Jackie Cockrill, Publishing Assistant

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Freezing the action in living things

10 Nov 2010

A fast, high-resolution infrared imaging technique that can ‘freeze’ living specimens has been designed by UK scientists and tested on human ovarian cancer cells. The technique could lead to a better understanding of how cancer drugs work.

Infrared spectroscopy of cell images can be used in a number of fields including forensic science and cancer research. However, taking pictures of samples can take up to 12 hours. Chris Phillips and his team at Imperial College London have developed a technique to produce 2D images that takes a fraction of a second. By combining a purpose-built pulsed IR laser source with a charge-coupled device camera, rather like a digital camera, they were able to generate pictures 1011 times faster than current IR spectroscopic imaging methods. The IR source generates very short pulses (~100 psec) that keep the illumination levels below cell phototoxicity limits and allow moving specimens to be frozen in a way that mimics conventional flash photography.

Previous attempts to image cells in this way have required long illumination times, which causes the cells to move away from the light source or can kill them. ‘Because you can do it so quickly, you can freeze the action in living things, and because you have so much more light signal, you can get right inside the cells to take chemical maps,’ says Phillips.

The sharpest focus cell images are visually selected for the cell-level spectroscopy analysis

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Link to journal article
Ultrafast infrared chemical imaging of live cells
Hemmel Amrania, Andrew P. McCrow, Mary R. Matthews, Sergei G. Kazarian, Marina K. Kuimova and Chris C. Phillips
Chem. Sci., 2011, DOI: 10.1039/c0sc00409j

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Rapid cell extraction using droplets

01 Sep 2010

An aqueous two-phase microdroplet system that isolates and extracts cells could aid research into tissue engineering and regenerative medicine, say UK scientists.

Droplet-based microfluidic systems, using a fluorescence-based detection method have been used to locate, identify and discriminate cells within a specific droplets and more recently two-phase systems have been investigated for their ability to separate different biological materials. Target cells distribute between phases by their own thermal motion to reach equilibrium but so far this has proved a slow process.

Now, Andrew deMello and his team at Imperial College London have devised a novel method to separate cells using microfluidic droplets. The process could enable high throughput cell separation which would be ideal for clinical applications such as cell therapy and regeneration.

A PEG microdroplet completely encases the DEX droplet

In deMello’s device, human T lymphoma cells enter the microdroplet system within a dextran solution. At a T-junction in the device, the dextran meets a polyethylene glycol (Peg) inlet where a droplet of Peg completely encapsulates a dextran droplet. These droplets then follow a winding channel in the device that causes both phases to mix – forming an emulsion and allowing the cells to experience the environment of both phases. When the two phases separate back into a double droplet, the cells remain in the outer Peg phase.

Binding the cells with an antibody-N-isopropylacrylamide (Ab-NIPAM) is crucial to the separations explains deMello as this makes them favour the Peg phase. Without the Ab-NIPAM, 98 per cent of the cells remain located within the dextran. But once bound this reverses to 93 per cent moving to the outer Peg droplet.

Shashi Murthy, an expert in microfluidic devices design at Northeastern University in Boston, comments that conventional approaches ‘are quite effective, but there’s a lot of interest in trying to make them more simple and as microfluidic systems are being proposed as disposable and cheap alternatives to more expensive instrumentation, this is of significant interest.’

The team believe that the technique will be able to separate heterogeneous cell populations in a high-throughput manner. Also, the use of Ab-NIPAM conjugates can be applied to a wide range of other cell systems simply by changing the antibody.

Rapid cell extraction in aqueous two-phase microdroplet systems
Kalpana Vijayakumar, Shelly Gulati, Andrew J. deMello and Joshua B. Edel, Chem. Sci., 2010
DOI: 10.1039/c0sc00229a

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