Archive for the ‘Hot Articles’ Category

Hooked on a Feeling: measuring cell-substrate adhesion with ISFET devices

By developing an ion-sensitive field-effect transistor with small gate dimensions, scientists at the University of Applied Sciences Kaiserslautern in Germany were able to measure cell-substrate adhesion on the single cell scale.

To survive, most mammalian cells attach to other cells and the extracellular environment in order to regulate their growth, proliferation, and migration. Electrical impedance spectroscopy is one way to quantitatively monitor cell-substrate interactions. The strength of cellular adhesion to a substrate with integrated electrodes can be measured by comparing the ratio of the readout voltage to the applied alternating current. Yet this method is limited groups of many cells as the size of the microelectrode must be larger than 100 μm in diameter. Smaller features are subject to greater interface impedance between the electrode and liquid media and this background impedance overwhelms the desired cell-substrate measurements. Suslorapova and colleagues thus used an ion-sensitive field-effect transistor (ISFET) with small gate dimensions to overcome this limitation. The group was able measure the effects of enzymatic digestion with trypsin and an apoptosis-inducing drug on single cell detachment using the ISFET devices with a 16 by 2 square micron gate.

The authors create an equivalent circuit model to interpret recorded impedance spectra from their single cell and small cell groups grown in contact with the field-effect transistor devices. The seal resistance and membrane capacitance parameters which can be extracted from the measured transistor transfer function (TTF) provide measures of cell shape and adhesion to the substrate. Changes in TTF correspond to adhesion of individual cells on top of the ISFET gates. This platform and the model developed to interpret TTF signal opens exciting avenues to monitoring cell adhesion in high throughput yet still at single cell resolution.

Download the full research paper paper for free* for a limited time only!

Electrical cell-substrate impedance sensing with field-effect transistors is able to unravel cellular adhesion and detachment processes on a single cell level
A. Susloparova , D. Koppenhöfer , J. K. Y. Law , X. T. Vu and S. Ingebrandt. Lab Chip, 2015, 15, 668-679. DOI: 10.1039/C4LC00593G

*Access is free until 27.03.15 through a publishing personal account. It’s quick, easy and free to register!

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January’s Free HOT Articles

These HOT articles, published in January 2015 were recommended by our referees and are free* to access for 4 weeks

Microfluidic single sperm entrapment and analysis
B. de Wagenaar, J. T. W. Berendsen, J. G. Bomer, W. Olthuis, A. van den Berg and L. I. Segerink
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01425A, Paper

Graphical abstract: Microfluidic single sperm entrapment and analysis

Optofluidic ultrahigh-throughput detection of fluorescent drops
Minkyu Kim, Ming Pan, Ya Gai, Shuo Pang, Chao Han, Changhuei Yang and Sindy K. Y. Tang
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01465K, Paper

Graphical abstract: Optofluidic ultrahigh-throughput detection of fluorescent drops

Hydrogel-droplet microfluidic platform for high-resolution imaging and sorting of early larval Caenorhabditis elegans
Guillaume Aubry, Mei Zhan and Hang Lu
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01384K, Paper

Graphical abstract: Hydrogel-droplet microfluidic platform for high-resolution imaging and sorting of early larval Caenorhabditis elegans

Take a look at our Lab on a Chip 2015 HOT Articles Collection!

*Access is free until 11.03.15 through a publishing personal account. It’s quick, easy and free to register!

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Culturing Cells on Druggable Bubbles

When testing the effects of drugs on cells and tissues, laboratory scientists generally use a pretty crude approach. They simply mix the desired concentration of the drug with the culture medium and then add it to separate plastic wells in which cells or tissues have been cultured. Of course, this approach has its limitations: when testing many different concentrations and mixtures of drugs, the amount of wells needed for an experiment grows very quickly to overwhelming numbers. Moreover, all of the drug is generally added at once, not taking into account the gradual pharmacokinetic profiles that you would normally find in the human body.

