Transport, location, and quantal release monitoring of single cells on a microfluidic device

Microfluidic platforms for single neuron analysis

Single-neuron actions are the basis of brain function, as clinical sequelae, neuronal dysfunction or failure for most of the central nervous system (CNS) diseases and injuries can be identified via tracing single-neurons. The bulk analysis methods tend to miscue critical information by assessing the population-averaged outcomes. However, its primary requisite in neuroscience to analyze single-neurons and to understand dynamic interplay of neurons and their environment. Microfluidic systems enable precise control over nano-to femto-liter volumes via adjusting device geometry, surface characteristics, and flow-dynamics, thus facilitating a well-defined micro-environment with spatio-temporal control for single-neuron analysis. The microfluidic platform not only offers a comprehensive landscape to study brain cell diversity at the level of transcriptome, genome, and/or epigenome of individual cells but also has a substantial role in deciphering complex dynamics of brain development and brain-related disorders. In this review, we highlight recent advances of microfluidic devices for single-neuron analysis, i.e., single-neuron trapping, single-neuron dynamics, single-neuron proteomics, single-neuron transcriptomics, drug delivery at the single-neuron level, single axon guidance, and single-neuron differentiation. Moreover, we also emphasize limitations and future challenges of single-neuron analysis by focusing on key performances of throughput and multiparametric activity analysis on microfluidic platforms.

A Review on Microfluidics: An Aid to Assisted Reproductive Technology

Infertility is a state of the male or female reproductive system that is defined as the failure to achieve pregnancy even after 12 or more months of regular unprotected sexual intercourse. Assisted reproductive technology (ART) plays a crucial role in addressing infertility. Various ART are now available for infertile couples. Fertilization in vitro (IVF), intracytoplasmic sperm injection (ICSI) and intrauterine insemination (IUI) are the most common techniques in this regard. Various microfluidic technologies can incorporate various ART procedures such as embryo and gamete (sperm and oocyte) analysis, sorting, manipulation, culture and monitoring. Hence, this review intends to summarize the current knowledge about the application of this approach towards cell biology to enhance ART.

Oncoimmunology Meets Organs-on-Chip

Oncoimmunology represents a biomedical research discipline coined to study the roles of immune system in cancer progression with the aim of discovering novel strategies to arm it against the malignancy. Infiltration of immune cells within the tumor microenvironment is an early event that results in the establishment of a dynamic cross-talk. Here, immune cells sense antigenic cues to mount a specific anti-tumor response while cancer cells emanate inhibitory signals to dampen it. Animals models have led to giant steps in this research context, and several tools to investigate the effect of immune infiltration in the tumor microenvironment are currently available. However, the use of animals represents a challenge due to ethical issues and long duration of experiments. Organs-on-chip are innovative tools not only to study how cells derived from different organs interact with each other, but also to investigate on the crosstalk between immune cells and different types of cancer cells. In this review, we describe the state-of-the-art of microfluidics and the impact of OOC in the field of oncoimmunology underlining the importance of this system in the advancements on the complexity of tumor microenvironment.

In situ probing of switchable nanomechanical properties of responsive high-density polymer brushes on poly(dimethylsiloxane): An AFM nanoindentation approach

Nanomechanical characteristics of end grafted polymer brushes were studied by AFM based, colloidal probe nanoindentation measurements. A high-density polymer brush of poly(2-hydroxyethyl methacrylate) (PHEMA) was precisely prepared on the surface of a flexible poly(dimethylsiloxane) (PDMS) substrate oxidized in ultraviolet/ozone (UVO). Exposure times less than 10min resulted in laterally homogeneous oxidized surfaces, characterized by a SiO_x thickness ∼35nm and an increased modulus up to 9MPa, as shown by AFM nanoindentation measurements. We have demonstrated that a high surface density of up to ∼0.63chains/nm² of the well-defined PHEMA brushes can be grown from the surface of oxidized PDMS by surface-initiated atom transfer radical polymerization (SI-ATRP) from trimethoxysilane derivatives mixed-SAM. The reversible nanomechanical changes of PHEMA layer between extended (hydrated state) and collapsed (dehydrated state) chain upon immersing in selective and non-selective solvents were investigated by in situ AFM nanoindentation analysis in liquid environments. The elastic modulus derived from force-indentation curves obtained for swollen PHEMA grafted chains in water was estimated to be equal 2.7±0.2MPa, which is almost two orders of magnitude smaller than the modulus of dry PHEMA brush. Additionally, under cyclohexane immersion, the modulus of the PHEMA layer decreased by one order of magnitude, indicating a more compact chain packing at the PDMS surface.

