Turning cells into living lasers

At the Humboldt Centre for Nano- and Biophotonics (HCNB), Malte Gather and his team are researching how light can be specifically controlled and used. Gather came to Cologne for this research in 2019 with a Humboldt Professorship from the University of St Andrews in Scotland. The Alexander von Humboldt Foundation’s programme brings top researchers to Germany who were previously working abroad.

Since then, Malte Gather has been pursuing a whole series of new research approaches that can be applied in almost all areas of life: in smartphone displays, medical instruments or microscopy and sensor technology, the targeted use of light is essential, but far from simple. There are hurdles that have been difficult to overcome so far, making some fields of research sound as if they were actually taken from a film script.

For example, living lasers. Gather is a pioneer in this field. He was one of the first scientists to successfully generate laser radiation in living cells and was even entered in the Guinness Book of World Records in 2013. Since then, Gather and numerous other groups around the world have developed what were initially complicated and impractical living lasers into a useful technology.

The key component lies in microscopically small spheres or discs, so-called microresonators, in which light can be captured and amplified many times over. If these microresonators are embedded in a cell, the cell starts to laser after excitation by an external light pulse. “We turn the cell itself into a light source – and with a precision that surpasses conventional fluorescence methods,” says Gather. The microresonator emits light of a single wavelength, just like a technical laser. The laser emission from living cells is surprisingly stable and accurate.

For example, the team was able to investigate the force dynamics of micrometre-sized protrusions that are involved when cancer cells invade surrounding tissue and whose mechanical forces could not previously be analysed with a microscope. They also used the new method to observe detailed changes in the forces exerted by podocytes, specialized kidney cells, during kidney injury. Gather and his team want to further develop what has so far only worked in the Petri dish into a commercial system that could be used in future, for example for screening active ingredients in drug research.

It takes a village to innovate

For Gather, the Humboldt Centre for Nano- and Biophotonics is characterized by its collegial research culture and the close cooperation between different disciplines. Physics, chemistry and biology all come together there. In this way, the centre has the potential to establish itself as a catalyst for new ideas and as a breeding ground for highly collaborative junior research groups.

Gather was also able to attract some colleagues from his former place of work, the University of St Andrews, to Cologne for the Centre. One researcher who already worked in his team in Scotland is Dr Andreas Mischok. The physicist has dedicated himself to filter and display technology, and his research is set to take the state of the art a decisive step further.

Optical filters and displays, such as mobile phone or television screens, have a fundamental problem: angular instability. When light passes through an optical filter at an angle, the colour or intensity of the transmitted light changes compared to the straight incidence of light. This phenomenon is familiar from laptop screens, which used to display a dark and sometimes colour-inverted image when viewed at an angle. While this problem has largely been resolved in smartphone displays and on computer monitors today, it has come at the expense of the screen’s energy efficiency and colour saturation. While this is merely a nuisance on a mobile phone, it is still a real obstacle for other applications and devices that require extreme precision.