In a paper in Lab on a Chip, scientists from Corning, Inc. and Massachusetts General Hospital demonstrate a new, microengineered approach for treating cultured cells with drugs. Instead of growing the cells on flat surfaces, cells are grown on micro-modified wells plates that contain regular patterns of tiny holes. The microholes can be filled with dried-up drug and then sealed off with a semi-permeable layer of collagen. When cells are grown on the collagen, culture medium starts seeping into the air-filled microholes. The dried-up drug then dissolves and diffuses through the collagen layer, exposing the microscopic patch of cells around the microhole to the drug (see also the figure below).

A schematic overview of how to will microwells with drug and culture hepatocytes on them

The authors only show the results of a simple proof-of-principle experiment with Nefazodone-filled holes leading to local toxicity for cultured liver cells. The technique looks promising however, and it will be interesting to see further development. How easy will it be to load holes with different concentrations and mixtures of drugs? Can the process of drugs diffusing into the medium be controlled? Can we control time-release profiles by changing the shape of the holes, by changing the surface properties of the holes, or maybe by changing the gas content of the medium?

It will also be interesting to see whether the technique can be combined with high-throughput imaging, like fluorescence microscopy or scanning electrochemical microscopy as was recently shown for cells in microscopic wells by Sridhar, et al.

Make sure to check out the paper by Goral, et al. in which they outline their technique while it is still free* to access.

*Access is free until 9.03.15 through a publishing personal account. It’s quick, easy and free to register!

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December’s Free HOT Articles

These HOT articles, published in December 2014 were recommended by our referees and are free* to access for 4 weeks

Metal-Amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA)
Anand Bala Subramaniam, Mathieu Gonidec, Nathan D. Shapiro, Kayleigh M. Kresse and George M. Whitesides
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01161A, Paper

Graphical abstract: Metal-Amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA)

High process yield rates of thermoplastic nanofluidic devices using a hybrid thermal assembly technique
Franklin I. Uba, Bo Hu, Kumuditha Weerakoon-Ratnayake, Nyote Oliver-Calixte and Steven A. Soper
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01254B, Paper

Graphical abstract: High process yield rates of thermoplastic nanofluidic devices using a hybrid thermal assembly technique

Real-time tracking, retrieval and gene expression analysis of migrating human T cells
Matthias Mehling, Tino Frank, Cem Albayrak and Savaş Tay
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01038H, Paper

Graphical abstract: Real-time tracking, retrieval and gene expression analysis of migrating human T cells

Take a look at our Lab on a Chip 2014 HOT Articles Collection!

*Access is free until 2.02.15 through a publishing personal account. It’s quick, easy and free to register!

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Saving Stripes: using gratings to prevent destructive air-water interfaces

Researchers at National Taiwan University design grating structures to prevent air-water interfaces from destroying lipid bilayers, enabling robust bioassays of synthetic membranes.

Supported lipid bilayers (SLBs) are useful as platforms to simulate cell membranes for evaluating transport of toxins and viral particles1 and screening new pharmaceutical reagents. Yet a significant challenge is maintaining the integrity of SLBs throughout an experiment. Air-water interfaces, commonly formed during reagent changes and rinses, peel apart SLBs and delaminate them from the substrate. Strategies to preserve SLB integrity involve coating SLBs with polymers to increase their rigidity or adding proteins and sugars to form protective layers with a high bending modulus above the membrane. These methods modify the chemical structure and environment of SLBs, preventing analysis of membrane properties and specific assays of membrane-tethered species. Thus, Chung-Ta Han and Ling Chao developed a substrate with patterned gratings to prevent air-water interfaces from directly contacting SLBs when an air bubble is introduced into a microchannel with SLBs.Han2015_Figure2

The grating structures, fabricated by standard photolithography, are perpendicular to fluid flow in the microchannel and act as obstacles to air-water interfaces contacting SLBs directly by a ‘tenting’ mechanism (see figure at right). Holding the obstacle height constant at 2 μm, Han and Chao evaluated obstacle spacing at different flow rates influenced SLB stability after treatment with an air bubble. 40 μm spacing was found to efficiently preserve SLBs from air-water interfaces at a practical range of flow rates: 60 – 6000 mm/min. The authors also confirmed the integrity of the membranes by comparable diffusivity measurements within the SLBs before and after air-bubble treatment. Finally, the authors demonstrated that air bubbles did not affect receptor-ligand interactions between species embedded in the SLBs and surrounding buffer when SLBs were protected using the microfabricated obstacles.