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.

Microfluidic Chip with Integrated Electrophoretic Immunoassay for Investigating Cell-Cell Interactions

Microfluidics have been used to create "body-on-chip" systems to mimic in vivo cellular interactions with a high level of control. Most such systems rely on optical observation of cells as a readout. In this work we integrated a cell-cell interaction chip with online microchip electrophoresis immunoassay to monitor the effects of the interaction on protein secretion dynamics. The system was used to investigate the effects of adipocytes on insulin secretion. Chips were loaded with 190 000 3T3-L1 adipocytes and a single islet of Langerhans in separate chambers. The chambers were perfused at 300-600 nL/min so that adipocyte secretions flowed over the islets for 3 h. Adipocytes produced 80 μM of nonesterified fatty acids (NEFAs), a factor known to impact insulin secretion, at the islets. After perfusion, islets were challenged with a step change in glucose from 3 to 11 mM while monitoring insulin secretion at 8 s intervals by online immunoassay. Adipocyte treatment augmented insulin secretion by 6-fold compared to controls. The effect was far greater than comparable concentrations of NEFA applied to the islets demonstrating that adipocytes release multiple factors that can strongly potentiate insulin secretion. The experiments reveal that integration of chemical analysis with cell-cell interaction can provide valuable insights into cellular functions.

Separation and Analysis of Adherent and Non-Adherent Cancer Cells Using a Single-Cell Microarray Chip

A new single-cell microarray chip was designed and developed to separate and analyze single adherent and non-adherent cancer cells. The single-cell microarray chip is made of polystyrene with over 60,000 microchambers of 10 different size patterns (31–40 µm upper diameter, 11–20 µm lower diameter). A drop of suspension of adherent carcinoma (NCI-H1650) and non-adherent leukocyte (CCRF-CEM) cells was placed onto the chip, and single-cell occupancy of NCI-H1650 and CCRF-CEM was determined to be 79% and 84%, respectively. This was achieved by controlling the chip design and surface treatment. Analysis of protein expression in single NCI-H1650 and CCRF-CEM cells was performed on the single-cell microarray chip by multi-antibody staining. Additionally, with this system, we retrieved positive single cells from the microchambers by a micromanipulator. Thus, this system demonstrates the potential for easy and accurate separation and analysis of various types of single cells.

Microfluidic Platform with In-Chip Electrophoresis Coupled to Mass Spectrometry for Monitoring Neurochemical Release from Nerve Cells

Chemical stimulus-induced neurotransmitter release from neuronal cells is well-documented. However, the dynamic changes in neurochemical release remain to be fully explored. In this work, a three-layered microfluidic chip was fabricated and evaluated for studying the dynamics of neurotransmitter release from PC-12 cells. The chip features integration of a nanoliter sized chamber for cell perfusion, pneumatic pressure valves for fluidic control, a microfluidic channel for electrophoretic separation, and a nanoelectrospray emitter for ionization in MS detection. Deploying this platform, a microchip electrophoresis-mass spectrometric method (MCE-MS) was developed to simultaneously quantify important neurotransmitters, including dopamine (DA), serotonin (5-HT), aspartic acid (Asp), and glutamic acid (Glu) without need for labeling or enrichment. Monitoring neurotransmitter release from PC-12 cells exposed to KCl (or alcohol) revealed that all four neurotransmitters investigated were released. Two release patterns were observed, one for the two monoamine neurotransmitters (i.e., DA and 5-HT) and another for the two amino acid neurotransmitters. Release dynamics for the two monoamine neurotransmitters was significantly different. The cells released DA most quickly and heavily in response to the stimulation. After exposure to the chemical stimulus for 4 min, the DA level in the perfusate from the cells was 86% lower than that at the beginning. Very interestingly, the cells started to release 5-HT in large quantities when they stopped releasing DA. These results suggest that DA and 5-HT are packaged into different vesicle pools and they are mobilized differently in response to chemical stimuli. The microfluidic platform proposed is proven useful for monitoring cellular release in biological studies.

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.

