Single-Cell Chemical Lysis in Picoliter-Scale Closed Volumes Using a Microfabricated Device

Sample preparation and detection methods in point-of-care devices towards future at-home testing

Timely and accurate diagnosis is critical for effective healthcare, yet nearly half the global population lacks access to basic diagnostics. Point-of-care (POC) testing offers partial solutions by enabling low-cost, rapid diagnosis at the patient's location. At-home POC devices have the potential to advance preventive care and early disease detection. Nevertheless, effective sample preparation and detection methods are essential for accurate results. This review surveys recent advances in sample preparation and detection methods at POC. The goal is to provide an in-depth understanding of how these technologies can enhance at-home POC devices. Lateral flow assays, nucleic acid tests, and virus detection methods are at the forefront of POC diagnostic technology, offering rapid and sensitive tools for identifying and measuring pathogens, biomarkers, and viral infections. By illuminating cutting-edge research on assay development for POC diagnostics, this review aims to accelerate progress towards widely available, user-friendly, at-home health monitoring tools that empower individuals in personalized healthcare in the future.

Recent advances in microfluidics for single-cell functional proteomics

Single-cell proteomics (SCP) reveals phenotypic heterogeneity by profiling individual cells, their biological states and functional outcomes upon signaling activation that can hardly be probed via other omics characterizations. This has become appealing to researchers as it enables an overall more holistic view of biological details underlying cellular processes, disease onset and progression, as well as facilitates unique biomarker identification from individual cells. Microfluidic-based strategies have become methods of choice for single-cell analysis because they allow facile assay integrations, such as cell sorting, manipulation, and content analysis. Notably, they have been serving as an enabling technology to improve the sensitivity, robustness, and reproducibility of recently developed SCP methods. Critical roles of microfluidics technologies are expected to further expand rapidly in advancing the next phase of SCP analysis to reveal more biological and clinical insights. In this review, we will capture the excitement of the recent achievements of microfluidics methods for both targeted and global SCP, including efforts to enhance the proteomic coverage, minimize sample loss, and increase multiplexity and throughput. Furthermore, we will discuss the advantages, challenges, applications, and future prospects of SCP.

New horizons in developing cell lysis methods: A Review

Cell lysis is an essential step in many studies related to biology and medicine. Based on the scale and medium that cell lysis is carried out, there are three main types of the cell lysis: 1) lysis of the cells in the surrounding environment, 2) lysis of the isolated or cultured cells and 3) Single cell lysis. Conventionally, several cell lysis methods have been developed, such as freeze-thawing, bead beating, incursion in liquid nitrogen, sonication and enzymatic and chemical based approaches. In recent years, various novel technologies have been employed to develop new methods of cell lysis. The aim of studies in this field is to introduce more precise and efficient tools or to reduce the costs of cell lysis procedures. Nanostructure based lysis methods, acoustic oscillation, electrical current, irradiation, bacteria-mediated cell lysis, magnetic ionic liquids, bacteriophage genes, monolith columns, hydraulic forces and steam explosion are some examples of new developed cell lysis methods. Beside the significant advances in this field, there are still many challenges and the tools must be further improved. This article is protected by copyright. All rights reserved.

Advanced tools and methods for single-cell surgery

Highly precise micromanipulation tools that can manipulate and interrogate cell organelles and components must be developed to support the rapid development of new cell-based medical therapies, thereby facilitating in-depth understanding of cell dynamics, cell component functions, and disease mechanisms. This paper presents a literature review on micro/nanomanipulation tools and their control methods for single-cell surgery. Micromanipulation methods specifically based on laser, microneedle, and untethered micro/nanotools are presented in detail. The limitations of these techniques are also discussed. The biological significance and clinical applications of single-cell surgery are also addressed in this paper.

Review of Microfluidic Methods for Cellular Lysis

Cell lysis is a process in which the outer cell membrane is broken to release intracellular constituents in a way that important information about the DNA or RNA of an organism can be obtained. This article is a thorough review of reported methods for the achievement of effective cellular boundaries disintegration, together with their technological peculiarities and instrumental requirements. The different approaches are summarized in six categories: chemical, mechanical, electrical methods, thermal, laser, and other lysis methods. Based on the results derived from each of the investigated reports, we outline the advantages and disadvantages of those techniques. Although the choice of a suitable method is highly dependent on the particular requirements of the specific scientific problem, we conclude with a concise table where the benefits of every approach are compared, based on criteria such as cost, efficiency, and difficulty.

