Novel multi-depth microfluidic chip for single cell analysis

A novel multi-depth microfluidic chip was fabricated on glass substrate by use of conventional lithography and three-step etching technology. The sampling channel on the microchip was 37 microm deep, while the separation channel was 12 microm deep. A 1mm long weir was constructed in the separation channel, 300 microm down the channel crossing. The channel at the weir section was 6 microm deep. By using the multi-depth microfluidic chip, human carcinoma cells, which easily aggregate, settle and adhere to the surface of the channel, can be driven from the sample reservoir to the sample waste reservoir by hydrostatic pressure generated by the difference of liquid level between sample and sample waste reservoirs. Single cell loading into the separation channel was achieved by applying a set of pinching potentials at the four reservoirs. The loaded cell was stopped by the weir and precisely positioned within the separation channel. The trapped cell was lysed by sodium dodecyl sulfate (SDS) containing buffer solution in 20s. This approach reduced the lysing time and improved the reproducibility of chip-based electrophoresis separations. Reduced glutathione (GSH) and reactive oxygen species (ROS) were used as model intracellular components in single human carcinoma cells, and the constituents were separated by chip-based electrophoresis and detected by laser-induced fluorescence (LIF). A throughput of 15 samples/h, a migration time precision of 3.1% RSD for ROS and 4.9% RSD for GSH were obtained for 10 consecutively injected cells.     

A valve‐based microfluidic device for on‐chip single cell treatments

Assays toward single‐cell analysis have attracted the attention in biological and biomedical researches to reveal cellular mechanisms as well as heterogeneity. Yet nowadays microfluidic devices for single‐cell analysis have several drawbacks: some would cause cell damage due to the hydraulic forces directly acting on cells, while others could not implement biological assays since they could not immobilize cells while manipulating the reagents at the same time. In this work, we presented a two‐layer pneumatic valve‐based platform to implement cell immobilization and treatment on‐chip simultaneously, and cells after treatment could be collected non‐destructively for further analysis. Target cells could be encapsulated in sodium alginate droplets which solidified into hydrogel when reacted with Ca²⁺. The size of hydrogel beads could be precisely controlled by modulating flow rates of continuous/disperse phases. While regulating fluid resistance between the main channel and passages by the integrated pneumatic valves, on‐chip capture and release of hydrogel beads was implemented. As a proof of concept for on‐chip single‐cell treatments, we showed cellular live/dead staining based on our devices. This method would have potential in single cell manipulation for biochemical cellular assays.     

Laminar flow mediated continuous single-cell analysis on a novel poly(dimethylsiloxane) microfluidic chip

A novel microfluidic chip with simple design, easy fabrication and low cost, coupled with high-sensitive laser induced fluorescence detection, was developed to provide continuous single-cell analysis based on dynamic cell manipulation in flowing streams. Making use of laminar flows, which formed in microchannels, single cells were aligned and continuously introduced into the sample channel and then detection channel in the chip. In order to rapidly lyse the moving cells and completely transport cellular contents into the detection channel, the angle of the side-flow channels, the asymmetric design of the channels, and the number, shape and layout of micro-obstacles were optimized for effectively redistributing and mixing the laminar flows of single cells suspension, cell lysing reagent and detection buffer. The optimized microfluidic chip was an asymmetric structure of three microchannels, with three microcylinders at the proper positions in the intersections of channels. The microchip was evaluated by detection of anticancer drug doxorubicin (DOX) uptake and membrane surface P-glycoprotein (P-gp) expression in single leukemia K562 cells. An average throughput of 6–8 cells min⁻¹ was achieved. The detection results showed the cellular heterogeneity in DOX uptake and surface P-gp expression within K562 cells. Our researches demonstrated the feasibility and simplicity of the newly developed microfluidic chip for chemical single-cell analysis.     