Digital Microfluidic Dynamic Culture of Mammalian Embryos on an Electrowetting on Dielectric (EWOD) Chip

Current human fertilization in vitro (IVF) bypasses the female oviduct and manually inseminates, fertilizes and cultivates embryos in a static microdrop containing appropriate chemical compounds. A microfluidic microchannel system for IVF is considered to provide an improved in-vivo-mimicking environment to enhance the development in a culture system for an embryo before implantation. We demonstrate a novel digitalized microfluidic device powered with electrowetting on a dielectric (EWOD) to culture an embryo in vitro in a single droplet in a microfluidic environment to mimic the environment in vivo for development of the embryo and to culture the embryos with good development and live births. Our results show that the dynamic culture powered with EWOD can manipulate a single droplet containing one mouse embryo and culture to the blastocyst stage. The rate of embryo cleavage to a hatching blastocyst with a dynamic culture is significantly greater than that with a traditional static culture (p<0.05). The EWOD chip enhances the culture of mouse embryos in a dynamic environment. To test the reproductive outcome of the embryos collected from an EWOD chip as a culture system, we transferred embryos to pseudo-pregnant female mice and produced live births. These results demonstrate that an EWOD-based microfluidic device is capable of culturing mammalian embryos in a microfluidic biological manner, presaging future clinical application.

New tools and new biology: recent miniaturized systems for molecular and cellular biology

Recent advances in applied physics and chemistry have led to the development of novel microfluidic systems. Microfluidic systems allow minute amounts of reagents to be processed using μm-scale channels and offer several advantages over conventional analytical devices for use in biological sciences: faster, more accurate and more reproducible analytical performance, reduced cell and reagent consumption, portability, and integration of functional components in a single chip. In this review, we introduce how microfluidics has been applied to biological sciences. We first present an overview of the fabrication of microfluidic systems and describe the distinct technologies available for biological research. We then present examples of microsystems used in biological sciences, focusing on applications in molecular and cellular biology.

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

A method was developed for the rapid separation of catecholamines by nonaqueous microchip electrophoresis (NAMCE) with LIF detection, A homemade pump-free negative pressure sampling device was used for rapid bias-free sampling in NAMCE, the injection time was 0.5 s and the electrophoresis separation conditions were optimized. Under the optimized conditions, the samples were separated completely in <1 min. The average migration times of the epinephrine (E), dopamine (DA), and norepinephrine (NE) were 34.26, 43.81, and 50.07 s, with an RSD of 1.05, 1.26, and 0.89% (n = 7), respectively. The linearity of the method ranged from 0.0125 to 2.0 mg/L for E and 0.025~4.0 mg/L for DA and NE, with correlation coefficients ranging between 0.9978 and 0.9986. The detection limits of E, DA, and NE were 2.5, 5.0, and 5.0 μg/L, respectively. The recoveries of E, DA, and NE in spiked urine samples were between 86 and 103%, with RSDs of 4.5~6.8% (n = 5). The proposed NAMCE with LIF detection combined with a pump-free negative pressure sampling device is a simple, inexpensive, energy efficient, miniaturized system that can be successfully applied for the determination of catecholamines in urine samples.

Recent advances in the development of single cell analysis--a review

Development of techniques for the analysis of the content of individual cells represents an important direction in modern bioanalytical chemistry. While the analysis of chromosomes, organelles, or location of selected proteins has been traditionally the domain of microscopic techniques, the advances in miniaturized analytical systems bring new possibilities for separations and detections of molecules inside the individual cells including smaller molecules such as hormones or metabolites. It should be stressed that the field of single cell analysis is very broad, covering advanced optical, electrochemical and mass spectrometry instrumentation, sensor technology and separation techniques. The number of papers published on single cell analysis has reached several hundred in recent years. Thus a complete literature coverage is beyond the limits of a journal article. The following text provides a critical overview of some of the latest developments with the main focus on mass spectrometry, microseparation methods, electrophoresis in capillaries and microfluidic devices and respective detection techniques for performing single cell analyses.

Isolation of motile spermatozoa with a microfluidic chip having a surface-modified microchannel

Conventional methods to prepare sperm have been amenable to the investigation of outcomes such as rates of recovery and conventional semen parameters. The standard preparation of sperm for assisted reproduction is criticized for its centrifugation steps, which might either recover motile sperm in variable proportions or increase the probability of damage to sperm DNA. An microfluidic system was designed to separate motile sperm according to a design whereby nonmotile spermatozoa and debris flow along their initial streamlines and exit through one outlet-up, whereas motile spermatozoa have an opportunity to swim into a parallel stream and to exit through a separate outlet-down. This chip was fabricated by microelectromechanical systems technology with polydimethylsiloxane molding. The hydrophilic surface, coated with poly (ethanediol) methyl ether methacrylate, exhibits enduring stability maintained for the microchannel. Microscopic examination and fluorescent images showed that the motility of sperm varied with the laminar streams. To confirm the sorting, we identified and quantified the proportions of live and dead sperm before and after sorting with flow cytometric analysis. The results on the viability of a sample demonstrated the increased quality of sperm after sorting and collection in the outlet reservoir. The counted ratio of live sperm revealed the quantity and efficiency of the sorted sperm.

