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1.
The capability of the AC dielectrophoresis (DEP) for on-chip capture and chaining of microalgae suspended in freshwaters was evaluated. The effects of freshwater composition as well as the electric field voltage, frequency, and duration, on the dielectrophoretic response of microalga Chlamydomonas reinhardtii were characterized systematically. Highest efficiency of cell alignment in one-dimensional arrays, determined by the percentage of cells in chain and the chain length, was obtained at AC-field of 20 V mm−1 and 1 kHz applied for 600 s. The DEP response and cell alignment of C. reinhardtii in water sampled from lake, pond, and river, as well as model media were affected by the chemical composition of the media. In the model media, the efficiency of DEP chaining was negatively correlated to the conductivity of the cell suspensions, being higher in suspensions with low conductivity. The cells suspended in freshwaters, however, showed anomalously high chaining at long exposure times. High concentrations of nitrate and dissolved organic matter decrease cell chaining efficiency, while phosphate and citrate concentrations increase it and favor formation of longer chains. Importantly, the application of AC-field had no effect on algal autofluorescence, cell membrane damage, or oxidative stress damages in C. reinhardtii. 相似文献
2.
We introduce a method for improved dielectrophoretic (DEP) discrimination and separation of viable and nonviable yeast cells. Due to the higher cell wall permeability of nonviable yeast cells compared with their viable counterpart, the cross-linking agent glutaraldehyde (GLT) is shown to selectively cross-link nonviable cells to a much greater extent than viable yeast. The DEP crossover frequency (cof) of both viable and nonviable yeast cells was measured over a large range of buffer conductivities (22 μS∕cm–400 μS∕cm) in order to study this effect. The results indicate that due to selective nonviable cell cross-linking, GLT modifies the DEP cof of nonviable cells, while viable cell cof remains relatively unaffected. To investigate this in more detail, a dual-shelled oblate spheroid model was evoked and fitted to the cof data to study cell electrical properties. GLT treatment is shown to minimize ion leakage out of the nonviable yeast cells by minimizing changes in cytoplasm conductivity over a large range of ionic concentrations. This effect is only observable in nonviable cells where GLT treatment serves to stabilize the cell cytoplasm conductivity over a large range of buffer conductivity and allow for much greater differences between viable and nonviable cell cofs. As such, by taking advantage of differences in cell wall permeability GLT magnifies the effect DEP has on the field induced separation of viable and nonviable yeasts. 相似文献
3.
Marija Nikolic-Jaric Tim Cabel Elham Salimi Ashlesha Bhide Katrin Braasch Michael Butler Greg E. Bridges Douglas J. Thomson 《Biomicrofluidics》2013,7(2)
The instrument described here is an all-electronic dielectrophoresis (DEP) cytometer sensitive to changes in polarizability of single cells. The important novel feature of this work is the differential electrode array that allows independent detection and actuation of single cells within a short section ( ～ 300?μm) of the microfluidic channel. DEP actuation modifies the altitude of the cells flowing between two altitude detection sites in proportion to cell polarizability; changes in altitude smaller than 0.25 μm can be detected electronically. Analysis of individual experimental signatures allows us to make a simple connection between the Clausius-Mossotti factor (CMF) and the amount of vertical cell deflection during actuation. This results in an all-electronic, label-free differential detector that monitors changes in physiological properties of the living cells and can be fully automated and miniaturized in order to be used in various online and offline probes and point-of-care medical applications. High sensitivity of the DEP cytometer facilitates observations of delicate changes in cell polarization that occur at the onset of apoptosis. We illustrate the application of this concept on a population of Chinese hamster ovary (CHO) cells that were followed in their rapid transition from a healthy viable to an early apoptotic state. DEP cytometer viability estimates closely match an Annexin V assay (an early apoptosis marker) on the same population of cells. 相似文献
4.
