Author Archive

MicroTAS 2018 Highlights

The 22nd International Conference on Miniaturized Systems for Chemistry and Life Sciences (aka MicroTAS) was held last year in Kaohsiung, Taiwan. Welcoming more than 1000 participants, MicroTAS 2018 conference brought together several disciplines including microfluidics, microfabrication, nanotechnology, integration, materials& surfaces, analysis & synthesis, and detection technologies for life sciences & chemistry. Besides the exciting scientific program and great presentations, social/networking events (welcome reception, student mixer, women night out, and conference banquet) have made MicroTAS 2018 conference an unforgettable one. In this article, we would like to share some of the conference highlights with our Lab on a Chip blog readers.

 

 

Unraveling endothelial cell phenotypic regulation by spatial hemodynamic flows with microfluidics 

Sarvesh Varma, Guillermo Garcia-Cardena, & Joel Voldman

Did you know that artery bifurcations are prone to atherosclerosis? Blood flow profiles in vessels can help us to gain insights towards atherosclerosis. In this work, the authors fabricated a soft microdevice to study the effects of helical and chaotic flows on endothelial cells located in vein walls. They hypothesized and demonstrated that a helical (uniform) flow profile results in endothelial cells aligning upstream to flow and gain atheroprotective properties, while the chaotic flow results in misalignment of cells that give rise to atherosclerosis.

The figure shows the morphological adaptations of cells in response to distinct spatial flows, scale bars are 0.1 mm.

 

 

glass-like polymer

 

3D printing of microfluidic glass reactors 

Patrick Risch, Frederik Kotz, Dorothea Helmer & Bastian Rapp

Microfluidic devices are mostly made from PDMS, although this material is not always well-suited for thermal, optical, mechanical and chemical changes. In this work, the authors present a new resin formulation to inspire the 3D printing of glass, which is more durable than PDMS. The resin was fabricated using stereolithography printer and this technique is useful for rapid prototyping of microfluidic devices made from glass for optical detection or chemical reaction applications.

A 3D gradient generator is shown in this figure, scale bar is 2 mm.

 

A Tetris-like modular microfluidic platform for mimicking multi-organ interactions 

Louis Ong Jun Ye, Terry Chng, Chong Lor Huai, Seep Li Huan & Toh Yi-Chin

Modularization is undoubtedly on the rise in microfluidics and this work demonstrates an interesting approach. The authors focused on solving ‘limited compatibility with existing devices‘ problem. To achieve that, ring magnets were utilized to connect different parts of PDMS building blocks that were previously fabricated using micro molds. A modular platform assembled using this approach was shown to culture cells as a proof-of-concept study. The platform is expected to allow facile configuration of complex experimental set-ups involving multiple tissues.

The image shows a modular device (left), and its parts (right) connected each other via magnets, scale bars are 1 cm.

 

 

A magneto-switchable superhydrophobic surface for droplet manipulation

Chao Yang & Gang Li

Surface hydrophobicity is an important feature when it comes to bio and chemical applications. In this work, magneto switchable micro-pillars were made from PDMS and carbonyl iron particles. The pillars erect under influence of a magnetic field, resulting in subsequent switching of the wettability and adhesion of the surface between the water-repellent and water-adhesive states. The surface becomes superhydrophobic (water-repellent) when the magnetic field is applied. The authors demonstrated droplet lifting and transportation on a surface using this approach.

The image depicts the effect of an external magnetic field on the stiffness of micro-pillars.

 

About the Web writer

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include the development of microfluidic devices for quantitative analysis of proteins from single-cells, next-generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Simple microfluidic cell sorter device to replace manual tissue dissociation protocols

Even a tiny group of cells has the ability to populate a tumor in tissues. Determining cellular diversity and identifying these small cell groups gains importance when it comes to selection of treatment strategies. Tissue samples taken from patients are required to be dissociated into single-cell suspensions, therefore identification can be efficiently done at single-cell level using a powerful suite of technologies including flow cytometry, mass cytometry, and single cell RNA sequencing. However, breaking a tissue down to a single-cell suspension is not an easy task. The old-school way is to cut the tissue sample into small pieces with a blade and mechanically dissociated by vigorous shaking after the application of proteolytic enzymes. Large aggregates are removed by filtering the suspension through a strainer. This technique significantly increases the sample loss, drops the speed of the process and is not ideal for immediate downstream analysis.

In this month’s Lab on a Chip HOT article series, a group of researchers led by Dr Jered Haun at University of California Irvine presented a novel and simple approach that improves the quality of single-cell suspensions obtained from tissue samples using microfluidics. Jeremy Lombardo, a co-author of this article, explains that “the goal of this work was to fully replace manual intensive tissue dissociation protocols by using microfluidic devices.” The developed tool is a microdevice consisting of two nylon membranes, one with 25-50 µm mesh, and the other with 10-15 µm mesh, attached to micron-sized pores and microchannels. The device is made of laser-micromachined hard plastic (PET, aka. polyethylene terephthalate), which enables operation at high flow rates (>10 mL/min) when compared to PDMS (a silicon-based organic material). Also, the chip has multiple layers for connecting nylon mesh membranes at different levels (Figure 1).

cell sorter

Figure 1. Microfluidic cell sorter device for tissue  samples. The sketch shows the inner layers, consisting of two membranes for operating the device in direct or tangential filtration modes. Membrane mesh size can be adjusted to the cell size. Micrographs on the right show lattice network with several pore sizes used in this work. Pore sizes are (top to bottom) 50, 25, 15, 10 µm diameter.

