Lab on a Chip Blog

For the first time, refractive index sensitivity comparable to that of a commercial surface plasmon resonance sensor has been achieved in a nanohole array-based system, thanks to a team of Canadian engineers.

Surface plasmon resonance (SPR) sensors rely on the optical properties of thin gold films in order to measure changes in refractive index.  SPR has been long been utilized for label-free biosensing, in which target molecules binding to a capture layer cause minute refractive index changes.¹  Traditionally, these changes are measured via the reflectance spectrum of the gold film, requiring the light source and the detector to be placed at specific angles to the sample.  This arrangement limits the types of experiments that can be carried out.  However, if a gold film perforated with nanoholes is used, refractive index changes can be measured via the transmittance spectrum², allowing the light source and detector to be arranged along a single light path, as in an ordinary spectrometer. 

Prof. Reuven Gordon led a collaboration between the University of Victoria, the University of Ottawa, and Carleton University in an effort to improve the refractive index sensitivity of these nanohole array-based systems. The team made three key innovations:  creating an ultra-smooth gold surface via template stripping, optimizing the shape of the nanoholes, and designing a support using a transparent material with a refraction index close to that of water.  With these improvements, the researchers were able to match the sensitivity of commercial SPR systems using simple optical instrumentation.  Because the nanohole substrates are used in a transmission geometry, they can be incorporated into optical and microfluidic systems in which SPR sensing has previously been unfeasible.

The image adapted from Figures 2b and 6a shows (a) the nanohole array and (b) its transmission spectra in various solutions.

References:

1.     C. Boozer et al., Current Opinion in Biotechnology 2006, 17(4), 400–405, .
2.     A. Krishnan et al., Optics Communications 2001, 200, 1–7, .

Read more in this HOT article from Lab on a Chip!

Atomically flat symmetric elliptical nanohole arrays in a gold film for ultrasensitive refractive index sensing
Gabriela Andrea Cervantes Tellez, Sa’ad Hassan, R. Niall Tait, Pierre Berini and Reuven Gordon
DOI: 10.1039/C3LC41411F

View the very best research in miniaturization from Canada in our themed issue Focus on Canada!

Katie Mayer is a post-doctoral researcher in the Walt Laboratory at Tufts University, USA

Researchers at the City University of Hong Kong and Jinan University, China, have developed a rapid approach to study how cells “feel” the forces around them.

Cells sense and react to their physical surroundings through mechanotransduction—the translation of mechanical stimulation into biochemical signals. These signals, in turn, regulate many important physiological processes such as those in the immune system, bone metabolism and blood circulation. Since defects in mechanotransduction are associated with various human diseases,¹ understanding their molecular basis may aid in the development of new therapeutics. Unfortunately, most techniques for studying mechanotransduction are slow and labour-intensive, requiring meticulous manipulation of single cells for mechanical stimulation and analysis.

To address this challenge, a research team led by Prof. Mengsu Yang has developed a new microfluidic chip that can isolate individual cells and apply precise whole-cell mechanical stimulation.

The microfluidic chip is assembled by sandwiching a deflectable polymer membrane between a fluid layer and a control layer. The chip comprises three parallel channels, two microvalves and one compressive component in the middle channel (see picture). By modulating the pressure in the control channels, the height of the middle channel can be adjusted to trap or compress an individual cell from a suspension. The microvalves can be opened or closed to exchange the reagent environment surrounding the trapped cell.

Using this chip, the research team studied the intracellular calcium signaling in HL60 cells (leukemic cells) triggered by whole-cell compression. They demonstrate that mechanical compression can activate ion channels in the cell membrane, causing extracellular calcium ions to transport inside the cell. Interestingly, they show that an intact cytoskeleton was not required for the activation of mechanosensitive ion channels in HL60 cells—the involvement of the cytoskeleton in mechnotranduction remains a much-debated topic in the field.

Taken together, the research team successfully demonstrated that this microfluidic chip is a fast, useful platform for the study of mechanotransduction in individual suspension cells. In the future, the throughput of this chip may be extended by parallelizing several compressive components on one chip.