Detection of single tumor cell resistance with aptamer biochip

In this study, a novel RNA aptamer biochip was developed for tumor cell capture and detection of single cell resistance. This biochip consists of a polydimethylsiloxane (PDMS) cover containing a channel for introducing cells and sustaining their activity and microelectrode matrix on a silicon dioxide layer. Epidermal growth factor receptor (EGFR) aptamers which specifically identify and isolate tumor cells were attached in the gap between two electrodes. After cell biochip incubation, surplus tumor cells were removed, and those dwelling on the intervals were further analyzed. When resistance measurement was completed, these cells were flushed away via controlled flow acceleration, and were collected for further analysis. The results demonstrate the convenience and efficiency of using anti-EGFR aptamer biochips for the detection of single cell resistance. This novel aptamer biochip may be used for the isolation of circulating tumor cells from peripheral blood and cell counting, or be assembled with other lab-on-a-chip components for follow-up gene and protein analysis.

Affinity and enzyme-based biosensors: recent advances and emerging applications in cell analysis and point-of-care testing

The applications of biosensors range from environmental testing and biowarfare agent detection to clinical testing and cell analysis. In recent years, biosensors have become increasingly prevalent in clinical testing and point-of-care testing. This is driven in part by the desire to decrease the cost of health care, to shift some of the analytical tests from centralized facilities to "frontline" physicians and nurses, and to obtain more precise information more quickly about the health status of a patient. This article gives an overview of recent advances in the field of biosensors, focusing on biosensors based on enzymes, aptamers, antibodies, and phages. In addition, this article attempts to describe efforts to apply these biosensors to clinical testing and cell analysis.

Dynamic monitoring of glucagon secretion from living cells on a microfluidic chip

A rapid microfluidic based capillary electrophoresis immunoassay (CEIA) was developed for on-line monitoring of glucagon secretion from pancreatic islets of Langerhans. In the device, a cell chamber containing living islets was perfused with buffers containing either high or low glucose concentration. Perfusate was continuously sampled by electroosmosis through a separate channel on the chip. The perfusate was mixed on-line with fluorescein isothiocyanate-labeled glucagon (FITC-glucagon) and monoclonal anti-glucagon antibody. To minimize sample dilution, the on-chip mixing ratio of sampled perfusate to reagents was maximized by allowing reagents to only be added by diffusion. Every 6 s, the reaction mixture was injected onto a 1.5-cm separation channel where free FITC-glucagon and the FITC-glucagon-antibody complex were separated under an electric field of 700 V cm(-1). The immunoassay had a detection limit of 1 nM. Groups of islets were quantitatively monitored for changes in glucagon secretion as the glucose concentration was decreased from 15 to 1 mM in the perfusate revealing a pulse of glucagon secretion during a step change. The highly automated system should be enable studies of the regulation of glucagon and its potential role in diabetes and obesity. The method also further demonstrates the potential of rapid CEIA on microfluidic systems for monitoring cellular function.

Microfluidic carbon-blackened polydimethylsiloxane device with reduced ultra violet background fluorescence for simultaneous two-color ultra violet/visible-laser induced fluorescence detection in single cell analysis

In single cell analysis (SCA), individual cell-specific properties and inhomogeneous cellular responses are being investigated that is not subjected to ensemble-averaging or heterogeneous cell population effects. For proteomic single cell analysis, ultra-sensitive and reproducible separation and detection techniques are essential. Microfluidic devices combined with UV laser induced fluorescence (UV-LIF) detection have been proposed to fulfill these requirements. Here, we report on a novel microfluidic chip fabrication procedure that combines straightforward production of polydimethylsiloxane (PDMS) chips with a reduced UV fluorescence background (83%-reduction) by using PDMS droplets with carbon black pigments (CBP) as additives. The CBP-droplet is placed at the point of detection, whereas the rest of the chip remains transparent, ensuring full optical control of the chip. We systematically studied the relation of the UV background fluorescence at CBP to PDMS ratios (varying from 1:10 to 1:1000) for different UV laser powers. Using a CBP/PDMS ratio of 1:20, detection of a 100 nM tryptophan solution (S/N = 3.5) was possible, providing a theoretical limit of detection of 86 nM (with S/N = 3). Via simultaneous two color UV/VIS-LIF detection, we were able to demonstrate the electrophoretic separation of an analyte mixture of 500 nM tryptophan (UV) and 5 nM fluorescein (VIS) within 30 s. As an application, two color LIF detection was also used for the electrophoretic separation of the protein content from a GFP-labeled single Spodoptera frugiperda (Sf9) insect cell. Thereby just one single peak could be measured in the visible spectral range that could be correlated with one single peak among others in the ultraviolet spectra. This indicates an identification of the labeled protein γ-PKC and envisions a further feasible identification of more than one single protein in the future.