This platform uses integrated barriers to protect SLBs from air-water interfaces, creating SLBs with native properties to study biomolecule behavior within membranes and perform high throughput analytical assays utilizing synthetic membranes.

Download the full article now – free* access for a limited time only!

Using a patterned grating structure to create lipid bilayer platforms insensitive to air bubbles
Chung-Ta Han and Ling Chao. Lab Chip, 2015, 15, 86 – 93.
DOI: 10.1039/c4lc00928b
[1] I. Kusters, A. M. Van Oijen and A. J. Driessen, ACS Nano, 2014, 8, 3380-3392.

*Access is free until 06.02.15 through a registered RSC Publishing account.

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Cytometry Unplugged: acoustophoretic focusing enables impedance-based particle sizing and counting

Groups collaborating across Sweden, Denmark, and Korea develop a chip-integrated acoustic focusing technique to precisely arrange particles for fast sizing and counting using impedance analysis.

The size and number of particles in a mixture can be quickly determined using a Coulter counter. Changes in resistance across a Coulter counter orifice through which particles pass correspond to the volume particles occupy as they displace the ionic carrier fluid (impedance spectroscopy). As fabrication methods transition to planar electrode formats to facilitate device development, the precise position of particles in the orifice becomes crucial to obtaining accurate results. Using planar electrodes on the channel bottom, the electric field across the orifice varies and thus sizing information from amplitude changes in impedance depend on consistent particle positioning. Previous methods using fluid flow focusing require complex fabrication steps and suffer from ion diffusion between virtual channel boundaries (fluid-fluid interfaces). Thus, Carl Grenvall in the Biomedical Engineering department in Lund University and his colleagues developed an acoustic actuation method to focus particles into the middle of the channel before they pass into the sensing aperture containing planar electrodes.

The team used two different frequencies to form standing waves in horizontal and vertical directions of the ‘prefocusing channel’ to guide particles to the center of the aperture where impedance was analyzed. Concentration studies helped determine the optimal density of particles to enable rapid sample analysis yet prevent formation of doublets. Confocal imaging confirmed simulation results to show distribution of focused particles and narrow confinement – 2.04% coefficient of variation after removing doublets, which is on par with other experimental and commercial cytometry platforms. The group was able to discriminate particle sizes from 3, 5, and 7 μm as well as separate 7 μm beads in a diluted blood sample. This demonstration of efficient particle focusing in two dimensions is an exciting development to create integrated simple-to-manufacture microchip impedance microscopy platforms. Standing wave acoustophoresis is gentle on cells as several studies even reporting in-field cell culturing1, thus suggesting further opportunities for integration of microscale cytometers into microscale experimental platforms.

Download the full paper for free* for a limited time only!

Two-dimensional acoustic particle focusing enables sheathless chip Coulter counter with planar electrode configuration
Carl Grenvall, Christian Antfolk, Christer Zoffmann Bisgaard, and Thomas Laurell. Lab Chip, 2014, 14, 4629 – 4637.
DOI: 10.1039/c4lc00982g

*Access is free through a registered publishing personal account until 03/02/2015.

[1] M. A. Burguillos, C. Magnusson, M. Nordin, A. Lenshof, P. Augustsson, M. J. Hansson, E. Elmer, H. Lilja, P. Brundin and T. Laurell, PloS one, 2013, 8, e64233.