Working principle of the cell sorter device

The inlet of the device connects to a microporous membrane to introduce tissue samples. The Sample passing through the membrane exits through the effluent outlet. It is also possible to direct a portion of the sample along the surface of the membrane that is connected to the cross-flow outlet. The device is either operated in a direct filtration regime to maximize sample recovery and processing speed, or in a tangential filtration regime to sweep larger tissue fragments and cell aggregates away to prevent clogging.

While the researchers initially hypothesized that under pressure-driven flow, cell and tissue aggregates might disaggregate as they pass through the membranes of the device, they were pleasantly surprised by the drastic level of single cell increases seen in the initial testing of these devices, says Jeremy Lombardo and adds “The hardest part in developing and testing this device was to find a combination of membrane pore sizes that could best dissociate cell aggregates and tissue without compromising cell viability. Thorough testing of various pore sizes and combinations were ultimately carried out with both cell line and murine tissue models before we settled on the final 50 and 15 μm pore sizes.”

Advantages, challenges and the future

The authors summarized the advantages of this platform for Lab on a Chip blog readers: “The device is extremely simple to operate as well as inexpensive to fabricate. It can easily be incorporated into many tissue dissociation applications for improved single cell yields as a standalone device but could also be easily integrated with other downstream microfluidic operations (cell sorting, detection etc.).” According to the authors, “in the current format of cell sorter device, cells that are very large in size would likely be difficult to process, as they would likely span multiple pores of the filters and be traditionally filtered away instead of dissociated.” Although seeming like a challenge, this can easily be addressed by adjusting the filter membrane pore sizes to accommodate these larger cell types.

For the future of the device, the authors indicate, “We are also currently working on integrating this device with upstream, larger scale tissue dissociation devices that we have developed previously to create a fully automatable microfluidic tissue dissociation platform.

 

To download the full article for free* click the link below:

Microfluidic filter device with nylon mesh membranes efficiently dissociates cell aggregates and digested tissue into single cells
Xiaolong Qiu, Jeremy A. Lombardo, Trisha M. Westerhof, Marissa Pennell, Anita Ng, Hamad Alshetaiwi, Brian M. Luna, Edward L. Nelson, Kai Kessenbrock, Elliot E. Hui, and Jered B. Haun
Lab Chip, 2018, Lab on a Chip Recent Hot Articles
DOI: 10.1039/c8lc00507a

About the Webwriter
Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

How soil-worms allow for realistic human physiology studies

Mice, fruit fly, zebra fish easily come to mind when thinking of animal models for human physiology studies – but one animal is often forgotten, although it is as functional as the others. Have you guessed already? We are talking about soil-dwelling worms, aka C. elegans! These animals combine the simplicity of single-cell systems with the complexity of animal models, therefore they can provide significant insights into human disorders. Please take a moment to look at our note below summarizing the key features of C. elegans.

Muscular strength is a good example of human physiology studies  and it relies on calcium-initiated muscle contraction, sarcomere composition and organization, and translocation of actin and myosin molecules. Analysis of such parameters can reveal the formation of muscular dystrophy, a muscle degenerative disorder. However, the measurement of these parameters has been a challenge due to the dependence on random animal-behavior that yields irreproducible results. Recently, researchers from Texas Tech University collaborated with Rutgers University and University of Nottingham to study muscular strength in C. elegans. They achieved to obtain results independent of animal behavior and gait in a miniature system consisting of an elastic micropillar forest (Figure 1a and 1b).

The microfluidic system is made of PDMS, and contains bendable micropillars hanging from the microchannel ceiling. The pillars are bent upon the action of the body muscles when C. elegans crawls through the pillar array. Individual pillar bending events can be quantified using a microscope-camera system and image analysis (Figure 1c). The pillar density is designed to create high mechanical resistance to locomotion, therefore maximum exertable force can be measured independent of animal behavior. Here, maximum exertable force corresponds to the peak force exerted by human quadriceps muscle in a standardized knee extension resistance test.

Figure 1. (a) Image of the microfluidic device with the pillar forest and the ports. (b) Schematic demonstration of the C. elegans strength measurement apparatus. Inset shows a scanning electron microscope picture of the pillars. (c) A sketch of interaction with a pillar by the worm body. The pillar is bent due to the action of the body muscles (shown in red and green). Image from Rahman et al.