Continuous analysis of dye-loaded, single cells on a microfluidic chip

Continuous analysis of two dyes loaded into single mammalian cells using laser-based lysis combined with electrophoretic separation was developed and characterized on microfluidic chips. The devices employed hydrodynamic flow to transport cells to a junction where they were mechanically lysed by a laser-generated cavitation bubble. An electric field then attracted the analyte into a separation channel while the membranous remnants passed through the intersection towards a waste reservoir. Phosphatidylcholine (PC)-supported bilayer membrane coatings (SBMs) provided a weakly negatively charged surface and prevented cell fouling from interfering with device performance. Cell lysis using a picosecond-pulsed laser on-chip did not interfere with concurrent electrophoretic separations. The effect of device parameters on performance was evaluated. A ratio of 2 : 1 was found to be optimal for the focusing-channel : flow-channel width and 3 : 1 for the flow-channel : separation-channel width. Migration times decreased with increased electric field strengths up to 333 V cm(-1), at which point the field strength was sufficient to move unlysed cells and cellular debris into the electrophoretic channel. The migration time and full width half-maximum (FWHM) of the peaks were independent of cell velocity for velocities between 0.03 and 0.3 mm s(-1). Separation performance was independent of the exact lysis location when lysis was performed near the outlet of the focusing channel. The migration time for cell-derived fluorescein and fluorescein carboxylate was reproducible with <10% RSD. Automated cell detection and lysis were required to reduce peak FWHM variability to 30% RSD. A maximum throughput of 30 cells min(-1) was achieved. Device stability was demonstrated by analyzing 600 single cells over a 2 h time span.     

A single cell electroporation chip

Increasing the cell membrane's permeability can be accomplished via single cell electroporation. Polar substances that cannot otherwise permeate the plasma membrane (such as dyes, drugs, DNA, proteins, peptides, and amino acids) can thus be introduced into the cell. We developed a polymeric chip that can selectively immobilize and locally electroporate single cells. This easy-to-use chip focuses the electric field, eliminating the need to manipulate electrodes or glass pipettes. Moreover, this device allows parallel single cell electroporation. We demonstrate the effectiveness of our device design by electroporating HeLa cells using low applied voltages (< 1 V). We found the average transmembrane potential required for electroporation of HeLa cells to be 0.51 +/- 0.13 V. Membrane permeation is assessed electrically by measuring characteristic 'jumps' in current that correspond to drops in cell resistance, and microscopically by recording either the escape of cytoplasmic dye Calcein AM or the entrance of Trypan blue stain.     

A microfluidic chip analyzer for determining neurotransmitters

The fabrication of a chip analyzer based on polydimethylsiloxane and glass has been described. The possibilities of the treatment of the chip channel surface by atmospheric plasma and sodium dodecyl sulphate used as an additive to the working buffer solution has been studied. The rate of electroosmotic flow was evaluated. Using a model mixture of catecholamines, the effect of modification of the surface of microchip channels on efficiency and separation factor was revealed. Methods for enhancing the sensitivity of the electrochemical cell have been developed; the possibilities of online preconcentration in the chip format were evaluated. The limit of detection for catecholamines has been attained at 10^?6–10^?7 g/mL.     

基于微流控芯片-质谱联用的细胞分析研究进展

微流控芯片与质谱联用为细胞研究提供了一个很好的研究平台.质谱的高灵敏度和对化合物独特的鉴别能力可以从复杂的化学信息背景中筛选识别出微量目标物,是细胞分析理想的检测手段.本文重点综述了近年来基于微流控芯片-质谱联用技术的细胞研究进展,从芯片-电喷雾质谱(ESI-MS)接口技术、集成化的样品前处理技术、细胞的药物代谢和细胞相互作用研究及基质辅助激光解吸电离质谱(MALDI-MS)的细胞分析应用等方面总结了最新的方法和技术发展.并展望了芯片-质谱联用新技术应用于细胞分析的可能性.     

