A microfluidic-based system for analysis of single cells based on Ca2+ flux

Cytosolic Calcium Measurement Utilizing a Single-Cell Biochip to Study the Effect of Curcumin and Resveratrol on a Single Glioma Cell

A microfluidic method has been developed for real-time measurement of the effects of curcumin on the intracellular calcium concentration in a single glioma cell (U87-MG). This method is based on quantitative fluorescence measurement of intracellular calcium in a cell selected in a single-cell biochip. This biochip consists of three reservoirs, three channels, and a V-shaped cell retention structure. Because of the adherent nature of glioma cells, a single cell can adhere within the aforementioned V-shaped structure. The single-cell calcium measurement will minimize cell damage caused by conventional cell calcium assay methods. Previous studies have shown that curcumin increased cytosolic calcium in glioma cells using the fluorescent dye: Fluo-4. So in this study, the effects of 5 μM and 10 μM solutions of curcumin on the increases of cytosolic calcium in a single glioma cell have been measured. Moreover, the effects of 100 μM and 200 μM of resveratrol are measured. At the final stage of the experiments, ionomycin was used to increase the intracellular calcium to the highest possible level due to dye saturation. It has been demonstrated that microfluidic cell calcium measurement is a real-time cytosolic assay that requires small quantities of reagent, which will have potential uses for drug discovery.

Technology advancement for integrative stem cell analyses

Scientists have endeavored to use stem cells for a variety of applications ranging from basic science research to translational medicine. Population-based characterization of such stem cells, while providing an important foundation to further development, often disregard the heterogeneity inherent among individual constituents within a given population. The population-based analysis and characterization of stem cells and the problems associated with such a blanket approach only underscore the need for the development of new analytical technology. In this article, we review current stem cell analytical technologies, along with the advantages and disadvantages of each, followed by applications of these technologies in the field of stem cells. Furthermore, while recent advances in micro/nano technology have led to a growth in the stem cell analytical field, underlying architectural concepts allow only for a vertical analytical approach, in which different desirable parameters are obtained from multiple individual experiments and there are many technical challenges that limit vertically integrated analytical tools. Therefore, we propose--by introducing a concept of vertical and horizontal approach--that there is the need of adequate methods to the integration of information, such that multiple descriptive parameters from a stem cell can be obtained from a single experiment.

Towards the miniaturization of GPCR-based live-cell screening assays

G protein-coupled receptors (GPCRs) play a key role in many physiological or disease-related processes and for this reason are favorite targets of the pharmaceutical industry. Although ~30% of marketed drugs target GPCRs, their potential remains largely untapped. The discovery of new leads calls for the screening of thousands of compounds with high-throughput cell-based assays. Although microtiter plate-based high-throughput screening platforms are well established, microarray and microfluidic technologies hold potential for miniaturization, automation, and biosensor integration that may well redefine the format of GPCR screening assays. This paper reviews the latest research efforts directed to bringing microarray and microfluidic technologies into the realm of GPCR-based, live-cell screening assays.

Strategies for the real-time detection of Ca2+ channel events of single cells: recent advances and new possibilities

Ca(2+) ion channels play key roles in cell physiology and they are important drug targets. The Ca(2+) channel events are mainly measurable by fluorescent and patch clamp methods. This review summarizes the recent advances of these techniques for the detection of Ca(2+) channel events and the prospect of their new directions in the near future. Conventional bulk fluorescent methods are amenable to high-throughput applications, but they are not real-time single-cell measurements, which provide kinetic data on individual cells and offer unparalleled sensitive data for rare cells. Recent advances on real-time single-cell fluorescent measurements are conducted on microfluidic chips with scalable cell-retention sites, integrated with electrical stimulation and fluorescent measuring features. Patch clamp techniques are real-time measurements conducted on single cells, but the measurements are of low throughput. Recent advances are conducted on microfluidic patch clamp chips for high-throughput applications. Future real-time single-cell Ca(2+) channel event measurements will be conducted in a multiparametric manner in an integrated and automated microfluidic chip.

Trapping cells on a stretchable microwell array for single-cell analysis

There is a need for a technology that can be incorporated into routine laboratory procedures to obtain a continuous, quantitative, fluorescence-based measurement of the dynamic behaviors of numerous individual living cells in parallel, while allowing other manipulations, such as staining, rinsing, and even retrieval of targeted cells. Here, we report a simple, low-cost microarray platform that can trap cells for dynamic single-cell analysis of mammalian cells. The elasticity of polydimethylsiloxane (PDMS) was utilized to trap tens of thousands of cells on an array. The PDMS microwell array was stretched by a tube through which cells were loaded on the array. Cells were trapped on the array by removal of the tube and relaxation of the PDMS. Once that was accomplished, the cells remained trapped on the array without continuous application of an external force and permitted subsequent manipulations, such as staining, rinsing, imaging, and even isolation of targeted cells. We demonstrate the utility of this platform by multicolor analysis of trapped cells and monitoring in individual cells real-time calcium flux after exposure to the calcium ionophore ionomycin. Additionally, a proof of concept for target cell isolation was demonstrated by using a microneedle to locally deform the PDMS membrane in order to retrieve a particular cell from the array.