Ronald Pethig 《Biomicrofluidics》2010,4(2)
This Special Topic section is on dielectrophoresis, a growing area of widespread interest and relevance to the microfluidics and nanofluidics community.There was a time when the arrival of a telegram from the local post office would foreshadow a step-function change in one’s equilibrium. An internet service provider can now deliver the same effect, as illustrated by an unexpected e-mail from Leslie Yeo inquiring if I would “be interested in guest editing a special issue of Biomicrofluidics on recent advances in dielectrophoresis (DEP).” Flattery directed towards vanity can produce interesting results—which I hope this special issue of Biomicrofluidics demonstrates. The rationale for this special issue is the belief of the journal’s Editors (Dr. Chia Chang and Dr. Leslie Yeo) that dielectrophoresis is a growing area of widespread interest and relevance to the microfluidics and nanofluidics community. Papers, both fundamental and applied, were solicited from the leaders working across this broad interdisciplinary area of research. I was delighted by the positive responses of those whose invited contributions appear in this special issue—efforts certainly not motivated by vanity but through enthusiasm for the subject. Some of those invited to contribute were unable to do so because of other demands on their time. Ongoing advances being made in DEP, especially in its various applications, will surely merit another special issue in the future and hopefully include contributions from those unable to do so now.Two of the papers in this special issue address fundamental aspects of dielectrophoresis (DEP), namely the influences on DEP from electrical double-layers and from particle-particle interactions. Consideration of electrical double layers associated with charged particle surfaces is particularly important for nanoparticles because their effective polarizabilities, associated with field-induced dynamics of the counterions and co-ions in the double layer, can dominate over the intrinsic polarizability of the particle itself. This can influence, for example, to what extent the observation of changes in the DEP crossover frequency (marking the transition between positive and negative DEP) can be relied upon in new immunoassays based on the DEP behavior of functionalized nanoparticles. By considering the electrodynamics of double layers, Basuray et al.1 propose a theory to predict how the DEP crossover frequency will vary as a function of particle size and the ionic strength of the suspending electrolyte. In their paper, Sancho et al.2 derive a theoretical model to describe how particle-particle interactions (e.g., “pearl-chaining”) influence the DEP crossover frequency value. This model also describes well the changes in electrorotation and a newly observed precession effect as particles approach each other under the influence of a rotating field.DEP at the nanoscale is also addressed in contributions from the groups of Ralph Hölzel, Junya Suehiro, and Karan Kaler. Thus, Henning et al.3 describe a new method, based on the measurement of capacitance changes between planar microelectrodes, for the automatic acquisition of the DEP properties of nanoparticles without the need for labeling protocols or visual observations. Suehiro4 describes how DEP can be employed as a bottom-up approach for fabricating nanomaterial-based devices such as a carbon nanotube gas sensor and a ZnO nanowire photosensor. Kaler et al.5 describe how the DEP manipulation of miniscule amounts of polar aqueous samples, a method known as liquid-DEP, can be used for on-chip bioassays, such as nucleic acid analysis, and through parallel sample processing offer the potential for conducting automated multiplexed assays. The use of DEP to selectively trap and separate cells has been investigated over many years, and contributions from the groups of Hywel Morgan, Ana Valero, Masau Washizu, and Gerard Markx describe the latest advances and applications. Thomas et al.6 describe a new automated DEP cell trap design for the isolation, concentration, separation, and recovery of human osteoblast-like cells from a heterogeneous population. Recovery of small populations of human osteoblast-like cells with a purity of 100% is demonstrated. A cell-sorting device, based on the opposition of DEP forces that discriminates between cell types according to such properties as their membrane permittivity and cytoplasm conductivity, is described by Valeroet al.7 The versatility of the device is demonstrated by synchronizing a yeast cell culture at a particular phase of the cell cycle. Gel et al.8 describe a DEP-assisted cell trapping method for fusing pairs of cells in an array of micro-orifices. This method produces not only a high yield of viable cell fusants, but also allows for subsequent study of postfusion cell development. Zhu et al.9 describe a DEP-based microfluidic separation system in which dead and active cells can be collected from a given cell suspension, whilst at the same time eluting dormant cells. In the second paper from Gerard Markx’s group, Zhu et al.10 demonstrate that the rate-limiting resuscitation of a colony of dormant bacteria is determined by the diffusion of a resuscitation-promoting factor into the colony interior. This study involved the artificial engineering of different sizes and shapes of bacterial aggregates using DEP forces. Finally, in my own contribution,11 I have attempted to summarize the growing output of DEP publications in terms of their contributions to the theory, technology, and applications of DEP. 相似文献
5.