A first step towards practical single cell proteomics: a microfluidic antibody capture chip with TIRF detection

We have developed a generic platform to undertake the analysis of protein copy number from single cells. The approach described here is 'all-optical' whereby single cells are manipulated into separate analysis chambers using an optical trap; single cells are lysed by a shock wave caused by laser-induced microcavitation, and the protein released from a single cell is measured by total internal reflection microscopy as it is bound to micro-printed antibody spots within the device. The platform was tested using GFP transfected cells and the relative precision of the measurement method was determined to be 88%. Single cell measurements were also made on a breast cancer cell line to measure the relative levels of unlabelled human tumour suppressor protein p53 using a chip incorporating an antibody sandwich assay format. These results suggest that this is a viable method for measuring relative protein levels in single cells.     

Modeling of misalignment effects in microfluidic interconnects for modular bio‐analytical chip applications

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip‐to‐chip or world‐to‐chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end‐to‐end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube‐in‐reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end‐to‐end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube‐in‐reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (L_e). Equivalent length calculations revealed that the effect of misalignment in tube‐in‐reservoir interconnection method was the least significant when compared to the other two methods of interconnection.     

A microfluidic array with cellular valving for single cell co-culture

We present a highly parallel microfluidic approach for contacting single cell pairs. The approach combines a differential fluidic resistance trapping method with a novel cellular valving principle for homotypic and heterotypic single cell co-culturing. Differential fluidic resistance was used for sequential single cell arraying, with the adhesion and flattening of viable cells within the microstructured environment acting to produce valves in the open state. Reversal of the flow was used for the sequential single cell arraying of the second cell type. Plasma stencilling, along the linear path of least resistance, was required to confine the cells within the trap regions. Prime flow conditions with minimal shear stress were identified for highly efficient cell arraying (～99%) and long term cell culture. Larger trap dimensions enabled the highest levels of cell pairing (～70%). The single cell co-cultures were in close proximity for the formation of connexon structures and the study of contact modes of communication. The research further highlights the possibility of using the natural behaviour of cells as the working principle behind responsive microfluidic elements.     

微流控芯片单细胞进样,溶膜及分离检测胞内谷胱甘肽

单细胞分析对重大疾病的早期诊断等方面有重要意义[1].微流控分析芯片的网络结构和微米级的通道尺寸适合于单细胞进样、溶膜和分离分析.但目前的报道主要集中在细胞培养、计数和筛选[2].我们在十字通道微流控芯片上,通过调节储液池的液面高度和细胞悬液密度,使单细胞逐个通过芯片进样通道和分离通道之间的区域,再结合控制电渗流方向,使单细胞固定在分离通指定位置,然后用电泳缓冲液结合高电场实现细胞快速溶膜,接着进行电泳分离和LIF检测.实现了单个血红细胞内谷胱甘肽(GSH)的高效分离及定量分析.     

A modular microfluidic system for deoxyribonucleic acid identification by short tandem repeat analysis

Microfluidic technology has been utilized in the development of a modular system for DNA identification through STR (short tandem repeat) analysis, reducing the total analysis time from the ∼6 h required with conventional approaches to less than 3 h. Results demonstrate the utilization of microfluidic devices for the purification, amplification, separation and detection of 9 loci associated with a commercially-available miniSTR amplification kit commonly used in the forensic community. First, DNA from buccal swabs purified in a microdevice was proven amplifiable for the 9 miniSTR loci via infrared (IR)-mediated PCR (polymerase chain reaction) on a microdevice. Microchip electrophoresis (ME) was then demonstrated as an effective method for the separation and detection of the chip-purified and chip-amplified DNA with results equivalent to those obtained using conventional separation methods on an ABI 310 Genetic Analyzer. The 3-chip system presented here demonstrates development of a modular, microfluidic system for STR analysis, allowing for user-discretion as to how to proceed after each process during the analysis of forensic casework samples.     

A scalable microfluidic chip for bacterial suspension culture

Microfluidic systems could, in principle, enable high-throughput breeding and screening of microbial strains for industrial applications, but parallel and scalable culture and detection chips are needed before complete microbial selection systems can be integrated and tested. Here we demonstrate a scalable multi-channel chip that is capable of bacterial suspension culture. The key invention is a multi-layered chip design, which enables a single set of control channels to function as serial peristaltic pumps to drive parallel culture chamber loops. Such design leads to scalability of the culture chip. We demonstrate that E. coli growth in the chip is equivalent or superior to conventional suspension culture on shaking beds. The chip could also be used for suspension culture of other microbes such as Bacillus subtilis, Pseudomonas stutzeri, and Zymomonas mobilis, indicating its general applicability for bacterial suspension culture.     