A multishear microfluidic device for quantitative analysis of calcium dynamics in osteoblasts

Microfluidics is a convenient platform to study the influences of fluid shear stress on calcium dynamics. Fluidic shear stress has been proven to affect bone cell functions and remodelling. We have developed a microfluidic system which can generate four shear flows in one device as a means to study cytosolic calcium concentration ([Ca(2+)](c)) dynamics of osteoblasts. Four shear forces were achieved by having four cell culture chambers with different widths while resistance correction channels compensated for the overall resistance to allow equal flow distribution towards the chambers. Computational simulation of the local shear stress distribution highlighted the preferred section in the cell chamber to measure the calcium dynamics. Osteoblasts showed an [Ca(2+)](c) increment proportional to the intensity of the shear stress from 0.03 to 0.30 Pa. A delay in response was observed with an activation threshold between 0.03 and 0.06 Pa. With computational modelling, our microfluidic device can offer controllable multishear stresses and perform quantitative comparisons of shear stress-induced intensity change of calcium in osteoblasts.

Development of a microfluidic cell-based biosensor integrating a millisecond chemical pulse generator

The use of cell-based biosensors is usually limited by agonist-induced desensitization of cell-surface receptors. In this work, a microfluidic cell-based biosensor (μCBB) was developed for the detection of ATP in liquid environments. It consists of a millisecond chemical pulse generator for sample introduction in a pulsatile manner and a single NIH-3T3 cell expressing endogenous P2Y receptors as the sensing element. ATP solutions were used to simulate input signals for investigating the μCBB. By controlling negative pressures on two outlets of a cross-shaped microfluidic chip, pulses of ATP solutions were generated based on hydrodynamic gated injection. With ATP pulses of 100 ms every 50s, the amplitude of the resulting calcium spikes maintained at a similar level, suggesting that the receptor desensitization was minimized. Consequently, the developed μCBB could be used for detecting pulsatile samples with extended use times. The sensitivity of the μCBB for detecting ATP was further determined and the cellular responses to millisecond ATP pulses were investigated in comparison to long-term stimulations.

Microfluidic-based measurements of cytochrome P450 enzyme activity of primary mammalian hepatocytes

A microfluidic-based system was developed for the in situ monitoring of the 7-ethoxyresorufin O-dealkylation (EROD) activity of primary rat hepatocytes by measuring the fluorescent intensity of both cells and their surrounding media. The microfluidic chip was designed to allow the cell suspension and test reagent to be introduced in a layer-by-layer flow format, thereby resulting in a short mixing time by diffusion. A good linear relationship was obtained between the resorufin concentration up to 30 microM and fluorescent intensity over the chip's circular chamber area. The EROD activity was determined with 3-methylcholanthrene (3-MC)-induced hepatocytes. The inhibition effect of alpha-naphthoflavone was also examined on EROD activity resulting in an IC(50) value of 12.98 microM.

Translational nanomedicine: status assessment and opportunities

Nano-enabled technologies hold great promise for medicine and health. The rapid progress by the physical sciences/engineering communities in synthesizing nanostructures and characterizing their properties must be rapidly exploited in medicine and health toward reducing mortality rate, morbidity an illness imposes on a patient, disease prevalence, and general societal burden. A National Science Foundation-funded workshop, "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience," was held 16-19 March 2008 at the University of Southern California. Based on that workshop and literature review, this article briefly explores scientific, economic, and societal drivers for nanomedicine initiatives; examines the science, engineering, and medical research needs; succinctly reviews the US federal investment directly germane to medicine and health, with brief mention of the European Union (EU) effort; and presents recommendations to accelerate the translation of nano-enabled technologies from laboratory discovery into clinical practice.

FROM THE CLINICAL EDITOR

An excellent review paper based on the NSF funded workshop "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience" (16-19 March 2008) and extensive literature search, this paper briefly explores the current state and future perspectives of nanomedicine.