Particles and microfluidics merged: perspectives of highly sensitive diagnostic detection

There is a growing need for diagnostic technologies that provide laboratories with solutions that improve quality, enhance laboratory system productivity, and provide accurate detection of a broad range of infectious diseases and cancers. Recent advances in micro- and nanoscience and engineering, in particular in the areas of particles and microfluidic technologies, have advanced the "lab-on-a-chip" concept towards the development of a new generation of point-of-care diagnostic devices that could significantly enhance test sensitivity and speed. In this review, we will discuss many of the recent advances in microfluidics and particle technologies with an eye towards merging these two technologies for application in medical diagnostics. Although the potential diagnostic applications are virtually unlimited, the most important applications are foreseen in the areas of biomarker research, cancer diagnosis, and detection of infectious microorganisms.

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.

Release monitoring of single cells on a microfluidic device coupled with fluorescence microscopy and electrochemistry

A method for monitoring the biological exocytotic phenomena on a microfluidic system was proposed. A microfluidic device coupled with functionalities of fluorescence imaging and amperometric detection has been developed to enable the real-time monitoring of the exocytotic events. Exocytotic release of single SH-SY5Y neuroblastoma cells was studied. By staining the cells located on integrated microelectrodes with naphthalene-2,3-dicarboxaldehyde, punctuate fluorescence consistent with localization of neurotransmitters stored in vesicles was obtained. The stimulated exocytotic release was successfully observed at the surface of SH-SY5Y cells without refitting the commercial inverted fluorescence microscope. Spatially and temporally resolved exocytotic events from single cells on a microfluidic device were visualized in real time using fluorescence microscopy and were amperometrically recorded by the electrochemical system simultaneously. This coupled technique is simple and is hoped to provide new insights into the mechanisms responsible for the kinetics of exocytosis.

Thermomodulated cell culture∕harvest in polydimethylsiloxane microchannels with poly(N-isopropylacrylamide)-grafted surface

Cell culture and harvest are the most upstream operation for a completely integrated cell assay chip. In our previous work, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was successfully grafted onto polydimethylsiloxane (PDMS) surface via benzophenone-initiated photopolymerization. In the present work, the PNIPAAm-grafted-PDMS (PNIPAAm-g-PDMS) surface was explored for thermomodulated cell culture and noninvasive harvest in microfluidic channels. Using COS 7 fibroblast from African green monkey kidney as the model cells, the thermomodulated adhering and detaching behaviors of the cells on the PNIPAAm-g-PDMS surfaces were optimized with respect to PNIPAAm-grafting yields and gelatin modification. The viability of the cells cultured on and harvested from the PNIPAAm-g-PDMS surface with the thermomodulated noninvasive protocol was estimated against the traditional cell culture∕harvest method involving trypsin digestion. The configuration of the microchannel on the PNIPAAm-g-PDMS chip was evaluated for static cell culture. Using a pipette-shaped PNIPAAm-g-PDMS microchannel, long-term cell culture could be achieved at 37 °C with periodic change of the culture medium every 12 h. After moving the microchip from the incubator set at 37 °C to the room temperature, the proliferated cells could be spontaneously detached from the PNIPAAm-g-PDMS surface of the upstream chamber and transferred by a gentle fluid flow to the downstream chamber, wherein the transferred cells could be subcultured. The thermomodulated cell culture, harvest, and passage operations on the PNIPAAm-g-PDMS microfluidic channels were demonstrated.

