A5: Bio-Photonics

Bio-photonics addresses the interaction of light and animate matter, with emphasis on the nanometer scale. This comprises two equally important but distinct aspects: (i) Using light to manipulate objects on the surface of or in cells in a desired and well-controlled fashion, and (ii)using light as a local probe to observe biological processes or biomolecule interactions. Research on bio-photonics at the CFN comprises work on (i) next-generation optical tweezers and (ii) optical biosensors.

Since their invention in 1986 by A. Ashkin [1], optical tweezers have become valuable tools for research in the biological and physical sciences. Using a focused beam of light to trap and move matter, optical tweezers offer convenient, non-invasive access to processes at the mesoscopic scale [2]. Existing optical tweezers, however, have two major limitations: Firstly, the minimal size of trapped particles is limited and secondly, only small numbers of particles can be handled by one tweezer. It is our aim to develop next-generation optical tweezers that can be reliably used in biomedical applications.

A second limitation of recent optical tweezers is the limited size of particles that can be trapped in the light focus usually produced by a microscope lens. The size of the focus is limited by the numerical aperture of the lens and, more fundamentally, by the wavelength of light. As a consequence particles with diameters below a certain value (typically some tens of nanometers) can not be handled.

Biosensors are capable of recognizing and capturing a specific target molecule. In optical sensors, light is used to measure changes at the surface caused by the binding of the target molecule quantitatively and, ideally, in real time. If the target molecule is pre-labeled with fluorophores, binding can be detected with high sensitivity using established fluorescence techniques. In integrated optical sensors and lab-on-the-chip applications optical technologies will enable a massive parallelization and miniaturization [3].