On-chip protein separation with single-molecule resolution

Accurate identification of both abundant and rare proteins hinges on the development of single-protein sensing methods. Given the immense variation in protein expression levels in a cell, separation of proteins by weight would improve protein classification strategies. Upstream separation facilitates sample binning into smaller groups while also preventing sensor overflow, as may be caused by highly abundant proteins in cell lysates or clinical samples. Here, we scale a bulk analysis method for protein separation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), to the single-molecule level using single-photon sensitive widefield imaging. Single-molecule sensing of the electrokinetically moving proteins is achieved by in situ polymerization of the PAGE in a low-profile fluidic channel having a depth of only ~ 0.6 µm. The polyacrylamide gel restricts the Brownian kinetics of the proteins, while the low-profile channel ensures that they remain in focus during imaging, allowing video-rate monitoring of single-protein migration. Calibration of the device involves separating a set of Atto647N-covalently labeled recombinant proteins in the size range of 14-70 kDa, yielding an exponential dependence of the proteins' molecular weights on the measured mobilities, as expected. Subsequently, we demonstrate the ability of our fluidic device to separate and image thousands of proteins directly extracted from a human cancer cell line. Using single-particle image analysis methods, we created detailed profiles of the separation kinetics of lysine and cysteine -labeled proteins. Downstream coupling of the device to single-protein identification sensors may provide superior protein classification and improve our ability to analyze complex biological and medical protein samples.

Fully Automated Lab-On-A-Disc Platform for Loop-Mediated Isothermal Amplification Using Micro-Carbon-Activated Cell Lysis

Fast and fully automated deoxyribonucleic acid (DNA) amplification methods are of interest in the research on lab-on-a-disc (LOD) platforms because of their full compatibility with the spin-column mechanism using centrifugal force. However, the standard procedures followed in DNA amplification require accurate noncontact temperature control as well as cell lysis at a low temperature to prevent damage to the LOD platform. This requirement makes it challenging to achieve full automation of DNA amplification on an LOD. In this paper, a fully automated LOD capable of performing cell lysis and amplification on a single compact disc of DNA samples is proposed. The proposed system uses micro-carbon to heat DNA samples without damaging the LOD as well as a noncontact heating system and an infrared camera sensor to remotely measure the real temperature of the amplification chamber. Compared with conventional DNA amplification systems, the proposed system has the advantage of full automation of the LOD platform. Experimental results demonstrated that the proposed system offers a stable heating method for DNA amplification and cell lysis.

Sequencing of human genomes extracted from single cancer cells isolated in a valveless microfluidic device

Sequencing the genomes of individual cells enables the direct determination of genetic heterogeneity amongst cells within a population. We have developed an injection-moulded valveless microfluidic device in which single cells from colorectal cancer derived cell lines (LS174T, LS180 and RKO) and fresh colorectal tumors have been individually trapped, their genomes extracted and prepared for sequencing using multiple displacement amplification (MDA). Ninety nine percent of the DNA sequences obtained mapped to a reference human genome, indicating that there was effectively no contamination of these samples from non-human sources. In addition, most of the reads are correctly paired, with a low percentage of singletons (0.17 ± 0.06%) and we obtain genome coverages approaching 90%. To achieve this high quality, our device design and process shows that amplification can be conducted in microliter volumes as long as the lysis is in sub-nanoliter volumes. Our data thus demonstrates that high quality whole genome sequencing of single cells can be achieved using a relatively simple, inexpensive and scalable device. Detection of genetic heterogeneity at the single cell level, as we have demonstrated for freshly obtained single cancer cells, could soon become available as a clinical tool to precisely match treatment with the properties of a patient's own tumor.

Lab-on-a-Disc Platform for Automated Chemical Cell Lysis

Chemical cell lysis is an interesting topic in the research to Lab-on-a-Disc (LOD) platforms on account of its perfect compatibility with the centrifugal spin column format. However, standard procedures followed in chemical cell lysis require sophisticated non-contact temperature control as well as the use of pressure resistant valves. These requirements pose a significant challenge thereby making the automation of chemical cell lysis on an LOD extremely difficult to achieve. In this study, an LOD capable of performing fully automated chemical cell lysis is proposed, where a combination of chemical and thermal methods has been used. It comprises a sample inlet, phase change material sheet (PCMS)-based temperature sensor, heating chamber, and pressure resistant valves. The PCMS melts and solidifies at a certain temperature and thus is capable of indicating whether the heating chamber has reached a specific temperature. Compared to conventional cell lysis systems, the proposed system offers advantages of reduced manual labor and a compact structure that can be readily integrated onto an LOD. Experiments using Salmonella typhimurium strains were conducted to confirm the performance of the proposed cell lysis system. The experimental results demonstrate that the proposed system has great potential in realizing chemical cell lysis on an LOD whilst achieving higher throughput in terms of purity and yield of DNA thereby providing a good alternative to conventional cell lysis systems.

Efficient analysis of a small number of cancer cells at the single-cell level using an electroactive double-well array

Analysis of the intracellular materials of a small number of cancer cells at the single-cell level is important to improve our understanding of cellular heterogeneity in rare cells. To analyze an extremely small number of cancer cells (less than hundreds of cells), an efficient system is required in order to analyze target cells with minimal sample loss. Here, we present a novel approach utilizing an advanced electroactive double-well array (EdWA) for on-chip analysis of a small number of cancer cells at the single-cell level with minimal loss of target cells. The EdWA consisted of cell-sized trap-wells for deterministic single-cell trapping using dielectrophoresis and high aspect ratio reaction-wells for confining the cell lysates extracted by lysing trapped single cells via electroporation. We demonstrated a highly efficient single-cell arraying (a cell capture efficiency of 96 ± 3%) by trapping diluted human prostate cancer cells (PC3 cells). On-chip single-cell analysis was performed by measuring the intracellular β-galactosidase (β-gal) activity after lysing the trapped single cells inside a tightly enclosed EdWA in the presence of a fluorogenic enzyme substrate. The PC3 cells showed large cell-to-cell variations in β-gal activity although they were cultured under the same conditions in a culture dish. This simple and effective system has great potential for high throughput single-cell analysis of rare cells.

Automated sample preparation in a microfluidic culture device for cellular metabolomics

Sample pretreatment in conventional cellular metabolomics entails rigorous lysis and extraction steps which increase the duration as well as limit the consistency of these experiments. We report a biomimetic cell culture microfluidic device (MFD) which is coupled with an automated system for rapid, reproducible cell lysis using a combination of electrical and chemical mechanisms. In-channel microelectrodes were created using facile fabrication methods, enabling the application of electric fields up to 1000 V cm(-1). Using this platform, average lysing times were 7.12 s and 3.03 s for chips with no electric fields and electric fields above 200 V cm(-1), respectively. Overall, the electroporation MFDs yielded a ∼10-fold improvement in lysing time over standard chemical approaches. Detection of multiple intracellular nucleotides and energy metabolites in MFD lysates was demonstrated using two different MS platforms. This work will allow for the integrated culture, automated lysis, and metabolic analysis of cells in an MFD which doubles as a biomimetic model of the vasculature.

Single cells in confined volumes: microchambers and microdroplets

Microfluidic devices capable of manipulating and guiding small fluid volumes open new methodical approaches in the fields of biology, pharmacy, and medicine. They have already proven their extraordinary value for cell analysis. The emergence of microfluidic platforms has paved the way to novel analytical strategies for the positioning, treatment and observation of living cells, for the creation of chemically defined liquid environments, and for tailoring biomechanical or physical conditions in small volumes. In this article, we particularly focus on two complementary approaches: (i) the isolation of cells in small chambers defined by microchannels and integrated valves and (ii) the encapsulation of cells in microdroplets. We review the advantages and limitations of both approaches and discuss their potential for single-cell analysis and related fields. Our intention is also to give a recommendation on which platform is most appropriate for a new question, i.e., a guideline to choose the most suitable platform.

Plasma nanotextured polymeric lab-on-a-chip for highly efficient bacteria capture and lysis

We describe the design, fabrication, and successful demonstration of a sample preparation module comprising bacteria cell capture and thermal lysis on-chip with potential applications in food sample pathogen analysis. Plasma nanotexturing of the polymeric substrate allows increase of the surface area of the chip and the antibody binding capacity. Three different anti-Salmonella antibodies were directly and covalently linked to plasma treated chips without any additional linker chemistry or other treatment. Then, the Ab-modified chips were tested for their capacity to bind bacteria in the concentration range of 10(2)-10(8) cells per mL; the module exhibited 100% efficiency in Salmonella enterica serovar Typhimurium bacteria capture for cell suspensions below 10(5) cells per mL (10(4) cells injected with a 100 μL sample volume) and efficiency higher than 50% for 10(7) cells per mL. Moreover, thermal lysis achieved on-chip from as low as 10 captured cells was demonstrated and shown to compare well with off-chip lysis. Excellent selectivity (over 1 : 300) was obtained in a sample containing, in addition to S. Typhimurium and E. coli bacteria.

