Lab on a Chip Blog

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

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

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

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!

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.

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.

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.

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

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!

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!

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

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

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!

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

1000-fold sample focusing on paper-based microfluidic devices
Tally Rosenfeld and Moran Bercovici
Lab Chip, 2014,14, 4465-4474
DOI: 10.1039/C4LC00734D

A reliable and programmable acoustofluidic pump powered by oscillating sharp-edge structures
Po-Hsun Huang, Nitesh Nama, Zhangming Mao, Peng Li, Joseph Rufo, Yuchao Chen, Yuliang Xie, Cheng-Hsin Wei, Lin Wang and Tony Jun Huang
Lab Chip, 2014,14, 4319-4323
DOI: 10.1039/C4LC00806E

Application of an acoustofluidic perfusion bioreactor for cartilage tissue engineering
Siwei Li, Peter Glynne-Jones, Orestis G. Andriotis, Kuan Y. Ching, Umesh S. Jonnalagadda, Richard O. C. Oreffo, Martyn Hill and Rahul S. Tare
Lab Chip, 2014,14, 4475-4485
DOI: 10.1039/C4LC00956H

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

*Access is free until 28.11.14 through a publishing personal account. It’s quick, easy and free to register!

Collaborators across the University of Augsburg, Harvard University, and the University of Glasgow create a fluorescence-activated cell sorter relying on acoustofluidics to guide particles to their final location.

Traditional fluorescence-activated cell and droplet sorting (FACS, FADS) machines are expensive and require considerable time for analysis as well as maintenance (i.e., rinsing and cleaning of tubing to prepare for RNase-free processing). Cheap and disposable microfluidic devices can alleviate the expense and maintenance required, but still lag in particle sorting speed because they depend on fluidic, dielectric, and magnetic actuation to direct particles after fluorescence interrogation.

Lothar Schmid, David Weitz, and Thomas Franke overcame these issues by using traveling surface acoustic waves (SAWs) to drive particles into select channels based on readout of a fluorescent signal. The group oscillated PDMS structures from below by embedded interdigitated transducers to achieve focused acoustic radiation forces which gently moved droplets and cells via acoustic streaming.

The group was able to achieve sorting independent of cell size and compressibility on the order of 3000 particles/second into multiple outlet channels. This fast separation of particles given fluorescence signal readout enables efficient sorting of populations which vary widely in shape and volume. Further, the particles did not have to be first encapsulated into drops. This simplification avoids biohazard aerosol formation, provides higher signal to noise on the fluorescent signal interrogation, and streamlines the separation process. The group demonstrated gentle sorting of melanoma cells in a single fluid based on metabolic activity and membrane integrity. It will be exciting to see how acoustic streaming can further be used to direct particles to aid rare cell separations and cell isolations from complex samples.

You can download the full article for free* until the 24th October 2014:

Sorting drops and cells with acoustics: acoustic microfluidic fluorescence-activated cell sorter
Lothar Schmid, David A. Weitz, and Thomas Franke. Lab Chip, 2014, 14, 3710-3718.
DOI: 10.1039/C4LC00588K

*Access is free through a registered RSC account – click here to register

Researchers at Virginia Tech create an elegant device to perform DNA amplification starting from whole cells by taking advantage of diffusivity differences in PCR components.

Diffusion can be friend or foe in the microscale regime, depending on the application. For active mixing, relying on diffusion can lengthen reaction time and thereby decrease reaction efficiency. But for separating reaction products, low ratios of convection to diffusion (Péclet number) enable control over elements based on their diffusivity^[1]. Professors Luke Achenie and Chang Lu from the chemical engineering department at Virginia Tech took advantage of this diffusion-enabled control to combine cell lysis and PCR reactions in ‘one pot’ with temporal separation of how components add to the chamber due to diffusivity differences. Separation of cell lysis and DNA amplification steps in PCR is important as many traditional chemical reagents for cell lysis inhibit polymerases used in PCR and Phusion polymerases tolerant to surfactant lysis reagents are incompatible with downstream SYBR green dyes.

The device consists of a single reaction chamber connected on both sides to two separate loading chambers. A hydration line ensures minimal evaporation during the PCR cycle in the main chamber. The loading chambers are opened in sequence to let molecules into the reaction chamber via two-layer control valves. The substantial difference in reagent diffusivity in the lysis and amplification processes allow diffusion gradients to drive molecules from new solutions contacting the reaction chamber and replace reagents from previous steps without disturbing the DNA of interest. Taq polymerase and proteins are two orders of magnitude larger in diffusivity than typical (50 kb) DNA fragments, while primers, dNTPs, and lysis buffers are three orders smaller. Relying solely on diffusion to deliver reagents to the main chamber increases the time of the reaction, but this can be addressed by elevating the temperature or increasing concentration of starting reagents in the loading chambers.

The authors showed the functionality of their device with purified human genomic DNA as well as single cells. This work opens up new capabilities to perform multi-step preparation and amplification assays for DNA in a single chamber starting directly from few cells to a single cell.

Download the full article today – for free*

Diffusion-based microfluidic PCR for “one-pot” analysis of cells

Sai Ma, Despina Nelie Loufakis, Zhenning Cao, Yiwen Chang, Luke E Achenie and Chang Lu
DOI:10.1039/C4LC00498A

References: [1] T. M. Squires and S. R. Quake, Reviews of Modern Physics, 2005, 77, 977.

*Access is free through a registered RSC account until 19th September 2014 – click here to register

About the Webwriter

Sasha is a PhD student in bioengineering working with Professor Beth Pruitt’s Microsystems lab at Stanford University. Her research focuses on evaluating relationships between cell geometry, intracellular structure, and force generation (contractility) in heart muscle cells. Outside the lab, Sasha enjoys hiking, kickboxing, and interactive science outreach.