Marloes Groot: ‘Deeper, faster imaging, that’s our goal’
'It would be great to have more techniques enabling us to look directly into the patient’s head.’ Professor Marloes Groot is a physicist working at the Laser Centrum Vrije Universiteit. As (co)leader of the program Photonics and Life Cell Imaging, she is responsible for new imaging techniques.
She explains her group has the technology to create images of objects measuring between 50 nanometres and 50 micrometers. Single cells can be made visible within this range.
Groot’s group faces some challenges in achieving this goal. Groot: ‘To keep the tissue as intact as possible, we eventually want to eliminate using external dyes, like Green Fluorescent Protein. Also, we need techniques with good penetration. We use clever laser pulses that directly detect the intrinsic properties of the tissue.’
Groot’s lab houses a range of different imaging techniques. Very important is non-linear microscopy. Instead of using one photon to excite a particle, this technique uses two, both with a lower energy. ‘Because two photons are required for excitation, we can very precisely control at what depth we like to image. Another advantage is that because of the longer wavelength of the separate photons, they scatter less and can penetrate deeper into tissue.’
Many techniques, Groot says, cannot be used when studying live humans, which is the ultimate goal for many neurologists. Optical coherence tomography however, or OCT, does enable doctors to take a closer look at patients’ tissues. It is an interferometric technique generating extremely high-quality images, using two laser beams, one of which enters the tissue. From the interference between the control beam and the penetrating beam, computers compose three-dimensional images. A similar technique renders two-dimensional images, which can be made of tissue layers deep within the tissue.
In Groot’s own research, she mainly uses ultra-fast spectroscopy to study proteins and enzymes. She enthusiastically points at a recent Nature publication pinned to the wall. ‘We studied how the double bond between two carbon molecules in the POR-protein is reduced to a single bond. And how the enzyme is switched from an inactive into an active state. This reaction is light-activated, so we were able to induce it ourselves using a first laser pulse. With a second pulse, we made an image of what was happening. It appeared that the reduction takes place in two separate steps. All this happens in picoseconds.’
Helping out colleagues
Groot works at the Laser Centrum Vrije Universiteit, which houses an even bigger range of imaging devices. To name a few: röntgen microscopy, coherent anti-strokes raman (CARS) microscopy and single-molecule fluorescence microscopy. These techniques are not a part of the Neuroscience Campus, but they are open to outside users via an access program and, Groot says, her group does its best to help out where possible with specific imaging issues colleagues might have.
She’s enthusiastic about the cooperation already ongoing within the Neuroscience Campus. ‘It’s unique that we, the physicists, are located so closely to the neurologists. The subjects we study under our microscopes are right next door. We even opened a lab in the B corridor, amidst the mice-researchers.’ Also, Groot has high hopes new collaborations will bring endoscopic applications one step closer to the Campus. ‘In the lab, we have everything functioning. But most experiments are still performed on slices of brains of mice that can be placed under the microscope. It would be great to have more techniques enabling us to study patients directly.’