The authors of this study explain that animals produce strong forces in highly resistive areas and demonstrate different locomotion regimes based on the body size relative to gap between pillars. Besides the body size, body configuration and behavioral characteristics can be the sources to the magnitude of the force exerted on the pillars. Thanks to the probabilistic nature of the parameters sourcing of the force exerted, a reproducible algorithm can be defined for quantifying muscle strength. Using this strategy, researchers showed for the first time that locomotion between microfluidic pillars comprises of three regimes: non-resistive (worm contacts with 1-2 pillars and doesn’t adjust body posture), moderately resistive (worm contacts with >2 pillars and minimally adjust body posture), and highly resistive (worm contacts with multiple pillars and body posture adjustment is disabled). When operated at highly-resistive regime, the microfluidic system suppresses the animal behavior. This system allows for (1) discriminating between the muscle strength or weakness levels of individual worms of different ages, (2) determining body length decrease and muscular contraction levels led by levamisole treatment, (3) comparing the muscular strength in the wild and mutant C. elegans types. According to the researchers, the future studies can help us to obtain deeper understanding in molecular and cellular circuits of neuromuscular function as well as dissection of degenerative processes in disuse, aging, and disease.

To download the full article for free* click the link below:

NemaFlex: a microfluidics-based technology for standardized measurement of muscular strength of C. elegans
Mizanur Rahman, Jennifer E. Hewitt, Frank Van-Bussel, Hunter Edwards, Jerzy Blawzdziewicz, Nathaniel J. Szewczyk, Monica Driscolld, and Siva A. Vanapalli
Lab Chip, 2018, Lab on a Chip Recent Hot Articles
DOI: 10.1039/c8lc00103k

 

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

What we know about cancer tumors

Cancer tumors are a lot more complex than we think: besides cancer cells, supportive tissue cells, fat, and even immune cells can be found in a tumor. Combined crosstalk in between these cell groups influences the way the tumor develops or responses to drug treatment. On the other hand, the majority of what we know about cancer tumors has been acquired by studying cell ensembles. Recent strides to improve our understanding of cancer revealed that we have long been missing the stochastic interactions and rare events due to ensemble-average measurements. We can unveil how these cell groups work together and how the rare events change the fate of a tumor thanks to single-cell analysis techniques.

Single cells can be identified by extrinsic and intrinsic markers. Extrinsic markers are definitive of genetic and proteomic states of a cell. Flow cytometry and mass spectrometry have been the workhorse of extrinsic marker analysis, where genetic or proteomic materials are often fluorescently labeled for detection. With these techniques, multiplexed analysis of thousands of cells can be employed simultaneously. Intrinsic markers include size, shape, density, optical, mechanical, and electrical properties which do not require labelling. Microfluidic techniques provide with a plethora of different functionalities to sort the cells based on intrinsic markers. Combination of both extrinsic and intrinsic data advances our understanding of how cell heterogeneity is reflected in cell-to-cell variations in tumor development and drug-response. Although many powerful methods are available for determining extrinsic markers, not many techniques can gather information about a panel of different intrinsic markers.

A recent study from Biological Microtechnology and BioMEMS group at MIT represents an important microfluidic approach for the development of multiparameter intrinsic cytometry tool. The approach includes several different microfluidic modules combined with microscope imaging and image processing by machine learning. Separate modules measuring cell size, deformability, and polarization can be combined and organized within the tool (Figure 1). (i) Size module detects the cell size optically in a flow through system. Cell size module is necessary to separate different cell types that can give important cues about disease state. (ii) In deformability module, cells pass through narrow channels, and their transit time defines the deformability. Cell deformability gives cues about cytoskeletal and nuclear changes associated with cancer progression. (iii) In the polarization module, dielectrophoretic force at a fixed frequency is applied on cells driven by opposing hydrodynamic forces. Cells approach coplanar electrodes with different equilibrium positions depending on their polarizability. Cell polarizability allows for distinguishing subtle changes in biological phenotypes. As a proof-of-concept work, drug-induced structural changes in cells were detected for the first time using five different intrinsic markers, including size, deformability, and polarizability at three frequencies. The authors indicate that this powerful tool can further be equipped with visual readout capabilities, such as deterministic lateral displacement array, inertial microfluidics, acoustophoresis, optical techniques.

Figure 1. Multiparameter intrinsic cytometry combines different microfluidic modules on one substrate along with cell tracking to correlate per-cell information across modules for different intrinsic properties including size, polarizability, and deformability.

 

To download the full article for free* click the link below:

Multiparameter cell-tracking intrinsic cytometry for single-cell characterization
Apichitsopa, A. Jaffe, and J. Voldman
Lab Chip, 2018, Lab on a Chip Recent Hot Articles
DOI: 10.1039/C8LC00240A

*Article free to read until 31st August 2018

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing,compartmentalized organ-on-chip studies, and desalination of water on the microscale.

 

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Microparticles: Good things come in small packages

Microparticles were first described in 1967 by Peter Wolf, a physician, as ‘minute particulate materials’ when he investigated the platelet activity in human plasma. They were initially used as drug delivery agents because their size is as small as pollens, which can easily go into the human body. Not long after the great promise of microparticles has been realized, and today we use microparticles in numerous applications including pharmaceuticals, biomedicine, bioengineering, cosmetics, printing, and food science. The widespread use is not a coincidence, they can be synthesized from a multitude of materials, i.e. metal, polymer, gel etc. Especially, polymer microparticles, conferring a great versatility in size, shape, and chemistry, gained more attention in industry. Just like their usage areas, fabrication techniques of microparticles vary a lot. Polymer microparticle production is typically done in two ways, first microfluidics-assisted techniques including droplet-based fabrication, flow-lithography-based fabrication, and microjetting; second other techniques including centrifugation, electrohydrodynamics, and molding. With a focus on microfluidics-assisted techniques, we bring a few remarkable and commercialized studies on high throughput production of spherical-shaped and irregular-shaped microparticles to your attention.