Polymer Coatings in 3D-Printed Fluidic Device Channels for Improved Cellular Adherence Prior to Electrical Lysis

This paper describes the design and fabrication of a polyjet-based three-dimensional (3D)-printed fluidic device where poly(dimethylsiloxane) (PDMS) or polystyrene (PS) were used to coat the sides of a fluidic channel within the device to promote adhesion of an immobilized cell layer. The device was designed using computer-aided design software and converted into an .STL file prior to printing. The rigid, transparent material used in the printing process provides an optically transparent path to visualize endothelial cell adherence and supports integration of removable electrodes for electrical cell lysis in a specified portion of the channel (1 mm width × 0.8 mm height × 2 mm length). Through manipulation of channel geometry, a low-voltage power source (500 V max) was used to selectively lyse adhered endothelial cells in a tapered region of the channel. Cell viability was maintained on the device over a 5 day period (98% viable), though cell coverage decreased after day 4 with static media delivery. Optimal lysis potentials were obtained for the two fabricated device geometries, and selective cell clearance was achieved with cell lysis efficiencies of 94 and 96%. The bottleneck of unknown surface properties from proprietary resin use in fabricating 3D-printed materials is overcome through techniques to incorporate PDMS and PS.

Rapidly prototyped multi-scale electrodes to minimize the voltage requirements for bacterial cell lysis

Lab-on-a-chip systems used for nucleic acid based detection of bacteria rely on bacterial lysis for the release of cellular material. Although electrical lysis devices can be miniaturized for on-chip integration and reagent-free lysis, they often suffer from high voltage requirements, and rely on the use of off-chip voltage supplies. To overcome this barrier, we developed a rapid prototyping method for creating multi-scale electrodes that are structurally tuned for lowering the voltage needed for electrical bacterial lysis. These three-dimensional multi-scale electrodes – with micron scale reaction areas and nanoscale features – are fabricated using benchtop methods including craft cutting, polymer-induced wrinkling, and electrodeposition, which enable a lysis device to be designed, fabricated, and optimized in a matter of hours. These tunable electrodes show superior behaviour compared to lithographically-prepared electrodes in terms of lysis efficiency and voltage requirement. Successful extraction of nucleic acids from bacterial samples processed by these electrodes demonstrates the potential for these rapidly prototyped devices to be integrated within practical lab-on-a-chip systems.

Squaramide-based tripodal ionophores for potentiometric sulfate-selective sensors with high selectivity

A class of squaramide-based tripodal molecules was employed as new ionophores for highly sensitive and selective sulfate-selective sensors.

Donut-shaped chambers for analysis of biochemical processes at the cellular and subcellular levels

In order to study cell-cell variation with respect to enzymatic activity, individual live cell analysis should be complemented by measurement of single cell content in a biomimetic environment on a cellular scale arrangement. This is a challenging endeavor due to the small volume of a single cell, the low number of target molecules and cell motility. Micro-arrayed donut-shaped chambers (DSCs) of femtoliter (fL), picoliter (pL), and nanoliter (nL) volumes have been developed and produced for the analysis of biochemical reaction at the molecular, cellular and multicellular levels, respectively. DSCs are micro-arrayed, miniature vessels, in which each chamber acts as an individual isolated reaction compartment. Individual live cells can settle in the pL and nL DSCs, share the same space and be monitored under the microscope in a noninvasive, time-resolved manner. Following cell lysis and chamber sealing, invasive kinetic measurement based on cell content is achieved for the same individual cells. The fL chambers are used for the analysis of the same enzyme reaction at the molecular level. The various DSCs were used in this proof-of-principle work to analyze the reaction of intracellular esterase in both primary and cell line immune cell populations. These unique DSC arrays are easy to manufacture and offer an inexpensive and simple operating system for biochemical reaction measurement of numerous single cells used in various practical applications.

Recent advances in bioprinting and applications for biosensing

Future biosensing applications will require high performance, including real-time monitoring of physiological events, incorporation of biosensors into feedback-based devices, detection of toxins, and advanced diagnostics. Such functionality will necessitate biosensors with increased sensitivity, specificity, and throughput, as well as the ability to simultaneously detect multiple analytes. While these demands have yet to be fully realized, recent advances in biofabrication may allow sensors to achieve the high spatial sensitivity required, and bring us closer to achieving devices with these capabilities. To this end, we review recent advances in biofabrication techniques that may enable cutting-edge biosensors. In particular, we focus on bioprinting techniques (e.g., microcontact printing, inkjet printing, and laser direct-write) that may prove pivotal to biosensor fabrication and scaling. Recent biosensors have employed these fabrication techniques with success, and further development may enable higher performance, including multiplexing multiple analytes or cell types within a single biosensor. We also review recent advances in 3D bioprinting, and explore their potential to create biosensors with live cells encapsulated in 3D microenvironments. Such advances in biofabrication will expand biosensor utility and availability, with impact realized in many interdisciplinary fields, as well as in the clinic.

