Nanophotonics changes protein colours

Scientists of the University of Twente and the AMOLF Institute succeeded in changing the colour of light that is emitted by fluorescent protein molecules, without modifying the molecular structure. By placing the proteins in a photonic crystal, the colour of the light alters. This results in a powerful new tool for investigating the influence of light on biological systems. The coloured proteins are on the cover of April’s Small magazine.

Protein molecules emitting visible light, so called fluorescent proteins, are crucial in scientific research on processes within a living cell. Tuning the colour of light can, up to now, only be done by altering the molecular structure. By using a so-called photonic crystal, the UT scientists have found an attractive alternative. These are highly ordered air spheres with dimensions within the range of the wavelength of light. Because of this ordering, strong interference effects will show: this causes a ‘forbidden range’ of wavelengths, of which no light transmission will be possible inside the crystal. Any light source placed within the crystal will have to transmit its light in another colour or direction.

For the first time, a natural lightsource like a protein is now placed in a crystal. The structure of the crystal has systematically been varied to observe colour changes. Around the ‘forbidden zone’ or stop band, some colours will be enhanced and others suppressed. Thus, using photonic crystals, a whole new range of possibilities opens up for studying biological process, within a new discipline called biophotonic engineering.

The upper two pictures show which colours are reflected by the two crystals: inside the crystals there’s no propagation of light of these specific colours. The second row of pictures show the yellow-orange emission of the protein, shifting towards red and bright green. The spectra show the stop bands as a yellow zone. The ‘up’ arrow shows the amplification of light in the specified wavelength area.

The research has been done within the groups Biophysical Engineering of Prof. Vinod Subramaniam and Complex Photonic Systems of Prof. Willem Vos, both of them part of the MESA+ Institute for Nanotechnology of the University of Twente. This was a joint project with the Institute for Atomic and Molecular Physics (AMOLF) in Amsterdam.

SOURCE : University of Twente