Spherical microparticles

Particle monodispersity has to be compromised for high-througput production when using coaxial microfluidic devices, and both features are highly desired in medical applications and industry. Luckily, as a droplet-based fabrication technique, high-throughput step emulsification of microparticles addresses this fundamental problem. David Weitz’s research group at Harvard University has recently reported a droplet generator microchip with 135 step-emulsifier nozzles that produce monodisperse emulsions of polymers at an exceptional throughput of 10K mL/h (Figure 1a).1 This means, monodisperse microparticle production with this device is thousands times higher than a typical droplet generator microchip with one droplet maker and a throughput of 10 mL/h. The chip is made of PDMS, which is a flexible and inexpensive material. Monodispersity  at high flow rates is maintained using microchannels connected through an array of parallelized nozzles (Figure 1b). Microparticles are formed at the step between each nozzle and the continuous-phase channel. The formation can be explained by the Laplace pressure difference developing between the nozzle and the symmetric polymer bulb, resulting in suction of the dispersed phase into the bulb. The growing polymer bulb increases the pressure gradient and a neck forms between the nozzle and the bulb due to depletion of dispersed phase, resulting in release of a droplet. This geometry can produce spherical-shaped microparticles. The production efficiency scales linearly with droplet diameter (Figure 1c). Weitz demonstrated the production of oil microcapsules in water with the envision of standardizing the process by converting the emulsifier into a pipettor tip. Such a technology can replace the existing pipettor technology tools including multi-well and robots, and this replacement can serve for parallelizing and automation of the encapsulation chemi- and bio-assays. This technology has recently been introduced to the market by a Switzerland-based startup company called Microcaps.

As an alternative concept, in-air microfluidics is based on the idea of producing droplets at higher flow rates without using microfluidic channels. In the research groups of Detlef Lohse and Marcel Karperien at University of Twente, microparticles were generated using two nozzles, and one of the nozzles is mounted on a vibrating piezoelectric element (Figure 1d). The breakup of the liquid jet ejected from the first nozzle leads to formation of monodisperse droplets, which hit onto a continuous liquid jet ejected from the second nozzle. After passing ‘the meeting point’, both liquids react with each other to form physically-encapsulated microparticles. This technique provides with hundreds to thousands times faster microparticle production when compared to coaxial microchip setups. Such constructs can be especially beneficial in tissue engineering, where rapid fabrication of multi-scale materials with multiple cell types is an ongoing challenge. This technology has recently been introduced to the market by a Dutch startup company called IamFluidics.

Figure 1. Up-scaled step-emulsification device producing monodisperse droplets. (a) A schematic of the entire microfluidic chip actively producing oil-in-water droplets. (b) The emulsification process. (c) Maximum production rates per nozzle plotted against drop diameter, scale bars are 400 µm.The image is modified from Stolovicki et al. (see the references below). (d) Chip-based microfluidics comparison with in-air microfluidics.

Irregular-shaped microparticles

Another microfluidics-assisted fabrication concept is stop-flow lithography, introduced by Patrick Doyle’s research group at Massachusetts Institute of Technology.2 In this concept, while two (or more) streams of monomers flow side by side through a microchannel made of PFPE coated PDMS, the streams are exposed to intermittent illumination of ultraviolet light through a photomask, which blocks the light selectively. Due to the chemical reaction initiated by ultraviolet light, the liquid solidifies, and forms an individual microparticle (Figure 2a). Upon polymerization, gel particles do not stick to the PFPE microchannel walls, allowing for the production of free-floating particles by the virtue of oxygen lubrication layers. As the ultraviolet light is projected onto the stream through the photomask, each particle takes on the shape of the mask, making the microparticles customizable (Figure 2b). Microparticles composed of multiple monomers can be fabricated by combining multiple monomer streams. The single-step production is advantageous to reduce the production costs, however the particle shape is limited by the photomask and the microchannel geometry – not allowing for generation of spherical-shaped particles. For a proof-of-concept demonstration, upconverting nanocrystal laden-microparticles were synthesized and emitted homogenous visible spectrum of light. The technique allows for synthesis of striped microparticles without losing their homogeneous emission property. The microparticles were also encoded with multiple dot-patterns (Figure 2c), each specific to a target molecule (such as DNA) reacting with the other ingredients in the particle. Such a reaction leads to the formation of a fluorescent color in the microparticle, so the reaction can be traced by microscopy. This technology has been introduced to the market by Firefly Bioworks (acquired by Abcam in 2015), and Motif Micro (acquired by YPB Systems in 2018) startup companies.

microparticles

Figure 2. Stop Flow Lithography concept. (a) A schematic demonstration the coaxial microchip. (b) Bright-field and fluorescent images show triangle-shaped particles (c) A mask with an array of barcode particle shapes was aligned on three phase laminar flows in the microchip. Bright-field and fluorescent images show the barcoded particles with three distinct compartments with a region coding “2013”. The image is modified from Bong et al. (see the references below).

