Optical tweezing creates 3-D structures

Scientists have created three- dimensional structures of particles using laser technology, which could help develop greater understanding of the study of extended crystalline structures and potentially impact on biological issues such as tissue growth.

These latest advancements in optical tweezing techniques developed by physicists at the University of St Andrews have been unveiled in tomorrow’s (Friday 10th May, 2002) issue of the international journal ‘Science’.

In their paper, ‘Creation and manipulation of three-dimensional optically trapped structures’, Dr Kishan Dholakia, and his colleagues Dr Michael MacDonald, Dr Jochen Arlt, Professor Wilson Sibbett, Lynn Paterson and Karen Volke-Sepulveda, describe how they have created 3D arrays, or groups, of particles using laser light to hold them together with the ‘optical tweezers’ technique.

It is the first time that true three-dimensional particle structures have been created and manipulated using laser light in this way, and the development could mean advances in the understanding of a broad range of issues in physics, biology and chemistry.

“Ultimately we are aiming for a method which will allow us to create extended 3D arrays of particles in a pre-determined order which could allow us to look at defects in crystal structures. We are trying to understand fundamental physics as well as bio- problems such as tissue growth and organisation,” said Dr Dholakia.

The findings are the latest in ongoing advancements in optical tweezer technology, a technique pioneered in the 1970s in which particles are trapped in a tightly focused laser beam and can be moved from one spot to another. Miniscule objects such as a glass particle can bend – or refract – the light, which can then act like a lens. This causes forces to be exerted on the object as the light passing through it changes direction. This leads to the particle being attracted, or sucked into, the brightest region of the beam and staying there. It does this without any damage to the particle. Several applications for optical tweezer techniques exist in biology including the stretching out and studying of DNA.

A year ago the St Andrews Group found a way to make miniscule objects, from glass beads to hamster chromosomes, ‘spin’ using optical tweezer techniques, giving an unprecedented amount of control over the position and orientation of such objects.

It was during this research and creation of 2-D structures using laser light, that they realised that they could create an extended three-dimensional structure by using multiple tweezers (multiple laser beams) in special patterns of light.

“The major motivation for this research is the worldwide demand from scientists who are interested in creating 2D and 3D structures to order, so that they can observe the way other particles collect or aggregate around this central structure,” said Dr Dholakia.

“The dynamics of how these complex systems behave and how the particles within them might organise themselves under a variety of conditions is the subject of intense worldwide investigation, and of central importance in industry and basic science. Our cubic structures could allow real 3D investigations of these effects. Using such a system one creates a kind of template which can be used to observe the way particles organise themselves.

“Importantly, studying ordered arrays has not only excellent uses for biology and chemistry but the ordering and behaviour of these systems allows scientists insights even into areas such as superconductivity, photonic bandgap materials and electron or atom transport,” he continued.

“In terms of nanotechnology our work enhances the ‘optical toolkit’ and use for lab-on-a-chip systems, as we can create and assemble three dimensional structures at the microscopic level using our methods. To date very limited work has been done in 3-D and most work is currently done at the two-dimensional level. We can make three dimensional cubic like structures. This ability is ideally suited to bioengineering as optical tweezers are very good at grabbing biological material, such as cells and chromosomes,” he said.

Dr Dholakia is head of the Optical Trapping Group at the University of St Andrew’s School of Physics and Astronomy. The group’s work is funded by the EPSRC (Engineering and Physical Sciences Research Council), The Medical Research Council UK, The Royal Society London and CONACYT in Mexico.

ENDS

NOTE TO EDITORS:

DR DHOLAKIA IS AVAILABLE FOR INTERVIEW ON 01334 463184 / 463165.

THE EMBARGOED SCIENCE PAPER IS AVAILABLE BY EMAILING [email protected]

NOTE TO PICTURE EDITORS:

PICTURE CAPTION:

“Left – Representation of the 3-D array of particles ‘trapped’ by laser light. Right – The top row shows the cubic structure rotating under laser light. The bottom row shows the collapse of the structure when the laser is switched off.¿

EMAILABLE IMAGES OF THE 3-D STRUCTURES ARE AVAILABLE FROM GAYLE COOK – CONTACT DETAILS BELOW.

Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050103, or email [email protected] Ref: Kishan Science pr 090502 View the latest University news at http://www.st- andrews.ac.uk/extrel/press.htm