A microfluidic device with planar square electrodes is developed for capturing particles from high conductivity media using negative dielectrophoresis (n-DEP). Specifically, Bacillus subtilis and Clostridium sporogenes spores, and polystyrene particles are tested in NaCl solution (0.05 and 0.225 S∕m), apple juice (0.225 S∕m), and milk (0.525 S∕m). Depending on the conductivity of the medium, the Joule heating produces electrothermal flow (ETF), which continuously circulates and transports the particles to the DEP capture sites. Combination of the ETF and n-DEP results in different particle capture efficiencies as a function of the conductivity. Utilizing 20 μm height DEP chambers, “almost complete” and rapid particle capture from lower conductivity (0.05 S∕m) medium is observed. Using DEP chambers above 150 μm in height, the onset of a global fluid motion for high conductivity media is observed. This motion enhances particle capture on the electrodes at the center of the DEP chamber. The n-DEP electrodes are designed to have well defined electric field minima, enabling sample concentration at 1000 distinct locations within the chip. The electrode design also facilitates integration of immunoassay and other surface sensors onto the particle capture sites for rapid detection of target micro-organisms in the future. 相似文献
6.
Mohammed Alshareef Nicholas Metrakos Eva Juarez Perez Fadi Azer Fang Yang Xiaoming Yang Guiren Wang 《Biomicrofluidics》2013,7(1)
The present work demonstrates the use of a dielectrophoretic lab-on-a-chip device in effectively separating different cancer cells of epithelial origin for application in circulating tumor cell (CTC) identification. This study uses dielectrophoresis (DEP) to distinguish and separate MCF-7 human breast cancer cells from HCT-116 colorectal cancer cells. The DEP responses for each cell type were measured against AC electrical frequency changes in solutions of varying conductivities. Increasing the conductivity of the suspension directly correlated with an increasing frequency value for the first cross-over (no DEP force) point in the DEP spectra. Differences in the cross-over frequency for each cell type were leveraged to determine a frequency at which the two types of cell could be separated through DEP forces. Under a particular medium conductivity, different types of cells could have different DEP behaviors in a very narrow AC frequency band, demonstrating a high specificity of DEP. Using a microfluidic DEP sorter with optically transparent electrodes, MCF-7 and HCT-116 cells were successfully separated from each other under a 3.2 MHz frequency in a 0.1X PBS solution. Further experiments were conducted to characterize the separation efficiency (enrichment factor) by changing experimental parameters (AC frequency, voltage, and flow rate). This work has shown the high specificity of the described DEP cell sorter for distinguishing cells with similar characteristics for potential diagnostic applications through CTC enrichment. 相似文献
7.
