Stelzer Group

Previous and current research

Modern biophotonics provides many technologies that operate in a nanodomain. The precision of optical tweezers is less than a single nm, the resolution of optical microscopes is in the range of 100 nm, laser-based nanoscalpels generate incisions 300 nm wide and cause severing that is barely 700 nm deep. Extremely efficient light microscopes require nanoWatts of power to induce fluorescence emission.

Although many modern technologies could operate in 3D, they are still mainly applied in a cellular context that is defined by hard and flat surfaces. On the other hand, it is well known that relevant physiological information requires the geometry, the mechanical properties, the media flux and the biochemistry of a cell’s context found in living tissues. A physiological context excludes single cells on cover slips. It is found in more complex 3D cell structures.

However, the observation and the optical manipulation of thick and optically dense biological specimens suffer from two severe problems. 1) The specimens tend to scatter and absorb light, so the delivery of the probing light and the collection of the signal light both become inefficient. 2)Many biochemical compounds (most of themnon-fluorescent) absorb light, suffer degradation of some sort and induce malfunction or even death.

The group applies and develops technologies for the observation of large and complex 3D biological specimens as a function of time. The technology of choice is the light sheet-based fluorescence microscopy (LSFM), which illuminates a specimen from the side and observes it at an angle of 90°. The focal volumes of the detection system and of the light sheet overlap. True optical sectioning and dramatically reduced photo damage outside the common focal plane are intrinsic properties. EMBL’s implementations of LSFM are the single plane illumination microscope (SPIM) and its more refined version (DSLM). LSFM take advantage of modern camera technology and are combinable with essentially every contrast and specimen manipulation tool found in modern light microscopes.

Future projects and goals

The optical path in LSFM is designed to allow high flexibility and modularity. We successfully integrated our nano-scalpel and devised a toolbox of photonic nano-tools. We plan to integrate them into our light sheet-based fluorescence microscopes and apply them to complex biological objects.

We developed a technological basis that integrates LSFM with perfusion cell culturing units. Time-lapse imaging of cell cultures for several days under controlled temperature conditions provides model systems for studying organ morphogenesis. We will investigate the influence of localised mechanical forces on cell function by inducing perturbations in cellular systems. Typical relaxation experiments include cutting actin fibres and microtubules, optical ablation of cells contacts, manipulation of sub-micrometre particles and the stimulation of selected compartments with optically trapped probes.

Amongst the biological specimens we currently use and intend to use in the future are Drosophila, zebra fish and amphioxus. A major effort is placed on the investigation of multi-cell structures such as spheroids and cysts. The group integrates the efforts of engineers as well as biologists, physicists and mathematicians.