To download the full articles click the links below:

1Throughput enhancement of parallel step emulsifier devices by shear-free and efficient nozzle clearance
Elad Stolovicki, Roy Ziblat, and David A. Weitz
Lab Chip, 2018.
DOI: 10.1039/C7LC01037K

2Stop flow lithography in perfluoropolyether (PFPE) microfluidic channels
W. Bong, J. Lee, and P. S. Doyle
Lab Chip, 2014.
DOI: 10.1039/C4LC00877D

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for single-cell analysis, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Why should we use optofluidics for monitoring marine environment?

Phosphorus is found in natural waters and exerts a major influence on the composition and structure of aquatic ecosystems. It is a crucial nutrient for planktons and algae, which feed fish and other marine organisms. However, human activities may result in excess amount of phosphorus, which, in turn, causes harmful algae to bloom in natural waters. The bloom creates a hostile environment to other forms of marine life by consuming the available oxygen in the sea, and producing toxins. Sea organisms such as fish swim away from the blooms, but the ones that cannot swim, such as shellfish, unfortunately die. We do care about this occurrence as it negatively affects natural life and the economy. There is only one way to interpret the effect of continuously changing phosphorus levels on the strength of the biological pump: real-time monitoring of phosphate levels in the marine environment!

Figure 1. The design of the Fabry-Pérot microcavity, consisting of two parallel mirrors (reflectors) fabricated by coating the surface of the optical fibers with a gold layer. The light is reflected by the mirrors multiple times to enhance the signal. Adapted from Zhu et al., 2017.

Conventional vs. optofluidic monitoring instruments

Conventional phosphate monitoring instruments are mostly used for on-site sampling, then the fresh sample is transported to a laboratory for determining the phosphate level. Laboratories complete one round of analysis in 20 min, often using spectrophotometrical measurement tools. Given the conditions, real-time phosphate monitoring easily becomes laborious, time consuming, and costly. To address this challenge, researchers in Chinese Academy of Sciences, Wuhan University, and The First Institute of Oceanography in China collaborated to develop a portable optofluidic phosphate monitoring tool. However, prototyping an optofluidic marine phosphate detection tool is not straightforward because an absorption cell—a component core to the measurement unit—is simply too big to fit in a microchip. Instead of using a bulky absorption cell, researchers considered integrating a Fabry-Pérot cavity in the microsystem. The Fabry-Pérot cavity consists of two parallel optical fibers with a spacing in between. The cross-sectional surface of each optical fiber is coated with a thin layer of gold to create reflector surfaces (Figure 1) in order to enhance the absorption of phosphate. Shortening the spacing between the reflectors decreases the analysis time from minutes to seconds.

 

How it works?

In the microchip, filtered water sample and a chromogenic reagent are injected into a curved microchannel. After the chromogenic reaction, the water-soluble components are transported into the optical section (Figure 2). The probe light is sent into the Fabry-Pérot cavity via one of the fibers, bounces between the reflectors multiple times to increase the optical feedback and then analyzed by the detector. The obtained absorbance value, therefore, increases linearly with increasing phosphate concentration. In this microsystem, phosphate detection range is 0.1-100 µmol per liter (400 times greater than the range of a conventional instrument) and detection time is 4 seconds (300 times shorter than detection time of a conventional instrument). The authors of the paper think that this technology can be applied to detect other nutrient levels as well as pH changes in marine environment.

 

optofluidic phosphate monitoring

Figure 2. A schematic of the optofluidic microchip consisting of two parts: the microfluidics circuit forming the microreactor in the microchannel, and the optical part to provide optical feedback for enhanced absorption analysis. Adapted from Zhu et al., 2017.

To download the full article for free* click the link below:

 

Optofluidic marine phosphate detection with enhanced absorption using a Fabry–Pérot resonator

M. Zhu, Y. Shi, X. Q. Zhu, Y. Yang, F. H. Jiang, C. J. Sun, W. H. Zhaoc, and X. T. Hanc

Lab Chip, 2017, Lab on a Chip Recent Hot Articles

DOI: 10.1039/C7LC01016H

 

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

*until 16th February 2018

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Spotting cancer: one in a billion cells

The human body consists of tens of trillions cells, all of which theoretically should have the same genome. Depending on genetic and environmental factors, some of these cells experience point mutations. Although most of those mutations are cleaned up by DNA repair enzymes, about 0.01% of them stay. A low percentage of the persistent mutations turn out to be ‘cancer’ while others stay recessive. Several genes, including the ones responsible for cell growth cycle, cause the persistent mutations. Uncontrolled growth of cells leads to formation of tumor, which is now prone to experience more mutations due to continuous proliferation. These mutations create heterogeneity among the cell population of a tumor, and eventually some cells leave their original tumor and start a new one in another organ of the body. When a cell leaves its parent tumor, it starts circulating in blood vessels before settling in. Those cells are called circulating tumor cells (CTCs), and around 1-10 CTC can be found in 1 mL of blood (which contains about 1 billion red blood cells, and 1 million white blood cells). Capturing ultra-rare CTCs has enormous implications in early cancer diagnosis. Often times, analysis of at least 10 mL of blood is necessary to capture sufficient CTCs to confirm their presence. The available technology can achieve CTC capturing in about 10 hours leading to the loss of target cells and decay of detection biomarkers.