BackgroundChinese hamster ovary (CHO) cells are the most dependable mammalian cells for the production of recombinant proteins. Replication-incompetent retroviral vector (retrovector) is an efficient tool to generate stable cell lines. Multiple copies of integrated genes by retrovector transduction results in improved recombinant protein yield. HEK-293 and their genetic derivatives are principal cells for retrovector production. Retrovectors packaged in HEK-293 cells pose a risk of infectious agent transmission, such as viruses and mycoplasmas, from serum and packaging cells.ResultsIn this report, retrovectors were packaged in CHO cells cultured in chemically defined (CD) media. The retrovectors were then used to transduce CHO cells. This method can block potential transmission of infectious agents from serum and packaging cells. With this method, we generated glucagon-like protein-1 Fc fusion protein (GLP-1-Fc) stable expression CHO cell lines. Productivity of GLP-1-Fc can reach 3.15 g/L. The GLP-1-Fc protein produced by this method has comparable bioactivity to that of dulaglutide (Trulicity). These stable cell lines retain 95–100% of productivity after 40 days of continuous culture (~ 48–56 generations).ConclusionsSuspension CHO cells are clean, safe, and reliable cells for retrovector packaging. Retrovectors packaged from this system could be used to generate CHO stable cell lines for recombinant protein expression.How to cite: Li J, Wei S, Cao C, et al. Retrovectors packaged in CHO cells to generate GLP-1-Fc stable expression CHO cell lines. Electron J Biotechnol 2019;41. https://doi.org/10.1016/j.ejbt.2019.07.002. 相似文献
8.
Characterization and separation of Cryptosporidium and Giardia cells using on-chip dielectrophoresis
Narayanan Unni H Hartono D Yue Lanry Yung L Mah-Lee Ng M Pueh Lee H Cheong Khoo B Lim KM 《Biomicrofluidics》2012,6(1):12805-1280514
Dielectrophoresis (DEP) has been shown to have significant potential for the characterization of cells and could become an efficient tool for rapid identification and assessment of microorganisms. The present work is focused on the trapping, characterization, and separation of two species of Cryptosporidium (C. parvum and C. muris) and Giardia lambia (G. lambia) using a microfluidic experimental setup. Cryptosporidium oocysts, which are 2-4 μm in size and nearly spherical in shape, are used for the preliminary stage of prototype development and testing. G. lambia cysts are 8–12 μm in size. In order to facilitate effective trapping, simulations were performed to study the effects of buffer conductivity and applied voltage on the flow and cell transport inside the DEP chip. Microscopic experiments were performed using the fabricated device and the real part of Clausius—Mossotti factor of the cells was estimated from critical voltages for particle trapping at the electrodes under steady fluid flow. The dielectric properties of the cell compartments (cytoplasm and membrane) were calculated based on a single shell model of the cells. The separation of C. muris and G. lambia is achieved successfully at a frequency of 10 MHz and a voltage of 3 Vpp (peak to peak voltage). 相似文献
9.
A modified theory is proposed for extracting cell dielectric properties from the peak frequency measurement of electrorotation (ER) and the crossover frequency measurement of dielectrophoresis (DEP). Current theory in the literature is based on the low frequency (DC) approximations for the equivalent cell permittivity and conductivity, which are valid when the measurements are performed in a medium with conductivity less than 1 mS/m. The present theory extracts the cell properties through optimizing an expression for the medium conductivity in terms of the peak ER, or DEP crossover, frequency according to its definition using full expressions of equivalent cell permittivity and conductivity. Various levels of approximation of the theory are proposed and discussed through a scaling analysis. The present theory can extract both membrane and interior properties from the low and the high peak ER, or DEP crossover, frequencies for any medium conductivity provided the peak ER, or DEP crossover, frequency exists. It can be reduced to the linear theory for the low peak ER and DEP crossover frequencies in the literature when the medium conductivity is less than 10 mS/m. However, we can determine the membrane capacitance and conductance via the slope and intercept, respectively, of the straight line fitting of the ER peak and DEP frequency against medium conductivity data according to the linear theory only when the intercept dominates the experimental uncertainty, which occurs when the medium conductivity is less than 1 mS/m in practice. 相似文献
10.
