Lab on a Chip Blog

Researchers at the University of California, Los Angeles have developed a method to rapidly quantify the mechanical properties of single cells at high resolution using hydrodynamic and inertial fluid focusing. 

Cells undergo structural changes during disease states, particularly in certain cancer cell lines. For example, tumor cells with increased invasive potential exhibit increased deformability, which aids them during their migration into surrounding tissues¹. Measuring the mechanical properties of single cells as a biomarker of cell health using conventional Atomic Force Microscopy (AFM) or micropipette aspiration is time-consuming and requires extensive sample prep, limiting the analysis to a few cells. Dino Di Carlo’s group and collaborators developed a way to apply fluids to stretch single cells along two axes using hydrodynamic flow and perpendicular cross-flows without waiting for cells to stop within the channel. This method, termed ‘hydropipetting’, is compatible with inline microfluidic rinsing, capable of processing 65000 cells/sec, and utilizes automatic image processing to rapidly derive the mechanical phenotype of cell populations. 

Hydropipetting starts with inertial fluid focusing of cells to position them precisely in a flow channel by balancing lift forces and secondary flows by fine control over the Reynolds number of the fluid. Cell-free liquid is then excluded and cells are deformed both parallel and perpendicular to the main channel flow. Automated image data analysis then extracts metrics of cell strain, viscosity, diameter and deformability from high speed observation during cell deformation. 

Di Carlo and his group demonstrated the hydropipetting technique on two cancer cell lines (HeLa and Jurkat cells) and observed increases in cell deformability upon drug treatment to increase invasiveness, metastatic potential, and when disrupting structural cellular filaments. 

References:
[1] S. E. Cross, Y. Jin, J. Rao and J. K. Gimzewski, Nature Nanotechnology, 2007, 2, 780-783. 

Pinched-flow hydrodynamic stretching of single-cells
Jaideep S. Dudani, Daniel R. Gossett, Henry T. K. Tse and Dino Di Carlo. Lab Chip, 2013, 13, 3728-3734.
DOI: 10.1039/C3LC50649E

These HOT articles were recommended by our referees and are free to access for 4 weeks*

A portable explosive detector based on fluorescence quenching of pyrene deposited on coloured wax-printed μPADs
Regina Verena Taudte, Alison Beavis, Linzi Wilson-Wilde, Claude Roux, Philip Doble and Lucas Blanes  
DOI: 10.1039/C3LC50609F

Capillarics: pre-programmed, self-powered microfluidic circuits built from capillary elements
Roozbeh Safavieha and David Juncker  
DOI: 10.1039/C3LC50691F

Detection of real-time dynamics of drug–target interactions by ultralong nanowalls
Andreas Menzel, Raphael J. Gübeli, Firat Güder, Wilfried Weber and Margit Zachariasa  
DOI: 10.1039/C3LC50694K

Ultrasensitive microfluidic solid-phase ELISA using an actuatable microwell-patterned PDMS chip
Tanyu Wang, Mohan Zhang, Dakota D. Dreher and Yong Zeng  
DOI: 10.1039/C3LC50783A

Protein–DNA force assay in a microfluidic format
Marcus Otten, Philip Wolf  and Hermann E. Gaub  
DOI: 10.1039/C3LC50830G

A microfluidic device for dry sample preservation in remote settings
Stefano Begolo, Feng Shen and Rustem F. Ismagilov  
DOI: 10.1039/C3LC50747E

Application of [18F]FDG in radiolabeling reactions using microfluidic technology
Vincent R. Bouveta and Frank Wuest  
DOI: 10.1039/C3LC50797A

Size-selective collection of circulating tumor cells using Vortex technology
Elodie Sollier, Derek E. Go, James Che, Daniel R. Gossett, Sean O’Byrne, Westbrook M. Weaver, Nicolas Kummer,Matthew Rettig, Jonathan Goldman, Nicholas Nickols, Susan McCloskey, Rajan P. Kulkarni and Dino Di Carlo 
DOI: 10.1039/C3LC50689D

