death regulation and efforts to model apoptosis processes have become powerful drivers for new technologies to acquire ever more comprehensive information from cells and cell populations. The microfluidic technology promises to integrate and miniaturize many bioanalytical processes, which offers an alternative platform for the analysis of apoptosis. This review aims to highlight the recent developments of microfluidic devices in measuring the hallmarks as well as the dynamic process of cellular apoptosis. The potential capability and an outlook of microfluidic devices for the study of apoptosis are addressed.

Microfabrication and Laser Manipulation of Functional Microtool Using In-Situ Photofabrication

Single cell experiments have become very important for investigating unknown cell properties. We developed a novel technique to study individual cell properties on a chip using newly developed cell manipulation by laser tweezers with the photo-crosslinkable resin, using this resin to developed functional colored, fluorescent, cell binding, rotation free, and rope shaped microtools on a chip. Colored and fluorescent microtools are for cell manipulation using inexpensive image processing. Cell binding microtools are for high-speed transport of target cells. Rotation free microtools are for attitude control and precise force measurement of cells and DNA. Rope shaped microtools are for versatile manipulation. Laser tweezers is used to position-control microtools. We used a mercury lamp for UV illumination at the local area for combining microtools and fabricated our functional microtools and manipulated cells on the microchip.

Microfluidics for flow cytometric analysis of cells and particles

This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles. The high-speed analytical capabilities of flow cytometry depend on the cooperative use of microfluidics, optics and electronics. Along with the improvement of other components, replacement of conventional glass capillary-based fluidics with microfluidic sample handling systems operating in microfabricated structures enables volume- and power-efficient, inexpensive and flexible analysis of particulate samples. In this review, we present various efforts that take advantage of novel microscale flow phenomena and microfabrication techniques to build microfluidic cell analysis systems.

Immobilization of individual cells by local photo-polymerization on a chip

A novel separation method for random screening of target cells from a large heterogeneous population by using a local photo-polymerization is developed. A photo-crosslinkable resin solution is mixed with the sample liquid and we controlled the state from sol to gel by irradiating the near ultraviolet (UV) light with the mercury lamp and He-Cd laser near the target cell. We applied three types of immobilization methods such as direct immobilization method, caging method, and direct immobilization with position control method. The selected cell is immobilized in the cured resin directly or inside the cage of the cured resin. In the position control method, laser tweezers are employed to manipulate the target cell indirectly by using the droplet of the resin as a microtool. The cell is positioned properly by the laser manipulation system and is immobilized in the polymerized resin. After the selected cells are immobilized we can easily remove the other objects by the cleaning flow in the microchannel since the polymerized resin strongly binds with the cover glass and resists more than 466 mm s(-1) flow speed in the microchannel (microchannel size: width is 500 micron and depth is 100 micron). We tested the mercury lamp as well as the He-Cd laser for UV-light irradiation at the local area and confirmed improvement of resolution of the cured area by using the He-Cd laser (from 7 micron to 5 micron). Based on this method, we succeeded in single cell immobilization and basic experiments such as culture and fluorescent dyeing of immobilized yeast cells.

Microtechnologies and nanotechnologies for single-cell analysis

Many efforts are currently underway to try and mimic the properties of single cells with the aim of designing chips that are as efficient as cells. However, cells are nature's nanotechnology engineering at the scale of atoms and molecules, and it might be better to envision a microchip that utilizes a single cell as an experimentation platform. A novel, so-called laboratory-in-a-cell concept has been described, where advantage is taken of micro- and nanotechnological tools to enable precise control of the biochemical cellular environment; these tools also offer the possibility to analyse the composition of single cells. Methods for single-cell handling and analysis are being developed and will be required for this concept to progress further.

Microfabricated System for Parallel Single-Cell Capillary Electrophoresis

Performing single-cell electrophoresis separations using multiple parallel microchannels offers the possibility of both increasing throughput and eliminating cross-contamination between different separations. The instrumentation for such a system requires spatial and temporal control of both single-cell selection and lysis. To address these problems, a compact platform is presented for single-cell capillary electrophoresis in parallel microchannels that combines optical tweezers for cell selection and electromechanical lysis. Calcein-labeled acute myloid leukemia (AML) cells were selected from an on-chip reservoir and transported by optical tweezers to one of four parallel microfluidic channels. Each channel entrance was manufactured by F2-laser ablation to form a 20- to 10-microm tapered lysis reservoir, creating an injector geometry effective in confining the cellular contents during mechanical shearing of the cell at the 10-microm capillary entrance. The contents of individual cells were simultaneously injected into parallel channels resulting in electrophoretic separation as recorded by laser-induced fluorescence of the labeled cellular contents.

Microfluidic device for single-cell analysis

We have developed a novel microfluidic device constructed from poly(dimethylsiloxane) using multilayer soft lithography technology for the analysis of single cells. The microfluidic network enables the passive and gentle separation of a single cell from the bulk cell suspension, and integrated valves and pumps enable the precise delivery of nanoliter volumes of reagents to that cell. Various applications are demonstrated, including cell viability assays, ionophore-mediated intracellular Ca2+ flux measurements, and multistep receptor-mediated Ca2+ measurements. These assays, and others, are achieved with significant improvements in reagent consumption, analysis time, and temporal resolution over macroscale alternatives.

Hydrodynamic Micromanipulation of Individual Cells onto Patterned Attachment Sites on Biomicroelectromechanical System Chips

We report on a simple methodology to move selected single live cells to a desired location on a flat substrate, such as a patterned biomicroelectromechanical system chip. A macroscopic syringe-and-tube-based hydrodynamic manipulation system is used to achieve controlled cell navigation onto hydrophilic sites for cell attachment. Centimeter-per-second flow velocities generated by the system get downgraded to micrometers-per-second flow at the height of settled cells as a result of viscous flow in the medium. By pushing/pulling two syringes that produce two orthogonal flows, fine manipulation in any horizontal direction is feasible. After attachment of the desired cell(s) onto the selected hydrophilic site, all other unwanted cells are washed away from the surrounding hydrophobic surface with faster flow. This simple methodology is applicable for rapid cell pattern formation with high precision.

Lab-on-a-chip for drug development

Significant advances have been made in the development of micro-scale technologies for biomedical and drug discovery applications. The first generation of microfluidics-based analytical devices have been designed and are already functional. Microfluidic devices offer unique advantages in sample handling, reagent mixing, separation, and detection. We introduce and review microfluidic concepts, microconstruction techniques, and methods such as flow-injection analysis, electrokinesis, and cell manipulation. Advances in micro-device technology for proteomics, sample preconditioning, immunoassays, electrospray ionization mass spectrometry, and polymerase chain reaction are also reviewed.