Modern biotechnologies increasingly require devices capable of moving around single biomolecules, cells and other micro-objects. The first appliance of the kind, laser optical forceps, was developed by the group led by Arthur Ashkin, an American physicist, back in 1986; more new technical solutions emerge each year. A research group based at Saratov State Technical University, and Tantal, JSC, suggested and developed a micromanipulator that can handle and move up to seven microparticles simultaneously.
It is possible to say that the way to the optical forceps — or, using a more correct term, a laser micromanipulator — was cleared by Petr Lebedev, a distinguished Russian physicist, back in 1910, during his experiments to discover the light wave pressure. The force of this pressure draws in polarised dielectric microparticles to the focused laser emission area. Thus, it allows to move them following the light focus.
In this kind of scheme, it is necessary to ensure extremely accurate matching of focus and micro-object to allow initial particle capture. Therefore, axicons — optical elements that focus laser emission in a straight line segment several millimetres long instead of a point — are used in the manipulator design to facilitate capture.
Axicons can be made of zonal or holographic plates, regular structures that form periodic optical pictures in the space. And most recently, in 2008, Germany-based HoloEye launched batch production of phase modulators — axicons based on an LCD matrix. It is now possible to change spatial pictures of emission dynamically which allows to create sophisticated microstructures.
The research group led by Vil Baiburin developed its optical forceps design based on the German phase modulator and a powerful infrared laser. The resulting system is able to capture and move from five to seven micro-objects simultaneously. That is what constitutes its main advantage as industry manipulators used abroad work with each particle separately. This device will be of a broad use in biophysics in order to study cells. The LCD matrix allows independent control of the object locations without any mechanical interference, as well as building complicated microstructures.
Source of information:
V. B. Baiburin, Yu. P. Volkov, S. D. Spitsin, A. V. Lyashenko: “The Holographic Laser Micromanipulator.” The Heteromagnetic Microelectronics,” issue #2, 2011.