Microfluidic devices are well known for precise sorting of microscale materials. Parallelizing microscale sorting in microfluidic devices enables high-throughput sample processing. In the light of this principle, David Issadore, Jina Ko, and their fellow researchers at University of Pennsylvania coined CaTCh FISH, a circulating tumor cell fluorescence in situ hybridization platform for rapid detection of CTCs. David Issadore kindly accepted to talk about this exciting lab-on-a-chip device. According to David, “the main strength of the CaTCh FISH is that it preserves the sensitivity and specificity of microfluidic cell sorting and RNA FISH, but through clever engineering allows these normally very slow laboratory-based operations to be performed rapidly and automatically on a chip.”

RNA FISH, high-throughput cell handling

Figure 1. Overview of the CaTCh FISH platform. Whole blood sample is processed in TEMPO step, where magnetic nano particle based cell separation is followed by single-cell RNA analysis (modified from Ko et al., 2017).

Processing a whole blood sample using CaTCh FISH involves three steps (Figure 1). First, white blood cells are labelled with magnetic nanoparticles. Second, whole blood is passed through a magnetic micropore filter to selectively trap magnetically labelled cells. “Our magnetic micropore device rapidly and precisely removes all of the cells that we know are not CTCs”, says David. The operating principle of magnetic micropore filter is based on strong and highly localized microscale field gradients formed at the edge of micropores to enable application of high flow rates. Third, single cell RNA analysis is performed on isolated cells using rapid in-situ hybridization strategy so that CTCs can be identified within the isolated cell population. In this way, targeted CTCs can be isolated from the rest of the cell population regardless of their physical and molecular properties. Analysis of a 10 mL blood sample takes less than an hour.

As a key novelty, the researchers maintained high-throughput processing and high sensitivity at the same time by integrating the FISH technique (hybridization of 20-50 fluorescently-labelled oligonucleotide probes to the target RNA, and subsequent fluorescence-signal based detection to enhance signal-to-noise ratio) in a microfluidic chip. CaTCh FISH has also been tested in patients with pancreatic cancer and detected CTCs in the real patient samples.

“The CaTCH FISH technology can be easily modified to measure other rare cells, for the diagnosis of other cancers or for stem cell research for example, by modifying the RNA FISH probes”, says David. He considers converting the platform to a high-precision hospital-based diagnostic tool and he collaborates with a company in the Bay area for this process. The CaTCh FISH device is poised to have a big impact on the way cancer is diagnosed.

To download the full article for free* click the link below:

A magnetic micropore chip for rapid (<1 hour) unbiased circulating tumor cell isolation and in situ RNA analysis

Jina Ko, Neha Bhagwat, Stephanie S. Yee, Taylor Black, Colleen Redlinger, Janae Romeo, Mark O’Hara, Arjun Raj, Erica L. Carpenter, Ben Z. Stanger and David Issadore

Lab Chip, 2017, Paper

DOI: 10.1039/C7LC00703E

 

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

*until 5th January 2018

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Zenith in “artery”

When cutting a finger, thrombocytes and fibrin in the blood make up the blood-clotting mechanism, aka. haemostasis, to stop the blood loss. Another way to trigger this mechanism is having an artery damaged by atherosclerosis, which is often caused by several genetic or acquired factors. In the latter case, thrombosis develops within a vein or artery, obstructing or stopping the blood flow to major organs like the heart and eventually causing heart attack. Considering every year over 14 million lives worldwide are lost to heart attacks, more investigation on this topic is needed without any doubt.

Recently, a research team led by Andries van der Meer published a research article in Lab on a Chip on mimicking arterial thrombosis in 3D vascular structures, representing a major step forward in the development of accurate and faster methods of studying arterial thrombosis without using animals. The authors highlighted the inconvenience of using animal models to predict arterial thrombosis in humans. This is mainly due to fundamental differences between human and animal physiology, the researchers explain. For instance, rodent platelet biology, coagulation dynamics, and shear stress in mice arteries significantly vary between humans and mice.

thrombosis on chip

Figure 1. Three-dimensional models of a healthy and stenotic vessels and thrombosis formation upon blood perfusion through the channels.

The paper uses miniaturized vascular structures mimicking 3D architectures found in both healthy and stenotic blood vessels in-vitro (Figure 1). They combined stereolithography and 3D printing of computed tomography angiography data to construct 3D-printed templates of vessels in PDMS microchips. The 3D printed vessels are then coated with human umbilical vein endothelial cells, forming a monolayer fully covering the surface. In the next step, the artificial vessels are perfused with blood at normal arterial shear rates, allowing a blood clot to form as it would happen in the human body. The 3D printed vessel is clinically more relevant when compared to 2D vessel models, since the realistic flow profiles of blood and even distribution of shear stress across the vessel are of great importance when researching arterial thrombosis. Hugo Albers, the co-first author of the paper explains what led the team to try 3D models: “Other groups have worked on thrombosis-on-a-chip before, but we wanted to incorporate flow profiles that are similar to what one would find in-vivo. So we opt for a round and thus 3D shape. Since the stenotic geometry is an important part of this work, we wanted to find a technique that allowed us to make almost any shape we could come up with. Thus 3D-printing seemed to be the way to go.”