1.            Jaalouk, D. E.; Lammerding, J. Nature Reviews Molecular Cell Biology 2009, 10, 63-73.

Microfluidics study of intracellular calcium response to mechanical stimulation on single suspension cells
Tao Xu, Wanqing Yue, Cheuk-Wing Li,  Xinsheng Yao and Mengsu Yang
DOI: 10.1039/C3LC40880A

Alphonsus Ng is a PhD student in the Wheeler Microfluidics Laboratory, University of Toronto, Canada

Researchers at the University of Canterbury in New Zealand have created a platform measuring mechancial forces exerted by the microscopic worm C. elegans in locomotion. The platform can measure all of the important worm locomotion parameters in a single assay. The team has noted that the worm’s crawling behaviors and thrust forces correlate to the structure of their microenvironment as the worm adjusts its behavior via mechanical sensing of its surroundings.

C. elegans are soil-dwelling worms made up of just 959 cells (adult hermaphrodite). The worms are 1 mm long and 80 μm in body diameter. In labs studying C. elegans, the worms crawl on agar plates in search of food (usually E. coli) by twisting their body in sinusoidal waves.¹ The sense of touch is crucial to these nematodes: 6 touch receptor neurons (mechanoreceptor neurons) allow the animal to detect external mechanical feedback with the environment as well as internal forces.²

The group led by Maan M. Alkaisi of The MacDiarmid Institute, New Zealand, and Wenhui Wang now at Tsinghua University, China, developed micropillar arrays of various arrangements and dimensions to modify the worm’s microenvironment and measure forces exerted by the worm as it crawls on the substrate. The researchers were also able to quantify locomotion parameters such as speed, amplitude of sine wave, and wavelength. Their unique assay combines 3 key elements: variable substrate topology, worm thrust force measurements, and locomotive metrics. One version of the device is also compatible with different substrates by mounting pillars on top of migrating worms instead of allowing worms to migrate directly on the microstructures.

The group found that reduced pillar spacing caused wild-type worms to exert twice the force to crawl through the substrate, especially in a honeycomb pillar arrangement. The worms were also much slower at moving in the narrow pillar structures and the frequency of sine wave propagations correlated to resistivity of the physical environment. The platform presented in this study enables many exciting studies in C. elegans locomotion and touch response, especially as  many genetic mutant strains are available with changes to the number of mechanoreceptor neurons and muscle arms. ³

References:

1. S. Berri, J. H. Boyle, M. Tassieri, I. A. Hope and N. Cohen, HFSP journal, 2009, 3, 186-193.
2. M. B. Goodman, in WormBook: the online review of C. elegans biology, NIH Public Access, 2006, available from http://www.ncbi.nlm.nih.gov/books/NBK20187/.http://www.wormbook.org/chapters/www_mechanosensation/mechanosensation.html.
3. C. I. Bargmann and I. Mori, in C. elegans II. 2nd edition., ed. D. L. Riddle, T. Blumenthal, B. J. Meyer and J. R. Priess, Cold Spring Harbor Laboratory Press, NY, 1997, available from http://www.ncbi.nlm.nih.gov/books/NBK20187/.

On-chip analysis of C. elegans muscular forces and locomotion patterns in microstructured environments
Shazlina Johari, Volker Nock, Maan M. Alkaisi, and Wenhui Wang. Lab Chip, 2013, 13, 1699-1707.
DOI: 10.1039/c3lc41403e

Sasha is a PhD student at Stanford University working with Professor Beth Pruitt’s Microsystems Lab. Her research interests focus on designing microscale devices for studying cell mechanobiology and the biophysical underpinnings of cell-cell and cell-substrate interactions.