Hierarchical silicon nanospikes membrane for rapid and high-throughput mechanical cell lysis

This letter reports an efficient and compatible silicon membrane combining the physical properties of nanospikes and microchannel arrays for mechanical cell lysis. This hierarchical silicon nanospikes membrane was created to mechanically disrupt cells for a rapid process with high throughput, and it can be assembled with commercial syringe filter holders. The membrane was fabricated by photoelectrochemical overetching to form ultrasharp nanospikes in situ along the edges of the microchannel arrays. The intracellular protein and nucleic acid concentrations obtained using the proposed membrane within a short period of time were quantitatively higher than those obtained by routine, conventional acoustic and chemical lysis methods.

Reconfigurable microfluidics with integrated aptasensors for monitoring intercellular communication

We report the development of a microsystem integrating anti-TNF-α aptasensors with vacuum-actuatable microfluidic devices that may be used to monitor intercellular communications. Actuatable chambers were used to expose to mitogen a group of ~600 cells while not stimulating another group of monocytes only 600 μm away. Co-localizing groups of cells with miniature 300 μm diameter aptamer-modified electrodes enabled monitoring of TNF-α release from each group independently. The microsystem allowed observation of the sequence of events that included 1) mitogenic activation of the first group of monocytes to produce TNF-α, 2) diffusion of TNF-α to the location of the second group of cells and 3) activation of the second group of cells resulting in the production of TNF-α by these cells. Thus, we were able to experimentally verify reciprocal paracrine crosstalk between the two groups of cells secreting the same signalling molecule. Given the prevalence of such cellular communications during injury, cancer or immune response and the dearth of available monitoring techniques, the microsystem described here is envisioned to have significant impact on cell biology.

Toward integrated molecular diagnostic system (i MDx): principles and applications

Integrated molecular diagnostic systems ( iMDx), which are automated, sensitive, specific, user-friendly, robust, rapid, easy-to-use, and portable, can revolutionize future medicine. This review will first focus on the components of sample extraction, preservation, and filtration necessary for all point-of-care devices to include for practical use. Subsequently, we will look for low-powered and precise methods for both sample amplification and signal transduction, going in-depth to the details behind their principles. The final field of total device integration and its application to the clinical field will also be addressed to discuss the practicality for future patient care. We envision that microfluidic systems hold the potential to breakthrough the number of problems brought into the field of medical diagnosis today.

Emerging microfluidic devices for cell lysis: a review

Intracellular components containing information about genetic and disease characteristics are key substances to clinical diagnostics. Cell lysis is therefore a crucial step for efficient extraction and the subsequent analysis of intracellular components. With the advent of advanced manufacturing techniques, a number of micro systems have been proposed and applied for manipulating cells on chips. In this paper, we review emerging microfluidic devices for cell lysis. Different lysis mechanisms and related techniques are compared. The technical details, advantages, and limitations of various microfluidic devices are discussed.

Cell electroporation by CNT-featured microfluidic chip

We present the application of carbon nanotubes (CNTs) for cell electroporation that is performed in a microfluidic device. Lab on a chip (LOC) developments have raised unique possibilities to scale down cell manipulation systems to a cellular level to achieve higher performance and accuracy. Among the systems employed for cell disruption, electroporation without chemical reagents provides many advantages but suffers from high voltage requirements. We have exploited the electric field enhancement by CNTs to realize low-voltage electroporation. A microchip with embedded aligned CNTs has been developed to test the effect of the enhanced electric field on electroporation of mammalian CHO cells. Fluorogenic Calcein AM dye is used to image the release of the intercellular medium as an indication of electroporation. The electroporation phenomenon is recorded in real-time and compared with that of a device without CNTs. The results show that at a voltage as low as 3 volts, the electroporation yield rate is increased by 72% with the incorporation of CNTs. This enhancement is a promising advancement towards integration of low-voltage electroporation with other low-voltage cell manipulation techniques.

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.

Ultra-localized single cell electroporation using silicon nanowires

Analysis of cell-to-cell variation can further the understanding of intracellular processes and the role of individual cell function within a larger cell population. The ability to precisely lyse single cells can be used to release cellular components to resolve cellular heterogeneity that might be obscured when whole populations are examined. We report a method to position and lyse individual cells on silicon nanowire and nanoribbon biological field effect transistors. In this study, HT-29 cancer cells were positioned on top of transistors by manipulating magnetic beads using external magnetic fields. Ultra-rapid cell lysis was subsequently performed by applying 600-900 mV(pp) at 10 MHz for as little as 2 ms across the transistor channel and the bulk substrate. We show that the fringing electric field at the device surface disrupts the cell membrane, leading to lysis from irreversible electroporation. This methodology allows rapid and simple single cell lysis and analysis with potential applications in medical diagnostics, proteome analysis and developmental biology studies.