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Measuring Electrical Resistance in Organs-on-Chips

The human body contains many barriers, like the skin, the wall of blood vessels, or the lining of the intestine. Understanding and quantifying the barrier function of human tissues is of great biomedical importance. Just think of wounds, hemorrhage, pulmonary edema and intestinal infections. All of them involve the breakdown of a barrier in the human body.

The quantification of barrier function of cell layers can be carried out in the laboratory by measuring their resistance to an electrical potential difference. When applying such a potential difference over a layer of tissue, ions in the solution start moving, which leads to an electrical current. The tighter the tissue barrier, the more difficult it is for ions to pass through, the higher the electrical resistance will be. Measuring the electrical resistance of cell layers is a popular tool in conventional cell culture. However, it has proven difficult to use the same tool in microfluidic cell culture systems, such as organs-on-chips.

Measuring electrical resistance of cell layers in organs-on-chips is difficult, because the devices only contain small amounts of water and ions, which means they will have a very high electrical resistance to begin with. This means that the resistance of a layer of cells is only a very small portion of the total resistance of the system. But even when being careful to perform a measurement that is sensitive enough to detect the small contribution of the cell layer to the total system resistance, it turns out that the resistance values for cells in such small devices don’t match the values that we find in conventional cell culture systems.

In a recent paper in Lab on a Chip, written by dr. Mathieu Odijk, myself and others, we show that the apparent electrical resistance of a cell layer in an organ-on-a-chip will be much higher than that of a cell layer in a conventional cell culture system. The underlying cause for this high apparent electrical resistance is rooted – again – in the high electrical resistance of microfluidic compartments.

Schematic depiction of current distribution through a cell layer in an organ-on-a-chip

An electrical potential that is applied at the start of a microfluidic compartment will drop significantly over the length of that compartment. This means that large parts of a cell layer that separates two microfluidic compartments will not be exposed to a significant potential difference anymore (see also schematic image on the left). Because we effectively only measure small parts of the cell layer and because small areas will by definition not conduct as much current as large areas, we will find a pretty high apparent value for the electrical resistance of the cell layer in an organ-on-a-chip. If we then make the mistake of assuming that this electrical resistance is produced by a barrier to which all cells in the layer have contributed equally, we will overestimate the tightness, resistance, barrier function of this cell layer.

Fortunately, the issue of overestimating the electrical resistance of cell layers in organs-on-chips can be resolved by calculating the effective area of the cell layer that contributes to the measured resistance. We apply this method to normalize the electrical resistance signal produced by a layer of epithelium in an organ-on-a-chip systems that mimics the human intestine. We show that after normalization, the resistance of the epithelium in this ‘gut-on-a-chip’ is the same as the resistance values that were found in standard cell culture systems.

Measuring barrier function in organs-on-chips is still tricky business, but the work in this article brings reliable measurements a step closer. Go check it out:

Odijk, et al. Measuring direct current trans-epithelial electrical resistance in organ-on-a-chip microsystems.

Access is free through a registered publishing personal account until 02/02/2015.

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November’s Free HOT Articles

These HOT articles, published in Novemeber 2014 were recommended by our referees and are free* to access for 4 weeks

From cellular lysis to microarray detection, an integrated thermoplastic elastomer (TPE) point of care Lab on a Disc
Emmanuel Roy, Gale Stewart, Maxence Mounier, Lidija Malic, Régis Peytavi, Liviu Clime, Marc Madou, Maurice Bossinot, Michel G. Bergeron and Teodor Veres
Lab Chip, 2015,15, 406-416
DOI: 10.1039/C4LC00947A, Paper

Inkjet-printed microelectrodes on PDMS as biosensors for functionalized microfluidic systems
Jianwei Wu, Ridong Wang, Haixia Yu, Guijun Li, Kexin Xu, Norman C. Tien, Robert C. Roberts and Dachao Li
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01121J, Paper


Electrochemical pesticide detection with AutoDip – a portable platform for automation of crude sample analyses
Lisa Drechsel, Martin Schulz, Felix von Stetten, Carmen Moldovan, Roland Zengerle and Nils Paust
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC01214C, Paper


Take a look at our Lab on a Chip 2014 HOT Articles Collection!