Massimo Muratore Vlastimil Srsen Martin Waterfall Andrew Downes Ronald Pethig 《Biomicrofluidics》2012,6(3)
Myoblasts are muscle derived mesenchymal stem cell progenitors that have great potential for use in regenerative medicine, especially for cardiomyogenesis grafts and intracardiac cell transplantation. To utilise such cells for pre-clinical and clinical applications, and especially for personalized medicine, it is essential to generate a synchronised, homogenous, population of cells that display phenotypic and genotypic homogeneity within a population of cells. We demonstrate that the biomarker-free technique of dielectrophoresis (DEP) can be used to discriminate cells between stages of differentiation in the C2C12 myoblast multipotent mouse model. Terminally differentiated myotubes were separated from C2C12 myoblasts to better than 96% purity, a result validated by flow cytometry and Western blotting. To determine the extent to which cell membrane capacitance, rather than cell size, determined the DEP response of a cell, C2C12 myoblasts were co-cultured with GFP-expressing MRC-5 fibroblasts of comparable size distributions (mean diameter ∼10 μm). A DEP sorting efficiency greater than 98% was achieved for these two cell types, a result concluded to arise from the fibroblasts possessing a larger membrane capacitance than the myoblasts. It is currently assumed that differences in membrane capacitance primarily reflect differences in the extent of folding or surface features of the membrane. However, our finding by Raman spectroscopy that the fibroblast membranes contained a smaller proportion of saturated lipids than those of the myoblasts suggests that the membrane chemistry should also be taken into account. 相似文献
11.
Sangjo Shim Katherine Stemke-Hale Apostolia M. Tsimberidou Jamileh Noshari Thomas E. Anderson Peter R. C. Gascoyne 《Biomicrofluidics》2013,7(1)
Circulating tumor cells (CTCs) are prognostic markers for the recurrence of cancer and may carry molecular information relevant to cancer diagnosis. Dielectrophoresis (DEP) has been proposed as a molecular marker-independent approach for isolating CTCs from blood and has been shown to be broadly applicable to different types of cancers. However, existing batch-mode microfluidic DEP methods have been unable to process 10 ml clinical blood specimens rapidly enough. To achieve the required processing rates of 106 nucleated cells/min, we describe a continuous flow microfluidic processing chamber into which the peripheral blood mononuclear cell fraction of a clinical specimen is slowly injected, deionized by diffusion, and then subjected to a balance of DEP, sedimentation and hydrodynamic lift forces. These forces cause tumor cells to be transported close to the floor of the chamber, while blood cells are carried about three cell diameters above them. The tumor cells are isolated by skimming them from the bottom of the chamber while the blood cells flow to waste. The principles, design, and modeling of the continuous-flow system are presented. To illustrate operation of the technology, we demonstrate the isolation of circulating colon tumor cells from clinical specimens and verify the tumor origin of these cells by molecular analysis. 相似文献
12.
Jinghui Luo Bahige G. Abdallah Gregory G. Wolken Edgar A. Arriaga Alexandra Ros 《Biomicrofluidics》2014,8(2)
Isolated mitochondria display a wide range of sizes plausibly resulting from the coexistence of subpopulations, some of which may be associated with disease or aging. Strategies to separate subpopulations are needed to study the importance of these organelles in cellular functions. Here, insulator-based dielectrophoresis (iDEP) was exploited to provide a new dimension of organelle separation. The dielectrophoretic properties of isolated Fischer 344 (F344) rat semimembranosus muscle mitochondria and C57BL/6 mouse hepatic mitochondria in low conductivity buffer (0.025–0.030 S/m) at physiological pH (7.2–7.4) were studied using polydimethylsiloxane (PDMS) microfluidic devices. First, direct current (DC) and alternating current (AC) of 0–50 kHz with potentials of 0–3000 V applied over a channel length of 1 cm were separately employed to generate inhomogeneous electric fields and establish that mitochondria exhibit negative DEP (nDEP). DEP trapping potential thresholds at 0–50 kHz were also determined to be weakly dependent on applied frequency and were generally above 200 V. Second, we demonstrated a separation scheme using DC potentials <100 V to perform the first size-based iDEP sorting of mitochondria. Samples of isolated mitochondria with heterogeneous sizes (150 nm–2 μm diameters) were successfully separated into sub-micron fractions, indicating the ability to isolate mitochondria into populations based on their size. 相似文献
13.
