New light shed on drug-delivery techniques

Thursday 27 November 2003

Scientists at the University of St Andrews have developed non- invasive methods of moving and manipulating biological cells using lasers, which could have important implications for future methods of drug-delivery.

In collaboration with colleagues at Illinois Wesleyan University, the new system – based on ‘optical trapping’ methods developed by the physicists have proved almost 100% accurate.

Dr Michael MacDonald and Professor Kishan Dholakia of St Andrews in collaboration with Professor Gabe Spalding of Illinois Wesleyan University used light to sort and separate protein microcapsules, which are used in drug delivery and bio-medicine. The importance if this development is that it is simple, accurate and totally non- invasive.

Dr MacDonald said: “We believe we have only touched the surface with this technology: the method is non- invasive and could have important bio-medical implications and longer term real commercial implications.”

To perform the manipulation, the team developed a new sorting machine, which can separate cells and other objects using light alone. The prototype, described in this week’s edition of Nature, could evolve into an inexpensive component for ‘lab-on-a-chip’ systems for use in physical and biomedical research centres.

The University of St Andrews is a World-leader in the development of optical trapping techniques, and the field has seen amazing advances in recent years. The methods have the potential to assist in the safe and non- destructive delivery of therapeutic molecules into cells, leading to possible new, improved methods for drug delivery. The techniques could have potential benefits for a range of medical applications such as gene therapy, the delivery of anti-cancer agents and the destruction and removal of arterial plaques, one of the causes of heart attacks and strokes.

Professor Dholakia explained: “At the microscopic level forces of light can result in some quite amazing effects including transporting and moving objects. Light spots can grab and hold particles rather like an optical vice or trap. In this particular example we have used light to sort and separate objects according to their size and physical properties.”

The new technology developed could rival FACS – fluorescence- activated cell sorting. FACS is commonly used to separate out biological cells but only works on fluorescent particles. The new system is simple to use, has a sorting efficiency of over 96% and could be useful for a very wide range of matter.

The sorting was done by flowing particles through a three dimensional light lattice or grid created by the interference of many laser beams. As the objects flowed through the grid they had a different likelihood of being held up (grabbed) by the bright spots of the pattern. By careful adjustment of the flow rate and type light pattern, some were held up and others went straight through. The particles that were held up were deflected at angles up to 45 degrees and separated from the original flow.

“The large angle deflection of the fraction we want is key to getting the “sorted” part of the sample you’re interested in out of the main flow as quickly as possible and stopping any jamming occurring,” the team explained.

“Sorting biological objects including cells and chromosomes or taking out a fraction is a key biological requirement. The main technologies that exist are gel electrophoresis, where an applied electric field drives DNA in one direction and the viscous gel drags it in the opposite direction. Optical sorting could build the next generation of this technology that is, for the first time, non-invasive and totally reconfigurable.

“In point of contact healthcare we could envisage a patient giving a small sample, which the system could sort and diagnose what is happening in real time. Optical technology is ideal for this type of work.”

The work was funded by the UK Engineering and Physical Sciences Research Council and performed in the Optical Trapping Group in the School of Physics and Astronomy headed by Professor Dholakia.



Dr Mike MacDonald: email mpm4@st- or Tel 01334 463165; Professor Kishan Dholakia: kd1@st-; Tel: 01334 463184 Professor Gabe Spalding at the University of Illinois Wesleyan University: [email protected] on 001 (309) 556 – 3004


Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050 103, or email [email protected] Ref: New Light Sheds Science pr 271103 View the latest University news at

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