Scientists have known for centuries that light photons could “push’ objects via its scattering force. In 1691, Johannes Kepler discovered that photons within a beam of light could force microscopic particles to travel along with light beam, noting that a comet’s tail always faces towards the sun.
In 2011 researchers from China and Hong Kong took Kepler’s discovery much further, theorizing that light beams could actually draw objects towards the light. NASA also conducted a study to see how light could be used to help manipulate samples in space.
The St. Andrews and ISI research team, which was led by Dr Tomas Cizmar, Research Fellow in the School of Medicine at the University of St Andrews, and assistants Dr Oto Brzobohaty and Professor Pavel Zemanek from ISI, have developed a technique that allows them to use “negative” force on microscopic particles.
According to a press release issued by the University of St. Andrews, this is the first time the concept of “pulling” particles through the use of negative force has been realized. Although the beam may be minuscule compared to the one used aboard the USS Enterprise, the goal of the research was to create a light beam which was capable of targeting single cells in the human body, moving the cell to a particular location. They hope the discovery can be applied in a variety of ways in bio-medical photonics.
The beam’s negative force acts on very specific properties of an object, such as the size of the object and what particles make up the object. Cizmar said the team was particularly interested in testing to see if the beam could separate white blood cells. He went on to tell Science Recorder:
“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.”
The size of the objects which can be transferred is limited due to the amount of energy required to move larger objects. The more energy used, the more heat is created. Cizmar told Space Travel:
“The problem is that this is based on the transfer of momentum between photons and the object, and unavoidably there is also a transfer of energy. If you imagine you would like to attract a football, the amount of energy it would transfer would be huge and it would immediately burn up the football.”
A Phys.org report states that the team also discovered that in certain conditions, the objects held by the “tractor” beam would re-arranged themselves into a structure that made the beam even stronger. Cizmar said:
“Because of the similarities between optical and acoustic particle manipulation we anticipate that this concept will provide inspiration for exciting future studies in areas outside the field of photonics.”