 These articles are HOT as recommended by the referees. And we’ve made them free to access for 4 weeks*

A Microfluidic Platform for Evaporation-based Salt Screening of Pharmaceutical Parent compounds
Sachit Goyal, Michael R. Thorson, Cassandra L. Schneider, Geoff G. Z. Zhang, Yuchuan Gong and Paul J. A. Kenis  
DOI: 10.1039/C3LC41271G

Atomically flat symmetric elliptical nanohole arrays in a gold film for ultrasensitive refractive index sensing
Gabriela Andrea Cervantes Tellez, Sa’ad Hassan, R. Niall Tait, Pierre Berini and Reuven Gordon  
DOI: 10.1039/C3LC41411F

SAW-controlled drop size for flow focusing
Lothar Schmid and Thomas Franke
DOI: 10.1039/C3LC41233D

On-chip analysis of C. elegans muscular forces and locomotion patterns in microstructured environments
Shazlina Johari, Volker Nock, Maan M. Alkaisi and Wenhui Wang
DOI: 10.1039/C3LC41403E

Aquifer-on-a-Chip: understanding pore-scale salt precipitation dynamics during CO2 sequestration
Myeongsub Kim, Andrew Sell and David Sinton 
DOI: 10.1039/C3LC00031A

This article is featured in the collection Lab on a Chip Top 10%

Site-specific peptide and protein immobilization on surface plasmon resonance chips via strain-promoted cycloaddition
Angelique E. M. Wammes, Marcel J. E. Fischer, Nico J. de Mol, Mark B. van Eldijk, Floris P. J. T. Rutjes, Jan C. M. van Hest and Floris L. van Delft   Shazlina Johari, Volker Nock, Maan M. Alkaisi and Wenhui Wang
DOI: 10.1039/C3LC41338A

Microfluidic LC device with orthogonal sample extraction for on-chip MALDI-MS detection
Iulia M. Lazar and Jarod L. Kabulski
DOI: 10.1039/C3LC50190F

Digital microfluidics-enabled single-molecule detection by printing and sealing single magnetic beads in femtoliter droplets
Daan Witters, Karel Knez, Frederik Ceyssens, Robert Puers and Jeroen Lammertyn  
DOI: 10.1039/C3LC50119A

Control of neural network patterning using collagen gel photothermal etching
Aoi Odawara, Masao Gotoh and Ikuro Suzuki
DOI: 10.1039/C3LC00036B

Microfluidic large scale integration of viral–host interaction analysis
Ya’ara Ben-Ari, Yair Glick, Sarit Kipper, Nika Schwartz, Dorit Avrahami, Efrat Barbiro-Michaely and Doron Gerber  
DOI: 10.1039/C3LC00034F

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Professor Noo Li Jeon and co-workers from Seoul National University have published an important paper in Lab on a Chip about creating vascular networks in microfluidic devices. The networks are so well-developed that they can even be flushed with fluids and cells.

In the paper, the researchers describe a new method to culture endothelial cells in a microfluidic, three-dimensional environment. The endothelial cells form a network of microvessels within a few days. The researchers show that by adding other cell types to the culture, the network can be used to study specific interactions of vessels with connective tissue, tumor tissue and blood. The endothelial network is so mature that it can be flushed with medium without leakage and that the endothelial cells respond to the mechanical forces that result from the fluid flowing over their surface.

The perfusion is nicely illustrated in this movie from the paper, showing microbeads flowing from one side of the network (top) to the other (bottom).

Additionally, the devices give a lot of structural information about the microvessels, as can be seen in the above picture from the article. It shows an endothelial network in a microfluidic device, with fluorescent labels for cell nuclei, cytoskeletal actin fibers and the cell-cell adhesion molecule CD31. The network displays a branching morphology with clearly delineated vessels and high integrity.

Taken together, this is probably the most realistic laboratory model of the microvasculature to date. The versatility of the model is demonstrated by the extensive characterization of cell-cell interactions and the functional responses of endothelial cells to flow. The realism of the model, together with a high degree of control over many important cell culture parameters makes this model superior to many current laboratory models of microvascular networks.

In the future, these types of models will be useful for studying pathological blood vessel formation, for example by systematically changing the cell culture environment or by using patient-derived cells.

Engineering of functional, perfusable 3D microvascular networks on a chip
Sudong Kim, Hyunjae Lee, Minhwan Chunga and Noo Li Jeon
DOI: 10.1039/C3LC41320A

This article is from the themed collection Lab on a Chip Top 10%

Andries van der Meer, PhD, is a post-doctoral fellow at the Wyss Institute for Biologically Inspired Engineering, Harvard University, USA.