*Access is free until 23.01.15 through a publishing personal account. It’s quick, easy and free to register!

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Shrinking Lab-on-a-Chip to Lab-in-a-Tube

Throughout a series of Lab on a Chip Focus Articles Samuel Sánchez, research group leader at Max Planck Institute for Intelligent Systems and recently elected as “innovator of the year 2014”, will be highlighting cutting-edge reports based on miniaturized devices that bridge functional materials and bio-related applications. And first up we have…Lab-in-a-Tube!

Lab-on-a-chip already scales down several components and integrates them into one device, but now scientists are working toward shrinking this further to develop entire laboratories inside an ultra-compact architecture such as a small tube. Samuel discusses the concept and advantages of the lab-in-a-tube before highlighting remarkable cell studies that have already been performed using microtubes.

Lab-in-a-tube systems can combine several functionalities such as optical or electrochemical sensing and is therefore used in various detection systems. Samuel describes the developments in this area, leading to the fabrication of a highly sensitive rolled-up optofluidic ring resonator – fully integrated into lab-on-a-chip devices of course!

Label-free detection systems using the lab-in-a-tube concept

Finally, Samuel discusses the challenges of controlling fluid flow at the micro scale and the use of self-powered on-chip micropumps. As one of Samuel’s main interests, catalytic micropumps will be discussed further in an upcoming Focus Article.

Samuel’s full article ‘Lab-in-a-tube systems as ultra-compact devices’ can be downloaded for free* on our website. We hope you enjoy reading his summary of recent advances in this new and exciting concept of chip integration.

Don’t miss Samuel’s next focus article – register for our e-alerts now!

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More about Samuel Sánchez

Samuel earned his PhD in Analytical Chemistry from the Autonomous University of Barcelona in 2008. After a short period as an Assistant Professor, he worked in Japan at the National Institute for Materials Science. In 2010 he moved to the Institute for Integrative Nanoscience at the Leibniz Institute in Dresden where he was leading the “Biochemical Nanomembranes” group. He is now leading the independent research group at the Max Planck Institute for Intelligent Systems. Samuel has received several awards for his work including the Guinness World Record® for “The smallest man-made jet engine” in 2010, the IIN-IFW Research Prize 2011, the ERC-Starting Grant 2012 “Lab-in-a-tube and Nanorobotic Biosensors (LT-NRBS).” Recently, Samuel has been named as Spain’s top innovators under 35 by the Spanish edition of the journal MIT Technology Review.

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October’s HOT Free Articles

These HOT articles, published in October 2014 were recommended by our referees and are free* to access for 4 weeks

Optofluidic lasers with a single molecular layer of gain
Qiushu Chen, Michael Ritt, Sivaraj Sivaramakrishnan, Yuze Sun and Xudong Fan
Lab Chip, 2014,14, 4590-4595
DOI: 10.1039/C4LC00872C, Communication

A self-powered one-touch blood extraction system: a novel polymer-capped hollow microneedle integrated with a pre-vacuum actuator
Cheng Guo Li, Manita Dangol, Chang Yeol Lee, Mingyu Jang and Hyungil Jung
Lab Chip, 2015, Advance Article
DOI: 10.1039/C4LC00937A, Paper


Design of a 2D no-flow chamber to monitor hematopoietic stem cells
Théo Cambier, Thibault Honegger, Valérie Vanneaux, Jean Berthier, David Peyrade, Laurent Blanchoin, Jerome Larghero and Manuel Théry
Lab Chip, 2015,15, 77-85
DOI: 10.1039/C4LC00807C, Paper


Take a look at our Lab on a Chip 2014 HOT Articles Collection!

*Access is free until 5.01.14 through a publishing personal account. It’s quick, easy and free to register!

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