应用定量 X射线微区分析技术结合细胞化学技术 ,分析测定用单纯冷冻法保存离体猫肾脏过程中肾脏细胞的胞浆、线粒体、内质网、细胞核等细胞器内的 Ca2 浓度变化 ,并探索钙通道阻滞剂对这种变化的影响 .保存 36h及 72 h后 ,线粒体与胞浆中 Ca的峰背比极显著地提高 ,内质网、细胞核中 Ca颗粒减少 .添加 Verapamil后 ,保存过程中细胞器内 Ca2 无显著变化 .线粒体中的Ca峰背比与胞浆中的呈强的正相关 ,r=0 .990 .实验结果揭示 :保存过程中 ,Ca2 由 Ca库 (内质网等 )进入胞浆中 ,线粒体在胞浆 Ca2 浓度高时摄取 Ca2 ,而钙通道阻滞剂可抑制该过程 相似文献
14.
An integrated dielectrophoretic chip for continuous bioparticle filtering, focusing, sorting, trapping, and detecting 总被引：1，自引：0，他引：1
Multi-target pathogen detection using heterogeneous medical samples require continuous filtering, sorting, and trapping of debris, bioparticles, and immunocolloids within a diagnostic chip. We present an integrated AC dielectrophoretic (DEP) microfluidic platform based on planar electrodes that form three-dimensional (3D) DEP gates. This platform can continuously perform these tasks with a throughput of 3 μL∕min. Mixtures of latex particles, Escherichia coli Nissle, Lactobacillus, and Candida albicans are sorted and concentrated by these 3D DEP gates. Surface enhanced Raman scattering is used as an on-chip detection method on the concentrated bacteria. A processing rate of 500 bacteria was estimated when 100 μl of a heterogeneous colony of 107 colony forming units ∕ml was processed in a single pass within 30 min. 相似文献
15.
Narjes Allahrabbi Yi Shi Michelle Chia Mohammad S. M. Saifullah Kian-Meng Lim Lin Yue Lanry Yung 《Biomicrofluidics》2015,9(3)
Assessment of the microbial safety of water resources is among the most critical issues in global water safety. As the current detection methods have limitations such as high cost and long process time, new detection techniques have transpired among which microfluidics is the most attractive alternative. Here, we show a novel hybrid dielectrophoretic (DEP) system to separate and detect two common waterborne pathogens, Escherichia coli (E. coli), a bacterium, and Cryptosporidium parvum (C. parvum), a protozoan parasite, from water. The hybrid DEP system integrates a chemical surface coating with a microfluidic device containing inter-digitated microelectrodes to impart positive dielectrophoresis for enhanced trapping of the cells. Trimethoxy(3,3,3-trifluoropropyl) silane, (3-aminopropyl)triethoxysilane, and polydiallyl dimethyl ammonium chloride (p-DADMAC) were used as surface coatings. Static cell adhesion tests showed that among these coatings, the p-DADMAC-coated glass surface provided the most effective cell adhesion for both the pathogens. This was attributed to the positively charged p-DADMAC-coated surface interacting electrostatically with the negatively charged cells suspended in water leading to increased cell trapping efficiency. The trapping efficiency of E. coli and C. parvum increased from 29.0% and 61.3% in an uncoated DEP system to 51.9% and 82.2% in the hybrid DEP system, respectively. The hybrid system improved the cell trapping by encouraging the formation of cell pearl-chaining. The increment in trapping efficiency in the hybrid DEP system was achieved at an optimal frequency of 1 MHz and voltage of 2.5 Vpp for C. parvum and 2 Vpp for E. coli, the latter is lower than 2.5 Vpp and 7 Vpp, respectively, utilized for obtaining similar efficiency in an uncoated DEP system. 相似文献
16.