Analysis of intracellular reducing levels in human hepatocytes on three-dimensional focusing microchip

A novel three-dimensional hydrodynamic focusing microfluidic device integrated with high-throughput cell sampling and detection of intracellular contents is presented. It has a pivotal role in maintaining the reducing environment in cells. Intracellular reducing species such as vitamin C and glutathione in normal and tumor cells were labeled by a newly synthesized 2,2,6,6-tetramethyl-piperidine-1-oxyl-based fluorescent probe. Hepatocytes are adherent cells, which are prone to attaching to the channel surface. To avoid the attachment of cells on the channel surface, a single channel microchip with three sheath-flow channels located on both sides of and below the sampling channel was developed. Hydrostatic pressure generated by emptying the sample waste reservoir was used as driving force of fluid on the microchip. Owing to the difference between the liquid levels of the reservoirs, the labeled cells were three-dimensional hydrodynamically focused and transported from the sample reservoir to the sample waste reservoir. Hydrostatic pressure takes advantage of its ease of generation on a microfluidic chip without any external pressure pump, which drives three sheath-flow streams to constrain a sample flow stream into a narrow stream to avoid blockage of the sampling channel by adhered cells. The intracellular reducing levels of HepG2 cells and L02 cells were detected by home-built laser-induced fluorescence detector. The analysis throughput achieved in this microfluidic system was about 59-68 cells/min.

Microfluidic devices for high-throughput proteome analyses

Over the last decades, microfabricated bioanalytical platforms have gained enormous interest due to their potential to revolutionize biological analytics. Their popularity is based on several key properties, such as high flexibility of design, low sample consumption, rapid analysis time, and minimization of manual handling steps, which are of interest for proteomics analyses. An ideal totally integrated chip-based microfluidic device could allow rapid automated workflows starting from cell cultivation and ending with MS-based proteome analysis. By reducing or eliminating sample handling and transfer steps and increasing the throughput of analyses these workflows would dramatically improve the reliability, reproducibility, and throughput of proteomic investigations. While these complete devices do not exist for routine use yet, many improvements have been made in the translation of proteomic sample handling and separation steps into microfluidic formats. In this review, we will focus on recent developments and strategies to enable and integrate proteomic workflows into microfluidic devices.

Lab-on-a-chip: emerging analytical platforms for immune-mediated diseases

Miniaturization of analytical procedures has a significant impact on diagnostic testing since it provides several advantages such as: reduced sample and reagent consumption, shorter analysis time and less sample handling. Lab-on-a-chip (LoC), usually silicon, glass, or silicon-glass, or polymer disposable cartridges, which are produced using techniques inherited from the microelectronics industry, could perform and integrate the operations needed to carry out biochemical analysis through the mechanical realization of a dedicated instrument. Analytical devices based on miniaturized platforms like LoC may provide an important contribution to the diagnosis of high prevalence and rare diseases. In this paper we review some of the uses of Lab-on-a-chip in the clinical diagnostics of immune-mediated diseases and we provide an overview of how specific applications of these technologies could improve and simplify several complex diagnostic procedures.

Nanowire-integrated microfluidic devices for facile and reagent-free mechanical cell lysis

Cell lysis is an essential task for the detection of intracellular components. In this work, we introduce novel microfluidic devices integrated with patterned one-dimensional nanostructure arrays for facile and high-throughput mechanical cell lysis. The geometry of the hydrothermally grown ZnO nanowires, characterised by sharp tips and high aspect ratios, aids in anchoring the cell and tearing the plasma membrane, enabling simple and highly efficient extraction of cellular proteins and nucleic acids. This method lyses cells more effectively than conventional chemical lysis methods with simpler equipment and a shorter processing time.

Single-cell electric lysis on an electroosmotic-driven microfluidic chip with arrays of microwells

Accurate analysis at the single-cell level has become a highly attractive tool for investigating cellular content. An electroosmotic-driven microfluidic chip with arrays of 30-μm-diameter microwells was developed for single-cell electric lysis in the present study. The cellular occupancy in the microwells when the applied voltage was 5 V (82.4%) was slightly higher than that at an applied voltage of 10 V (81.8%). When the applied voltage was increased to 15 V, the cellular occupancy in the microwells dropped to 64.3%. More than 50% of the occupied microwells contain individual cells. The results of electric lysis experiments at the single-cell level indicate that the cells were gradually lysed as the DC voltage of 30 V was applied; the cell was fully lysed after 25 s. Single-cell electric lysis was demonstrated in the proposed microfluidic chip, which is suitable for high-throughput cell lysis.