Measurements of movement and diffusion coefficients of single cells on polymeric surface from image analysis

Time-lapse digital images were taken every 30 s of PC12 cells cultured on polystyrene dishes, collagen-coated dishes and poly(L-lysine)-coated dishes in high-serum medium, low-serum medium and neurite outgrowth factor (NGF)-containing medium to investigate their diffusion coefficients (i.e., self-diffusion coefficients), D and specific movement (i.e., specific frequent movement) using image analysis and Fast Fourier Transform (FFT) analysis. D for these cells was found to fluctuate as a function of time, D varying between 0 and 0.08 microm(2)/s. The trend observed upon examination of average D values was: D in high-serum medium > or = D in low-serum medium > or = D in NGF-containing medium. Image analysis and FFT analysis of single cells cultured on polymeric dishes in these three media did not have any specific frequency of cell movement between 0 and 0.0167 Hz. The high diffusion coefficient and high amplitude of power spectra of PC12 cells in high-serum medium might be attributed to the high energy necessary for their continual suppression of the mitogen-activated protein kinase (MAPK) cascade and for them to maintain their undifferentiated state.

Real-time monitoring of oxidative burst from single plant protoplasts using microelectrochemical sensors modified by platinum nanoparticles

Oxidative bursts from plants play significant roles in plant disease defense and signal transduction; however, it has not hitherto been investigated on individual living plant cells. In this article, we fabricated a novel sensitive electrochemical sensor based on electrochemical deposition of Pt nanoparticles on the surface of carbon fiber microdisk electrodes via a nanopores containing polymer matrix, Nafion. The numerous hydrophilic nanochannels in the Nafion clusters coated on the electrode surface served as the molecular template for the deposition and dispersion of Pt, which resulted in the uniform construction of small Pt nanoparticles. The novel sensor displayed a high sensitivity for detection of H(2)O(2) with a detection limit of 5.0 x 10(-9) M. With the use of this microelectrochemical sensor, the oxidative burst from individual living plant protoplasts have been real-time monitored for the first time. The results showed that oxidative burst from single protoplasts triggered by a pathogen analogue were characterized by quanta release with a large number of "transient oxidative microburst" events, and protoplasts from the transgenic plants biologically displayed better disease-resistance and showed a distinguished elevation and longer-lasting oxidative burst.

Electrically evoking and electrochemically resolving quantal release on a microchip

A microchip was applied to electrically depolarize rat pheochromocytoma (PC12) cells and to simultaneously detect exocytotic catecholamine release amperometrically. Results demonstrate exocytosis elicited by flowing cells through an electric field generated by a potentiostat circuit in a microchannel, as well as exocytosis triggered by application of an extracellular voltage pulse across. Electrical finite element model (FEM) analysis illustrated that larger cells experienced greater depolarizing excitation from the extracellular electric fields due to the smaller shunt path and higher resistance to current flow in the channel around the cell. Consistent with these simulations, data recorded from cell clusters and large cells exhibited increased release rates relative to data from the smaller cells. Overall, the system was capable of resolving single vesicle quantal release, in the zeptomole range, as well as the kinetics associated with the vesicle fusion process. Analysis of spike population statistics suggested detection of catecholamines from multiple release sites around the cells. The potential for such a device to be used in flow cytometry to evoke and detect exocytosis was demonstrated.

Monitoring of vesicular exocytosis from single cells using micrometer and nanometer-sized electrochemical sensors

Communication between cells by release of specific chemical messengers via exocytosis plays crucial roles in biological process. Electrochemical detection based on ultramicroelectrodes (UMEs) has become one of the most powerful techniques in real-time monitoring of an extremely small number of released molecules during very short time scales, owing to its intrinsic advantages such as fast response, excellent sensitivity, and high spatiotemporal resolution. Great successes have been achieved in the use of UME methods to obtain quantitative and kinetic information about released chemical messengers and to reveal the molecular mechanism in vesicular exocytosis. In this paper, we review recent developments in monitoring exocytosis by use of UMEs-electrochemical-based techniques including electrochemical detection using micrometer and nanometer-sized sensors, scanning electrochemical microscopy (SECM), and UMEs implemented in lab-on-a-chip (LOC) microsystems. These advances are of great significance in obtaining a better understanding of vesicular exocytosis and chemical communications between cells, and will facilitate developments in many fields, including analytical chemistry, biological science, and medicine. Furthermore, future developments in electrochemical probing of exocytosis are also proposed.

In Vitro Electrochemistry of Biological Systems

This article reviews recent work involving electrochemical methods for in vitro analysis of biomolecules, with an emphasis on detection and manipulation at and of single cells and cultures of cells. The techniques discussed include constant potential amperometry, chronoamperometry, cellular electroporation, scanning electrochemical microscopy, and microfluidic platforms integrated with electrochemical detection. The principles of these methods are briefly described, followed in most cases with a short description of an analytical or biological application and its significance. The use of electrochemical methods to examine specific mechanistic issues in exocytosis is highlighted, as a great deal of recent work has been devoted to this application.

