A real-life "tractor beam", which uses light to attract objects, has been developed by scientists.

It is hoped it could have medical applications by targeting and attracting individual cells.

The research, published in Nature Photonics and led by the University of St Andrews, is limited to moving microscopic particles.

In science fiction programmes such as Star Trek, tractor beams are used to move much more massive objects.

It is not the first time science has aimed to replicate the feat - albeit at smaller scales.

In 2011, researchers from China and Hong Kong showed how it might be done with laser beams of a specific shape - and the US space agency Nasa has even funded a study to examine how the technique might help with manipulating samples in space.

The new study's lead researcher Dr Tomas Cizmar, research fellow in the School of Medicine at the University of St Andrews, said while the technique is very new, it had huge potential.

He said: "The practical applications could be very great, very exciting. The tractor beam is very selective in the properties of the particles it acts on, so you could pick up specific particles in a mixture."
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It would result in a massive amount of heating... trapping a space ship is out of the question”

Dr Tomas Cizmar University of St Andrews

"Eventually this could be used to separate white blood cells, for example."

Usually when microscopic objects are hit by a beam of light, they are forced along the direction of the beam by the light photons. That radiation force was first identified by the German astronomer Johannes Kepler in 1619 when he observed that tails of comets always point away from the Sun.

Dr Cizmar's team's technique allows for that force to be reversed which he said some people might find counter-intuitive.

"It's surprising," he said. "Only when we looked in detail at the process did we see the reversal. It's quite a narrow field it occurs at."
'Exciting time'

The team at the University of St Andrews worked with colleagues at the Institute of Scientific Instruments (ISI) in the Czech Republic.

Prof Zemanek, from the ISI, said: "The whole team have spent a number of years investigating various configurations of particles delivery by light. I am proud our results were recognised in this very competitive environment and I am looking forward to new experiments and applications. It is a very exciting time."

Practical scientific theories on real-life tractor beams have been developed since 1960, but it is thought this is the first time a beam has been used to draw microscopic objects towards the light source.

Scientists have previously used a technique called an optical vortex to move individual particles using beams of light, but this new approach works in liquids and a vacuum.

The first appearance of a tractor beam in fiction is thought to have been in the American author EE Smith's story The Skylark of Space, which was serialised in 1928. The story contained references to an "attractor beam".

It has been a staple plot device in science fiction television and movies allowing objects like space ships to be trapped in a beam of light, but Dr Cizmar said this particular technique would not eventually lead to that.

He said: "Unfortunately there is a transfer of energy. On a microscopic scale that is OK, but on a macro scale it would cause huge problems.

"It would result in a massive amount of heating of an object, like a space shuttle. So trapping a space ship is out of the question."

Source: http://www.bbc.co.uk/news/uk-scotland-tayside-central-21187598