When it comes to defining the challenges in 3D organ-on-chip modeling and fabrication, “we needed to replicate the cellular environment using human endothelial cells and human whole blood to fully mimic the nature of vasculature” says Albers. “Incorporating the shape of vasculature to recreate the flow profiles found in-vivo and recreating the shape of vasculature on a small scale was quite challenging, since the resolution of 3D-printing quickly started to be the limiting factor. Furthermore, we ran into problems related to working with whole blood. We had to figure out how to perfuse small channels with blood without instigating thrombosis outside of the microfluidic channel.” The researchers successfully overcame the challenges mentioned by Albers and mimicked the formation of thrombosis in a stenotic vessel model as seen in Figure 1 (bottom).

The researchers note that the next step involves co-culturing arterial endothelial cells and smooth muscle cells with human umbilical vein endothelial cells or moving to different cell lines such as differentiated human induced pluripotent stem cells. “I think we can also apply the 3D-printing technique to create thrombosis-on-a-chip devices with different geometries, e.g. aneurysms or bifurcated geometries”, says Albers.

To download the full article for free* click the link below:

Mimicking arterial thrombosis in a 3D-printed microfluidic in vitro vascular model based on computed tomography angiography data

Pedro F. Costa, Hugo J. Albers, John E. A. Linssen, Heleen H. T. Middelkamp, Linda van der Hout, Robert Passier, Albert van den Berg, Jos Malda and Andries D. van der Meer

Lab Chip, 2017, Paper

DOI: 10.1039/C7LC00202E

This paper is included in our Organ-, Body- and Disease-on-a-Chip Thematic Collection. To read other articles in the collection, visit – rsc.li/organonachip

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

How can biosensors provide real-time health monitoring?

Like a ripple spreading outwards on a pond’s surface, a plasmon is a collective oscillation of free electrons in a piece of metal. When the metal interacts with light (in this case k vector of light satisfies the momentum condition), the collective movement of oscillating electrons at the metal’s surface leads to the propagation of the light along the surface, also known as a surface plasmon. This simple physics rule is very helpful for sensor nanotechnology and optical signal processing applications since the offered advantages are significant, providing a smaller foot-print, lower limits of detection, and multiplexing opportunities. However, using sensors for biomolecule detection requires clever use of light. For example, surface plasmon resonance can be observed in nanohole arrays patterned on very thin gold films. Nanohole arrays can transmit light much more strongly than expected for the nanohole apertures at certain wavelengths. This phenomenon is called extraordinary optical transmission (EOT) and opens a new avenue for detection of minute amounts of biomolecules.

A nanoplasmonic biosensor was recently developed for real-time monitoring of proteins from live cells in a label-free configuration, thanks to extraordinary optical transmission. The biosensor is structured in a microfluidic device consisting of a cell module and the biosensor module. Microfluidic cell module design is based on a single zigzag channel for directly delivering the secreted proteins to the adjacent biosensor module via a tubing connection. The biosensor module consists of nanoholes fabricated on freestanding SiNx membranes. Antibodies specific to vascular endothelial growth factor (VEGF) are selectively immobilized on the gold nanohole arrays as biorecognition molecules. When the VEGF are captured on the sensor, a change of refractive index proximate to the surface is induced. This change results in a peak shift of the EOT spectrum (Figure 1). By tracing the spectral shifts continuously, the dynamics of cell secretion can be monitored. In this way, the secretion dynamics from live cancer cells are monitored and quantified for 10 hours. The proposed microfluidic device has unique capabilities for multiplexed and label-free detection in a compact footprint, which are promising for miniaturization and integration into lab-on-a-chip devices.

biosensor, microfluidics, extraordinary transmission phenomena, nanohole arrays

Design and working principle of microfluidic-integrated biosensor. Cancer cells grow in a zigzag channel, and secreted vascular endothelial growth factor are directly delivered to the adjacent detection module. Nanohole structures fabricated in the detection (biosensor) module are shown in SEM image with a scale bar of 1 μm (bottom left). The images on the right show the characteristic resonance peak (solid line) and EOT spectral shift of the peak upon binding (dashed line). Spectral displacements of the resonance peak based on molecular binding accumulation is shown in the sensorgram to reveal the real-time binding dynamics. Adapted from Li et al. (Lab Chip, 2017).

This technology will have a potentially significant impact on medicine. Most of the patients agree that preventive medicine is preferable to reactive medicine. However, preventive medicine requires frequent physical exams, which can only be maintained by spending substantial time and money at physicians’ offices. The need for frequent check-up exams could be reduced or eliminated by real-time monitoring of the health status by portable biosensors in the future. Developing biosensors that allow real-time monitoring of target biomolecules is a big step towards the addressing this future goal.

