Freezing the action in living things

10 November 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

The team took a series of single shot images of live human ovarian cancer cells, at a wavelength which gave a clear contrast between the nucleus and the cytoplasm of individual cells undergoing multiplication.

Neil Hunt, an expert in IR spectroscopy at the University of Strathclyde, Glasgow, UK, says: 'this seems to be very interesting in that it's using ultrafast laser technology to produce microscopy images, which gives the advantage of much improved sensitivity in relation to methods that have been previously used for infrared microscopy.'

Phillips says that there are two areas for possible applications. The first is collaborating with oncologists to track the internal chemistry of cells and the population of cells being dosed with cancer drugs to aid the understanding of how the drugs work. The second is to take a slice of tissue, normally used for a biopsy, and image it with their camera - allowing measurement of chemicals in the cells, which will ultimately distinguish between cancerous and healthy tissue. 'I think that's where it might make its biggest and earliest impact,' says Phillips.

Anna Watson


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