Real-time detection of the early event of cytotoxicity of herbal ingredients on single leukemia cells studied in a microfluidic biochip

A microfluidic approach has been developed for the real-time detection of drug effects, based on the quantitative measurement of calibrated cytosolic calcium ([Ca(2+)](i)) on single cancer cells. This microfluidic method is rapid by detecting the early event of cytotoxicity of drug candidates on cancer cells, without waiting for a couple of days needed for cell seeding and drug treatment by conventional assays. The miniaturized biochip consists of a V-shaped structure for the single-cell selection and retention. Various test reagents such as the chemotherapy drug (daunorubicin), an ionophore (ionomycin), and herbal ingredients from licorice (isoliquiritigenin or IQ) were investigated for their abilities to stimulate sustained cellular [Ca(2+)](i) elevations. The microfluidic results obtained in hours have been confirmed by conventional cytotoxicity assays which take days to complete. Moreover, any color or chemical interference problems found in the conventional assays of herbal compounds could be resolved. Using the microfluidic approach, IQ (50 microM) has been found to cause a sustained [Ca(2+)](i) elevation and cytotoxic effects on leukemia cells. The microfluidic single-cell analysis not only reduces reagent cost, and demands less cells, but also reveals some phenomena due to cellular heterogeneity that cannot be observed in bulk analysis.

Chemical cytometry on microfluidic chips

Chemical cytometry, referring to the analysis of the chemical contents in individual cells, has been in intensive study since Kennedy's first work that was published in Science. The early researches relied on fine-tip capillaries to capture the cells and do the analyses, which were lab- and time-intensive and required high skills of operation. The emergence of microfluidics has greatly spurred this research field and a great number of research papers have been published in the last decades. Highly integrated microfluidic chips have been developed to capture multiple single cells, lyse them, perform chemical reactions in enclosed microchambers, separate contents by CE and detect chemical species in individual cells. This review focuses on the development of relevant components and their integration for on-chip chemical cytometry.

Real-time monitoring of intracellular calcium dynamic mobilization of a single cardiomyocyte in a microfluidic chip pertaining to drug discovery

A microfluidic method for real-time quantitative measurement of cellular response pertaining to drug discovery is reported. This method is capable of multiple-step liquid delivery for measuring the drug response of a single cardiomyocyte, due to the improved cell retention by a newly designed chip. The chip, which consists of a cell-retention chamber with a weir structure, was fabricated just by a one-photomask microfabrication procedure followed by on-chip etching. This method differs from the conventional method, which uses two-mask photolithography to fabricate the microchannel (deep etch) and the weir structure (shallow etch). The dimensions of the weir structure have been predicted by a mathematical model, and confirmed by confocal microscopy. Using this microfluidic method, the dynamic [Ca2+]i mobilization in a single cardiomyocyte during its spontaneous contraction was quantified. Furthermore, we measured the cellular response of a cardiomyocyte on (i) a known cardiotonic agent (caffeine), (ii) a cardiotoxic chemotherapeutic drug (daunorubicin), and (iii) an herbal anticancer drug candidate - isoliquiritigenin (IQ) based on the fluorescent calcium measurement. It was found that IQ had produced a less pronounced effect on calcium mobilization( )of the cardiomyocytes whereas caffeine and daunorubicin had much stronger effects on the cells. These three experiments on cardiomyocytes pertaining to drug discovery were only possible after the improved cell retention provided by the new chip design (MV2) required for multiple-step real-time cellular analysis on a microchip, as compared with our old chip design (MV1).

Characterization of cellular chemical dynamics using combined microfluidic and Raman techniques

The integration of a range of technologies including microfluidics, surface-enhanced Raman scattering and confocal microspectroscopy has been successfully used to characterize in situ single living CHO (Chinese hamster ovary) cells with a high degree of spatial (in three dimensions) and temporal (1 s per spectrum) resolution. Following the introduction of a continuous flow of ionomycin, the real time spectral response from the cell was monitored during the agonist-evoked Ca²⁺ flux process. The methodology described has the potential to be used for the study of the cellular dynamics of a range of signalling processes.

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Optical filtering technologies for integrated fluorescence sensors

Numerous approaches have been taken to miniaturizing fluorescence sensing, which is a key capability for micro-total-analysis systems. This critical, comprehensive review focuses on the optical hardware required to attenuate excitation light while transmitting fluorescence. It summarizes, evaluates, and compares the various technologies, including filtering approaches such as interference filters and absorption filters and filterless approaches such as multicolor sensors and light-guiding elements. It presents the physical principles behind the different architectures, the state-of-the-art micro-fluorometers and how they were microfabricated, and their performance metrics. Promising technologies that have not yet been integrated are also described. This information will permit the identification of methods that meet particular design requirements, from both performance and integration perspectives, and the recognition of the remaining technological challenges. Finally, a set of performance metrics are proposed for evaluating and reporting spectral discrimination characteristics of integrated devices in order to promote side-by-side comparisons among diverse technologies and, ultimately, to facilitate optimized designs of micro-fluorometers for specific applications.

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.