A micropillar-integrated smart microfluidic device for specific capture and sorting of cells

An integrated smart microfluidic device consisting of nickel micropillars, microvalves, and microchannels was developed for specific capture and sorting of cells. A regular hexagonal array of nickel micropillars was integrated on the bottom of a microchannel by standard photolithography, which can generate strong induced magnetic field gradients under an external magnetic field to efficiently trap superparamagnetic beads (SPMBs) in a flowing stream, forming a bed with sufficient magnetic beads as a capture zone. Fluids could be manipulated by programmed controlling the integrated air-pressure-actuated microvalves, based on which in situ bio-functionalization of SPMBs trapped in the capture zone was realized by covalent attachment of specific proteins directly to their surface on the integrated microfluidic device. In this case, only small volumes of protein solutions (62.5 nL in the capture zone; 375 nL in total volume needed to fill the device from inlet A to the intersection of outlet channels F and G) can meet the need for protein! The newly designed microfluidic device reduced greatly chemical and biological reagent consumption and simplified drastically tedious manual handling. Based on the specific interaction between wheat germ agglutinin (WGA) and N-acetylglucosamine on the cell membrane, A549 cancer cells were effectively captured and sorted on the microfluidic device. Capture efficiency ranged from 62 to 74%. The integrated microfluidic device provides a reliable technique for cell sorting.

Covalent modified hydrophilic polymer brushes onto poly(dimethylsiloxane) microchannel surface for electrophoresis separation of amino acids

A new environmentally friendly method is developed for preventing nonspecific biomolecules from adsorption on poly(dimethylsiloxane) (PDMS) surface via in situ covalent modification. o-[(N-Succinimdyl)succiny]-o'-methyl-poly(ethylene glycol) (NSS-mPEG) was covalently grafted onto PDMS microchannel surface that was pretreated by air-plasma and silanized with 3-aminopropyl-triethoxysilanes (APTES). The modification processes were carried out in aqueous solution without any organic solvent. The mPEG side chains displayed extended structure and created a nonionic hydrophilic polymer brushes layer on PDMS surface, which can effectively prevent the adsorption of biomolecules. The developed method had improved reproducibility of separation and stability of electroosmotic flow (EOF), enhanced hydrophilicity of surface and peak resolution, and decreased adsorption of biomolecules. EOF in the modified microchannel was strongly suppressed, compared with those in the native and silanized PDMS microchips. Seven amino acids have been efficiently separated and successfully detected on the coated PDMS microchip coupled with end-channel amperometric detection. Relative standard deviations (RSDs) of their migration time for run-to-run, day-to-day and chip-to-chip, were all below 2.3%. Moreover, the covalent-modified PDMS channels displayed long-term stability for 4 weeks. This novel coating strategy showed promising application in biomolecules separation.

Fully automated microchip system for the detection of quantal exocytosis from single and small ensembles of cells

A lab-on-a-chip device that enables positioning of single or small ensembles of cells on an aperture in close proximity to a mercaptopropionic acid (MPA) modified sensing electrode has been developed and characterized. The microchip was used for the detection of Ca(2+)-dependent quantal catecholamine exocytosis from single as well as small assemblies of rat pheochromocytoma (PC12) cells. The frequency of events increased considerably upon depolarization of the PC12 cell membrane using a high extracelluar concentration of potassium. The number of recorded events could be correlated with the number of cells immobilized on the electrode. Quantal characteristics, such as the number of released molecules per recorded event, are equivalent to data obtained using conventional carbon fiber microelectrodes. The detection sensitivity of the device allows for the detection of less than 10 000 dopamine molecules in a quantal release. The distribution of peak rise-time and full width at half maximum was constant during measurement periods of several minutes demonstrating the stability of the MPA modified surface.

A practical guide to microfluidic perfusion culture of adherent mammalian cells

Culturing cells at microscales allows control over microenvironmental cues, such as cell-cell and cell-matrix interactions; the potential to scale experiments; the use of small culture volumes; and the ability to integrate with microsystem technologies for on-chip experimentation. Microfluidic perfusion culture in particular allows controlled delivery and removal of soluble biochemical molecules in the extracellular microenvironment, and controlled application of mechanical forces exerted via fluid flow. There are many challenges to designing and operating a robust microfluidic perfusion culture system for routine culture of adherent mammalian cells. The current literature on microfluidic perfusion culture treats microfluidic design, device fabrication, cell culture, and micro-assays independently. Here we systematically present and discuss important design considerations in the context of the entire microfluidic perfusion culture system. These design considerations include the choice of materials, culture configurations, microfluidic network fabrication and micro-assays. We also present technical issues such as sterilization; seeding cells in both 2D and 3D configurations; and operating the system under optimized mass transport and shear stress conditions, free of air-bubbles. The integrative and systematic treatment of the microfluidic system design and fabrication, cell culture, and micro-assays provides novices with an effective starting point to build and operate a robust microfludic perfusion culture system for various applications.