Controlled electroporation of the plasma membrane in microfluidic devices for single cell analysis

Chemical cytometry on a single cell level is of interest to various biological fields ranging from cancer to stem cell research. The impact chemical cytometry can exert in these fields depends on the dimensionality of the retrievable analytes content. To this point, the number of different analytes identifiable and additionally their subcellular localization is of interest. To address this, we present an electroporation based approach for selective lysis of only the plasma membrane, which permits analysis of the dissolved cytoplasm, while reducing contributions from the nucleus and membrane bound fractions of the cell analytes. The use of 100 μs long pulse and a well defined DC electric field gradient of ∼4.5 kV·cm(-1) generated by 3D electrodes initiates release of a cytoplasm marker in ≪1 s, while retaining nuclear fluorescence markers.

Expanding the horizons for single-cell applications on lab-on-a-chip devices

Stochastic events in gene expression, protein synthesis, and metabolite synthesis or degradation lead to cellular heterogeneity essential to life. In a tissue as we see in organs, there is strong heterogeneity among the constituting cells critical to its function. Thus, there exists a strong demand to develop new micro/nanosystems that would enable us to conduct single-cell analysis. This field is rapidly growing, as exemplified below with recent emerging technologies that now reveal sensitive single-cell "omics" analysis. We describe in the review some of the most promising technologies that will certainly transform our view of biology in the near future.

Single-cell chemical lysis on microfluidic chips with arrays of microwells

Many conventional biochemical assays are performed using populations of cells to determine their quantitative biomolecular profiles. However, population averages do not reflect actual physiological processes in individual cells, which occur either on short time scales or nonsynchronously. Therefore, accurate analysis at the single-cell level has become a highly attractive tool for investigating cellular content. Microfluidic chips with arrays of microwells were developed for single-cell chemical lysis in the present study. The cellular occupancy in 30-μm-diameter microwells (91.45%) was higher than that in 20-μm-diameter microwells (83.19%) at an injection flow rate of 2.8 μL/min. However, most of the occupied 20-μm-diameter microwells contained individual cells. The results of chemical lysis experiments at the single-cell level indicate that cell membranes were gradually lysed as the lysis buffer was injected; they were fully lysed after 12 s. Single-cell chemical lysis was demonstrated in the proposed microfluidic chip, which is suitable for high-throughput cell lysis.

Electroactive microwell arrays for highly efficient single-cell trapping and analysis

We present a novel method, implemented in the form of a microfluidic device, for arraying and analyzing large populations of single cells. The device contains a large array of electroactive microwells where manipulation and analysis of large population of cells are carried out. On the device, single cells can be actively trapped in the microwells by dielectrophoresis (DEP) and then lysed by electroporation (EP) for subsequent analysis of the confined cell lysates. The DEP force in the selected dimensions of the microwells could achieve efficient trapping in nearly all the microwells (95%) in less than three minutes. Moreover, the positions of the cells in the microwells are maintained even when unstable flow of liquid is applied. This makes it possible to exchange the DEP buffer to a solution that will be subsequently used for stimulating or analyzing the trapped cells. After closing the microwells, EP is conducted to lyse the trapped cells by applying short electric pulses. Tight enclosure is critical to prevent dilution, diffusion and cross contamination of the cell lysates. We demonstrated the feasibility of our approach with an enzymatic assay measuring the intracellular-galactosidase activity. The use of this method should greatly help analysis of large populations of cells at the single-cell level. Furthermore, the method offers rapidity in the trapping and analysis of multiple cell types in physiological conditions that will be important to ensure the relevance of single cell analyses.

Advances in microfluidic PCR for point-of-care infectious disease diagnostics

Global burdens from existing or emerging infectious diseases emphasize the need for point-of-care (POC) diagnostics to enhance timely recognition and intervention. Molecular approaches based on PCR methods have made significant inroads by improving detection time and accuracy but are still largely hampered by resource-intensive processing in centralized laboratories, thereby precluding their routine bedside- or field-use. Microfluidic technologies have enabled miniaturization of PCR processes onto a chip device with potential benefits including speed, cost, portability, throughput, and automation. In this review, we provide an overview of recent advances in microfluidic PCR technologies and discuss practical issues and perspectives related to implementing them into infectious disease diagnostics.