A cell electrofusion microfluidic chip using discrete coplanar vertical sidewall microelectrodes

A novel cell electrofusion microfluidic chip using discrete coplanar vertical sidewall electrodes has been designed, fabricated, and tested. The device contains a serpentine-shaped microchannel with 22 500 pairs of vertical sidewall microelectrodes patterned on two opposing vertical sidewalls of the microchannel. The adjacent microelectrodes on each sidewall are separated by coplanar SiO(2) -Polysilicon-SiO(2) /silicon. This design of coplanar discrete vertical sidewall electrodes eliminates the "dead area" present in previous designs using continuous three-dimensional (3D) protruding sidewall electrodes, and generates uniform electric field along the height of the microchannel, leading to a lower voltage required for cell fusion compared to designs using 2D thin-film electrodes. This device is tested to fuse NIH3T3 cells under a low voltage (～9 V). Almost 100% cells are aligned to the edge of the discrete microelectrodes, and cell-cell pairing efficiency reaches 70%. The electrofusion efficiency is above 40% of the total cells loaded into the device, which is much higher than traditional fusion methods and existing microfluidic devices using continuous 3D protruding sidewall microelectrodes.     

Characterization of cell lysis events on a microfluidic device for high-throughput single cell analysis

A microfluidic device capable of rapidly analyzing cells in a high-throughput manner using electrical cell lysis is further characterized. In the experiments performed, cell lysis events were studied using an electron multiplying charge coupled device camera with high frame rate (>100 fps) data collection. It was found that, with this microfluidic design, the path that a cell follows through the electric field affects the amount of lysate injected into the analysis channel. Elimination of variable flow paths through the electric field was achieved by coating the analysis channel with a polyamine compound to reverse the electroosmotic flow (EOF). EOF reversal forced the cells to take the same path through the electric field. The improved control of the cell trajectory will reduce device-imposed bias on the analysis and maximizes the amount of lysate injected into the analysis channel for each cell, resulting in improved analyte detection capabilities.     

Integrated microfluidic cell culture and lysis on a chip

We present an integrated microfluidic cell culture and lysis platform for automated cell analysis that improves on systems which require multiple reagents and manual procedures. Through the combination of previous technologies developed in our lab (namely, on-chip cell culture and electrochemical cell lysis) we have designed, fabricated, and characterized an integrated microfluidic platform capable of culturing HeLa, MCF-7, Jurkat, and CHO-K1 cells for up to five days and subsequently lysing the cells without the need to add lysing reagents. On-demand lysis was accomplished by local hydroxide ion generation within microfluidic chambers, releasing both proteinacious (GFP) and genetic (Hoescht-stained DNA) material. Sample proteins exposed to the electrochemical lysis conditions were immunodetectable (p53) and their enzymatic activity (HRP) was investigated.     

A new flow-type cell by the application of magnetic microfluidic chip

Using a magnetically formed channel called a magnetic channel, a new flow-type cell is proposed. The magnetic channel consists of magnetic walls that are formed by heterogeneous distributions of magnetic flux density around a ferromagnetic track under a magnetic field. The magnetic wall separates the paramagnetic oxidant solution from the diamagnetic reductant solution at a liquid–liquid interface without any solid membranes. In the magnetic channel formed on the cathode, the oxidant solution flows in a quasi-frictionless mode. The anode is placed in the reductant solution surrounding the magnetic channel. Such a geometrical configuration between the oxidant and reductant solutions is interchangeable depending on the magnetism of the solutions. To examine this concept, a Daniel cell system was adopted, where the copper ion in copper sulfate solution is employed as the oxidant and the zinc atom of zinc electrode as the reductant. The copper ion is paramagnetic, so that 1 mol dm⁻³ copper sulfate solution is injected into the magnetic channel formed on the copper cathode. Zinc sulfate solution (1 mol dm⁻³; diamagnetic) together with the zinc anode are placed surrounding the magnetic channel. The performance of this flow-type battery was examined up to a current density of 22 mA cm⁻². This paper was presented at the International Symposium on Magneto-Science 2005, Yokohama, 2005. Contribution to the special issue “Magnetic Field Effects in Electrochemistry.”     