 

To download the full article for free* click the link below:

Plasmonic nanohole array biosensor for label-free and real-time analysis of live cell secretion

Xiaokang Li, Maria Soler, Cenk I. Özdemir, Alexander Belushkin, Filiz Yesilköy and Hatice Altug

Lab Chip, 2017

DOI: 10.1039/C7LC00277G

 

*Free to access until 7th August 2017.


About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in Herr Lab at UC Berkeley in the United States. Her research interests include development of microfluidic devices for quantitative analysis of proteins from single-cells, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

The future of bioensors

St. Paul’s Cathedral in London has its own unique acoustics. The architecture of the dome allows a whisper to be heard from anywhere within the circular gallery, so-called the whispering gallery. The invention of whispering-gallery-mode (WGM) biosensors is indeed derived by this special gallery in St. Paul’s: just like a sound wave travelling within the dome, a light beam traveling within a glass sphere (in this case, a biosensor) circles multiple paths so that any molecule on the surface can be detected. Thanks to this powerful technique, interactions of unlabeled molecules can be analyzed with high sensitivity in real-time.

In early March of 2017, researchers from Max Planck Institute and University of Exeter published a comprehensive review paper in Lab on a Chip, explaining the advances of WGM sensors as scientific laboratory instruments, their development into lab on a chip devices, major challenges on the way towards real-world applications, and potential future applications.

WGM sensors probe the interaction between molecules and electromagnetic waves during a biomolecular reaction, and convert this information to a measurable signal. The probing is made possible thanks to the electromagnetic modes formed inside a resonator with axial symmetry. However, the electromagnetic waves slightly extend into the surrounding medium. Any changes in the surrounding medium, and therefore in the evanescent field, cause a shift of the resonance frequency—this is the basis of the sensing mechanism. WGMs are capable of sensing this shift in three ways: (1) Resonance frequency shift based sensing: measurable signal is the magnitude of the frequency shift, and the sensitivity of the sensor, which scale with the evanescent field strength at the distortion’s position, i.e. interaction of a single atomic ion with a plasmonic nanoparticle (Figure 1a). (2) Loss based sensing: it is based on the resonator’s energy loss per light wave oscillation, i.e. binding of polystyrene nanoparticles (Figure 1b). (3) Mode-splitting based sensing: a scattering molecule/particle couples clock-wise and counter clock-wise propagating WGMs, resulting in the formation of two different standing wave modes, i.e. deposition of multiple nanoparticles on a surface (Figure 1c).

Whishering gallery mode biosensors

Figure 1. Three different sensing mechanisms of whispering-gallery-mode biosensors. (a) Resonance frequency shift based sensing, (b) loss based sensing, (c) mode-splitting based sensing (from Kim et al., Lab Chip, 2017).

The review also focuses on several performance criteria of WGM sensors, such as single molecule sensitivity, time resolution, stability and specificity. Single molecule sensitivity of WGM sensors depends on the resonator’s size, the surrounding medium and excitation wavelength. Despite the fact that these parameters seem to limit the sensitivity, increasing the electric field inside a nanoscale volume significantly can circumvent this problem. Apart from that, WGM sensors can detect events happening in milliseconds to seconds whereas these detection speeds are mostly limited by the equipment, for example, the laser’s maximum scanning speed. When it comes to stability of WGM sensors, one common problem is reported to be the environmental noise sources, affecting the reliability of the measurements. A variety of methods to reduce those negative effects are further discussed in the review. One another notable functionality is that WGM sensors can be as specific as probing a surface-immobilized receptor molecule reacting with an analyte of interest.

microring resonator based on-chip sensor, pillar-supported high Q cavities

Figure 2. Lab on a chip WGMs. Left and middle images show a microring resonator based on-chip sensor with zoom-in images of different components, and right image shows a pillar-supported high Q cavities (from Kim et al., Lab Chip, 2017).

Lab on a chip applications of WGMs are discussed in two categories in the review (Figure 2): Planar resonators let the light to be coupled into multiple ring-resonators that are connected to channels containing different analytes. This type of resonators is low-cost and allows for in-parallel probing of samples. Pillar-supported high Q cavities is the second type, featuring a high Q factor owing to the air-gap between the substrate and the cavities. Pillar-supported resonators are high-cost due to several fabrication difficulties. Apart from those, droplet-based in vivo sensing via WGM sensors is also addressed as an alternative approach with the possibility of using the analyte medium itself as a resonator. Over the past decade, WGM sensors have been widely exploited to study molecular interactions with high sensitivity and seem to gain more and more attention.

 

To download the full article for free* click the link below:

Towards next-generation label-free biosensors: recent advances in whispering gallery mode sensors

Eugene Kim, Martin D. Baaske and Frank Vollmer

Lab Chip, 2017, Critical Review

DOI: 10.1039/C6LC01595F

*Free to access until 12th July 2017.

 

About the Webwriter

Burcu Gumuscu is a postdoctoral fellow in BIOS Lab on a Chip Group at University of Twente in The Netherlands. Her research interests include development of microfluidic devices for quantitative analysis of proteins of a single-cell, next generation sequencing, compartmentalized organ-on-chip studies, and desalination of water on the microscale.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)