High-throughput single-cell manipulation system for a large number of target cells

A sequential and high-throughput single-cell manipulation system for a large volume of cells was developed and the successive manipulation for single cell involving single-cell isolation, individual labeling, and individual rupture was realized in a microhydrodynamic flow channel fabricated by using two-dimensional simple flow channels. This microfluidic system consisted of the successive single-cell handlings of single-cell isolation from a large number of cells in cell suspension, labeling each isolated single cell and the lysate extraction from each labeled single cell. This microfluidic system was composed of main channels, cell-trapping pockets, drain channels, and single-cell content collection channels which were fabricated by polydimethylsiloxane. We demonstrated two kinds of prototypes for sequential single-cell manipulations, one was equipped with 16 single-cell isolation pockets in microchannel and the other was constructed of 512 single-cell isolation pockets. In this study, we demonstrated high-throughput and high-volume single-cell isolation with 512 pocket type device. The total number of isolated single cells in each isolation pocket from the cell suspension at a time was 426 for the cell line of African green monkey kidney, COS-1, and 360 for the rat primary brown preadipocytes, BAT. All isolated cells were stained with fluorescence dye injected into the same microchannel successfully. In addition, the extraction and collection of the cell contents was demonstrated using isolated stained COS-1 cells. The cell contents extracted from each captured cell were individually collected within each collection channel by local hydrodynamic flow. The sequential trapping, labeling, and content extraction with 512 pocket type devices realized high-throughput single-cell manipulations for innovative single-cell handling, feasible staining, and accurate cell rupture.

Continuous-flow electrical lysis device with integrated control by dielectrophoretic cell sorting

We present a device capable of electrical cell lysis and evaluation of lysis efficiency in continuous flow using dielectrophoretic cell sorting. We use a combination of AC electrical fields and so-called liquid electrodes to avoid bubble creation at the electrode surface. The electrical field distribution is calculated in different electrode configurations by numerical simulations. Cell sorting shows high lysis efficiency, 99% of yeast cells sorted after lysis featuring dielectric properties similar to dead cells. A study of the potential device throughput is performed.

Microfluidic Device for Capture and Isolation of Single Cells

We describe a microfluidic device capable of trapping, isolating, and lysing individual cells in parallel using dielectrophoretic forces and a system of PDMS channels and valves. The device consists of a glass substrate patterned with electrodes and two PDMS layers comprising of the microfluidic channels and valve control channels. Individual cells are captured by positive dielectrophoresis using the microfabricated electrode pairs. The cells are then isolated into nanoliter compartments using pneumatically actuated PDMS valves. Following isolation, the cells are lysed open by applying an electric field using the same electrode pairs. With the ability to capture and compartmentalize single cells our device may be combined with analytical methods for in situ molecular analysis of cellular components from single cells in a highly parallel manner.

The effects of flow type on aptamer capture in differential mobility cytometry cell separations

In this work, differential mobility cytometry (DMC) was used to monitor cell separation based on aptamer recognition for target cells. In this device, open-tubular capillaries coated with Sgc8 aptamers were used as affinity chromatography columns for separation. After cells were injected into the columns, oscillating flow was generated to allow for long-term cell adhesion studies. This process was monitored by optical microscopy, and differential imaging was used to analyze the cells as they adhered to the affinity surface. We investigated the capture time, capture efficiency, purity of target and control cells, as well as the reusability of the affinity columns. Capture time for both CCRF-CEM cells and Jurkat T cells was 0.4+/-0.2 s, which demonstrated the high separation affinity between aptamers and target cells. The capture efficiency for CCRF-CEM cells was 95% and purity was 99% in a cell mixture. With the advantage of both high cell capture efficiency and purity, DMC combined with aptamer-based separation emerges as a powerful tool for rare cell enrichment. In addition, aptamer-based DMC channels were found to be more robust than antibody based channels with respect to reuse of the separation device.

Single cell analytics: an overview

The research field of single cell analysis is rapidly expanding, driven by developments in flow cytometry, microscopy, lab-on-a-chip devices, and many other fields. The promises of these developments include deciphering cellular mechanisms and the quantification of cell-to-cell differences, ideally with spatio-temporal resolution. However, these promises are challenging as the analytical techniques have to cope with minute analyte amounts and concentrations. We formulate first these challenges and then present state-of-the-art analytical techniques available to investigate the different cellular hierarchies--from the genome to the phenome, i.e., the sum of all phenotypes.

Nucleic Acid-based Detection of Bacterial Pathogens Using Integrated Microfluidic Platform Systems

The advent of nucleic acid-based pathogen detection methods offers increased sensitivity and specificity over traditional microbiological techniques, driving the development of portable, integrated biosensors. The miniaturization and automation of integrated detection systems presents a significant advantage for rapid, portable field-based testing. In this review, we highlight current developments and directions in nucleic acid-based micro total analysis systems for the detection of bacterial pathogens. Recent progress in the miniaturization of microfluidic processing steps for cell capture, DNA extraction and purification, polymerase chain reaction, and product detection are detailed. Discussions include strategies and challenges for implementation of an integrated portable platform.