Dielectrophoresis (DEP) is employed to differentiate clones of mouse melanoma B16F10 cells. Five clones were tested on microelectrodes. At a specific excitation frequency, clone 1 showed a different DEP response than the other four. Growth rate, melanin content, recovery from cryopreservation, and in vitro invasive studies were performed. Clone 1 is shown to have significantly different melanin content and recovery rate from cryopreservation. This paper reports the ability of DEP to differentiate between two malignant cells of the same origin. Different DEP responses of the two clones could be linked to their melanin content. 相似文献
17.
Dielectrophoretic capture voltage spectrum for measurement of dielectric properties and separation of cancer cells 总被引：1，自引：0，他引：1
In this paper, a new dielectrophoresis (DEP) method based on capture voltage spectrum is proposed for measuring dielectric properties of biological cells. The capture voltage spectrum can be obtained from the balance of dielectrophoretic force and Stokes drag force acting on the cell in a microfluidic device with fluid flow and strip electrodes. The method was demonstrated with the measurement of dielectric properties of human colon cancer cells (HT-29 cells). From the capture voltage spectrum, the real part of Clausius-Mossotti factor of HT-29 cells for different frequencies of applied electric field was obtained. The dielectric properties of cell interior and plasma membrane were then estimated by using single-shell dielectric model. The cell interior permittivity and conductivity were found to be insensitive to changes in the conductivity of the medium in which the cells are suspended, but the measured permittivity and conductivity of cell membrane were found to increase with the increase of medium conductivity. In addition, the measurement of capture voltage spectrum was found to be useful in providing the optimum operating conditions for separating HT-29 cells from other cells (such as red blood cells) using dielectrophoresis. 相似文献
18.
Alternating current (AC) dielectrophoresis (DEP) experiments for biological particles in microdevices are typically done at a fixed frequency. Reconstructing the DEP response curve from static frequency experiments is laborious, but essential to ascertain differences in dielectric properties of biological particles. Our lab explored the concept of sweeping the frequency as a function of time to rapidly determine the DEP response curve from fewer experiments. For the purpose of determining an ideal sweep rate, homogeneous 6.08 μm polystyrene (PS) beads were used as a model system. Translatability of the sweep rate approach to ∼7 μm red blood cells (RBC) was then verified. An Au/Ti quadrapole electrode microfluidic device was used to separately subject particles and cells to 10Vpp AC electric fields at frequencies ranging from 0.010 to 2.0 MHz over sweep rates from 0.00080 to 0.17 MHz/s. PS beads exhibited negative DEP assembly over the frequencies explored due to Maxwell-Wagner interfacial polarizations. Results demonstrate that frequency sweep rates must be slower than particle polarization timescales to achieve reliable incremental polarizations; sweep rates near 0.00080 MHz/s yielded DEP behaviors very consistent with static frequency DEP responses for both PS beads and RBCs. 相似文献
19.