Ratcheted electrophoresis for rapid particle transport
Aaron M. Drews, Hee-Young Lee and Kyle J. M. Bishop  
DOI: 10.1039/C3LC50849H

Parallel measurements of reaction kinetics using ultralow-volumes
Etienne Fradet, Paul Abbyad, Marten H. Vos and Charles N. Baroud  
DOI: 10.1039/C3LC50768H

Controlling thread formation during tipstreaming through an active feedback control loop
Todd M. Moyle, Lynn M. Walker and Shelley L. Anna  
DOI: 10.1039/C3LC50946J

Micro magnetofluidics: droplet manipulation of double emulsions based on paramagnetic ionic liquids
Viktor Misuk, Andreas Mai, Konstantinos Giannopoulos, Falah Alobaid, Bernd Epple and Holger Loewe  
DOI: 10.1039/C3LC50897H

A microfluidic approach to synthesizing high-performance microfibers with tunable anhydrous proton conductivity Mohammad Mahdi Hasani-Sadrabadi,  Jules J. VanDersarl, Erfan Dashtimoghadam, Ghasem Bahlakeh, Fatemeh Sadat Majedi, Nassir Mokarram, Arnaud Bertsch, Karl I. Jacob and Philippe Renaud  
DOI: 10.1039/C3LC50862E

One-step microfluidic generation of pre-hatching embryo-like core–shell microcapsules for miniaturized 3D culture of pluripotent stem cells
Pranay Agarwal, Shuting Zhao, Peter Bielecki, Wei Rao, Jung Kyu Choi, Yi Zhao, Jianhua Yu, Wujie Zhang and Xiaoming He  
DOI: 10.1039/C3LC50678A

High-throughput metabolic genotoxicity screening with a fluidic microwell chip and electrochemiluminescence
Dhanuka P. Wasalathanthri, Spundana Malla, Itti Bist, Chi K. Tang, Ronaldo C. Fariaa and James F. Rusling  
DOI: 10.1039/C3LC50698C

*Free access to individuals is provided through an RSC Publishing personal account. It’s quick, simple and more importantly – free – to register!

New research shows that it is possible to carry out flow switching in microfluidic devices via a single active hardware element: a tunable frequency periodic pressure source.

A common hindrance to the design of microfluidic systems is the large amount of unwieldy and expensive hardware (valves, actuators, etc.) required to control fluid flow rates in different parts of the chip. A team of engineers and chemists from UC Santa Barbara, the University of Virginia, and the University of Southampton has devised a method to address this problem. In the new method, a single variable-frequency pressure source communicates with the microfluidic chip via tubes connected to deformable films (“capacitors”) on the chip. The length of each tube is chosen such that the tubes will have well-separated resonance frequencies. Then, the frequency of the actuator is tuned to drive fluid flow in the desired channel only.

As demonstrated in their recent paper, the authors produced three separate devices with clearly differentiated excitation frequencies (see figure below). In addition, they demonstrated a single device with two separate flow channels that could be switched between by modulation of the driving frequency.

Fluid flow in the chip (left, from Figure 1E) is controlled by a periodic pressure source connected to a deformable film by a tube. By using tubes of different lengths, one can selectively drive fluid flow in a channel by tuning the pressure source to that channel’s resonant frequency (right, from Figure 2A).

The authors state that by utilizing a large range of excitation frequencies it should be possible to independently control up to 10 flow channels on a single chip using their technique. They also project that it should be possible to control multiple channels simultaneously by employing an excitation signal incorporating multiple frequencies. Thus, this new flow control technique has the potential to be an elegant and low-cost solution for many types of diagnostic applications.

Read this article in Lab on a Chip today:

Flow switching in microfluidic networks using passive features and frequency tuning
Rachel R. Collino, Neil Reilly-Shapiro, Bryant Foresman, Kerui Xu, Marcel Utz, James P. Landers, and Matthew R. Begley
DOI: 10.1039/c3lc50481f

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