Site-directed biotinylation of antibodies for controlled immobilization on solid surfaces

Site-directed biotinylation of antibodies at the hinge region was developed to immobilize antibodies in an oriented manner via biotin-streptavidin linkage. When intact antibody was biotinylated with maleimide-activated biotin after reduction, the reaction preferentially occurred at the sulfhydryl groups between the C(H1) and the C(L) domains and, provided that the reagent concentration exceeded a certain level, at those between the C(H2) and the C(H2) domains at the hinge. Based on this result, we devised an approach in which free maleimide was added to compete with the activated biotin for the preferential sites between the C(H1) and the C(L) domains. Since the smaller molecular size of free maleimide made it more accessible for the reaction than biotin, maleimide bound to the groups between the C(H1) and the C(L) domains first and thus conceded the groups between the C(H2) and the C(H2) domains to biotin under optimal conditions. In an alternative approach, selective biotinylation at the hinge was also achieved by reacting activated biotin with F(ab')(2) fragment prepared by enzymatic cleavage. This result indicated that, when free of Fc, the hinge structure, which contains the functional groups, of the fragment was open, allowing easy access to the biotin derivative from the aqueous medium. Both site-directed biotinylation preparations were tested as capture antibodies in sandwich-type immunoassays and compared to whole antibody randomly biotinylated at amino groups on the molecule. Preparations of both the intact antibody and the F(ab')(2) showed consistently enhanced detection capabilities that were 2.6 and 20 times that of the control, respectively.

Toward culture of single gametes: the development of microfluidic platforms for assisted reproduction

During the last few decades in vitro production of mammalian embryos and assisted reproductive technologies such as embryo transfer, cryopreservation, and cloning have been used to produce and propagate genetically superior livestock. However, efficiencies of these technologies remain low. For these technologies to become more commercially viable, the efficiencies must improve. Despite this importance of reproduction for the livestock industry, little progress in decreasing embryonic mortality has been made. The livestock industry has succeeded in achieving large increases in average milk production of dairy cattle, growth rate in beef cattle and leanness in swine but reproductive efficiency has actually decreased. For example, research has provided little progress toward developing an objective method to examine viability of a single living embryo. At the same time, the growth of miniaturization technologies beyond integrated circuits and toward small mechanical systems has created opportunities for fresh examination of a wide range of existing problems. While the investigation and application of miniaturization technologies to medicine and biology is progressing rapidly, there has been limited exploration of microfabricated systems in the area of embryo production. Microfluidics is an emerging technology that allows a fresh examination of the way assisted reproduction is performed. Here we review the progress in demonstrating microfluidic systems for in vitro embryo production (IVP) and embryo manipulation. Microfluidic technology could have a dramatic impact on the development of new techniques as well as on our basic understanding of gamete and embryo physiology.

In-situ grafting hydrophilic polymer on chitosan modified poly(dimethylsiloxane) microchip for separation of biomolecules

In this paper, a simple and green modification method is developed for biomolecules analysis on poly(dimethylsiloxane) (PDMS) microchip with successful depression of nonspecific biomolecules adsorption. O-[(N-succinimdyl)succiny]-o'-methyl-poly(ethylene glycol) was explored to form hydrophilic surface via in-situ grafting onto pre-coated chitosan (Chit) from aqueous solution in the PDMS microchannel. The polysaccharide chains backbone of Chit was strongly attracted onto the surface of PDMS via hydrophobic interaction combined with hydrogen bonding in an alkaline medium. The methyl-poly(ethylene glycol) (mPEG) could produce hydrophilic domains on the mPEG/aqueous interface, which generated brush-like coating in this way and revealed perfect resistance to nonspecific adsorption of biomolecules. This strategy could greatly improve separation efficiency and reproducibility of biomolecules. Amino acids and proteins could be efficiently separated and successfully detected on the coated microchip coupled with end-channel amperometric detection at a copper electrode. In addition, it offered an effective means for preparing biocompatible and hydrophilic surface on microfluidic devices, which may have potential use in the biological analysis.