Integration of single cell injection, cell lysis, separation and detection of intracellular constituents on a microfluidic chip

A microfluidic system was developed for the analysis of single biological cells, with functional integration of cell sampling, single cell loading, docking, lysing, and capillary electrophoretic (CE) separation with laser induced fluorescence (LIF) detection in microfabricated channels of a single glass chip. Channels were 12 microm deep and 48 microm wide, with a simple crossed-channel design. The effective separation channel length was 35 mm. During sampling with a cell suspension (cell population 1.2 x 10(5) cells per mL in physiological salt solution), differential hydrostatic pressure (created by adjusting liquid levels in the four reservoirs) was used to control cell flow exclusively through the channel crossing. Single cell loading into the separation channel was achieved by electrophoretic means by applying a set of potentials at the four reservoirs, counteracting the hydrostatic flow. A special docking (adhering) procedure for the loaded cell was applied before lysis by repeatedly connecting and disconnecting a set of low potentials, allowing precise positioning of the cell within the separation channel. Cell lysis was then effected within 40 ms under an applied CE separation voltage of 1.4 kV (280 V cm(-1)) within the working electrolyte (pH 9.2 borate buffer) without additional lysates. The docked lysing approach reduced dispersion of released intracellular constituents, and significantly improved the reproducibility of CE separations. Glutathione (GSH) was used as a model intracellular component in single human erythrocyte cells. NDA derivatized GSH was detected using LIF. A throughput of 15 samples h(-1), a retention time precision of 2.4% RSD was obtained for 14 consecutively injected cells. The average cellular concentration of GSH in human erythrocytes was found to be 7.2 [times] 10(-4)+/- 3.3 x 10(-4) M (63 +/- 29 amol per cell). The average separation efficiency for GSH in lysed cells was 2.13 x 10(6)+/- 0.4 x 10(6) plates per m, and was about a factor of 5 higher than those obtained with GSH standards using pinched injection.     

Performance of laser ablation: quadrupole-based ICP-MS coupling for the analysis of single micrometric uranium particles

In this paper we describe the application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) coupling to particle analysis, i.e., the determination of the isotopic composition of micrometric uranium particles. The performances of this analysis technique are compared with those of the two reference particle analysis techniques: secondary ion mass spectrometry (SIMS) and fission track-thermo-ionization mass spectrometry (FT-TIMS), based on the measurement of the isotopic ratios of ²³⁵U/²³⁸U in particles present in an inter-comparison particulate sample. The agreement of the results obtained using LA-ICP-MS with target values and with the results obtained using FT-TIMS and SIMS was good. Accuracy was equivalent to that of the other two techniques (±3 % deviation). However, relative experimental uncertainties present with LA-ICP-MS (7 %) were higher than those present with FT-TIMS (4.5 %) and SIMS (3 %). Furthermore, measurement yield of LA-ICP-MS coupling was close to that obtained with the same quadrupole ICP-MS for the measurement of a liquid sample (~10^?4), but lower than that obtained with FT-TIMS and SIMS, respectively, by a factor of 10 and 20, although the particles analyzed using LA-ICP-MS were most likely smaller (diameter ~0.6 μm, containing 4–7 fg of ²³⁵U). Nevertheless, thanks to the brevity of the signals obtained, the detection capacity for low isotopic concentrations by LA-ICP-MS coupling is equivalent to that of FT-TIMS, although it remains well below that of SIMS (×15). However, with more sensitive double focusing ICP-MS, performances equivalent to those achieved using SIMS could be obtained.