Leslie Y. Yeo 《Biomicrofluidics》2010,4(1)
This Special Topic section is a compilation of several original contributions covering both fundamental and practical aspects of electrokinetic microfluidic phenomena that were presented during the Electrokinetics and Microfluidics sessions held at the conference.Electrokinetics is currently the mechanism of choice for the manipulation of fluids as well as colloidal and biological particles at microscale and nanoscale dimensions.1 The popularity of electrokinetics is perhaps not so surprising as electrodes are easy to fabricate and embed into microfluidic chips, thus allowing the entire fluid and particle actuation mechanism to be completely integrated into the device. In addition, driving microfluidics with electric fields is relatively straightforward and allows for precise actuation. Nevertheless, considerable challenges remain in understanding the complex mechanisms associated with the hydrodynamics of conducting and dielectric fluids and particles under the influence of electric fields. Concomitantly, there has been an exponential increase in research and development in this field along both fundamental and applied themes in the past five years.This sustained growth in the microfluidics community of electrokinetics research has led to a sequel to the first Electrokinetic Phenomena and Microfluidics session at the 82nd ACS Colloid and Surface Science Symposium in Raleigh, NC, in 2008, and which we hope will now be a regular feature at successive ACS Colloid and Surface Science meetings. This year at the combined 2009 13th International Conference on Surface and Colloid Science (ICSCS) and the 83rd ACS Colloid and Surface Science Symposium in New York, the Electrokinetics and Microfluidics symposium proved to be extremely popular, with three keynote lectures presented by Professor Howard Stone, Professor Hsueh-Chia Chang, and Professor Thomas Healy, and 44 oral presentations. In both 2008 and 2009, Biomicrofluidics has organized a special issue to cover some of the contributions reported at these meetings.2The growing interest in using electric fields to manipulate biological entities such as cells, DNA, and even single molecules is reflected in this year’s collection of papers with dielectrophoretic (DEP) phenomena comprising the bulk of the contributions. In Ref. 3, a new theory to describe Stern layer conductance along the surface of nanocolloids is proposed, forming the basis for the derivation of a more accurate prediction of the DEP crossover frequency. This theory is then employed to determine the conformation and, hence, optimum coverage of oligonucleotides on the surface of nanocolloid functionalized molecular probes during DNA hybridization under the influence of DEP, which can be exploited for biomolecular sensing. Other fundamental DEP papers include the investigation of particle motion under DEP induced optically via a photoconductor, in which Zhu et al.4 characterized the frequency dependence of the motion through the synchronous velocity spectra of the particles, and a numerical study of particle trapping at the throat of converging-diverging microchannels under the influence of negative DEP using a transient arbitrary Lagrangian–Eulerian finite element method.5 A more practical implementation is, on the other hand, reported by Yang et al.6 in which the negative DEP is exploited to separate colorectal cancer cells from other cells in a microfluidic device as a demonstration of a portable cancer detection tool.Continuing along the separation theme, but with regard to DNA separation using pulsed-field gel electrophoresis aided by sparse but regularly ordered microfabricated arrays of nanoposts, is a Brownian dynamics simulation model reported by Ou et al.7 in which DNA channeling, which predicts that the motion of DNA is undisturbed by the presence of arrays for large spacing to DNA equilibrium size ratios and when the field lines are straight, is predicted, consistent with experimental observations. In another fundamental paper, a direct numerical simulation model is presented to predict the current-voltage relationship across conducting pores along cell membranes, which is of fundamental importance in the electroporation process.8We hope that you will enjoy reading the contributions in this special topic and that it encourages you to participate in future Electrokinetics and Microfluidics meetings at the ACS Colloid and Surface Science Symposia, which we definitely hope will continue on a regular basis. 相似文献
20.
Yanwei Huang Yu He Howard Sheng Xia Lu Haini Dong Sudeshna Samanta Hongliang Dong Xifeng Li Duck Young Kim Ho-kwang Mao Yuzi Liu Heping Li Hong Li Lin Wang 《国家科学评论(英文版)》2019,6(2):239
Lithium titanium oxide (Li4Ti5O12, LTO), a ‘zero-strain’ anode material for lithium-ion batteries, exhibits excellent cycling performance. However, its poor conductivity highly limits its applications. Here, the structural stability and conductivity of LTO were studied using in situ high-pressure measurements and first-principles calculations. LTO underwent a pressure-induced amorphization (PIA) at 26.9 GPa. The impedance spectroscopy revealed that the conductivity of LTO improved significantly after amorphization and that the conductivity of decompressed amorphous LTO increased by an order of magnitude compared with its starting phase. Furthermore, our calculations demonstrated that the different compressibility of the LiO6 and TiO6 octahedra in the structure was crucial for the PIA. The amorphous phase promotes Li+ diffusion and enhances its ionic conductivity by providing defects for ion migration. Our results not only provide an insight into the pressure depended structural properties of a spinel-like material, but also facilitate exploration of the interplay between PIA and conductivity. 相似文献