Optical trapping and tweezing

When light-absorbing particles encounter strong EM field gradients they have a tendency to gravitate to the most intense region; when the EM field is a laser beam, the laser beam acts as an “optical trap”, and can be used to manipulate the particle by controlling its motion, through so-called ’optical tweezing’. The emerging field of optical tweezing and trapping has found many applications, most notably in biosciences for optical tweezing, trapping and micro-manipulation of biological samples for particle sorting, cooling, trapping and rotation, to name but a few. The wide dynamic range in trapping sizes allows for a plethora of biological objects to be manipulated, ranging from single live cells to individual molecules, such as nucleic acids and proteins.

Single molecules can be manipulated with nanometre precision through this technique and used as a force transducer to apply or measure forces in the pico-Newton range, with special resolution in nanometres and temporal resolution of milliseconds. Thus the technique allows one to investigate interactions between individual molecules, something that was not previously possible.

Our work focuses on the experimental development of optical tweezing systems for the three-dimensional trapping and manipulation of particles using novel laser beam shapes, including non-diffracting, vortex and flat-top beams. By integrating a spatial light modulator with the trap, we are able to create complex traps through the design of suitable digital holograms.

The relevance of the work is in applying the optical tweezer to trap and manipulate micron and sub-micron biological structures, as well as for the measurement and control of flow in micro-fluidic systems.

Other projects: