Vienna University of Technology,
Vienna, Austria
www.tuwien.ac.at/en

D r. Saideh Saghafi at the Institute for Solid State Electronics at the Vienna University of Technology has developed the laser technology and the optics for an ultramicroscope that can reveal the tiniest details of biological tissues in three dimensions. It uses laser beams to see inside flies, mice, or medical tissue samples. Using various “optical tricks,” she has turned a laser beam into an extremely thin two-dimensional laser surface, which can shine through samples layer by layer.

Fig. 1 – Microscopy of the head of a fruit fly.

The beam, used in Saghafi’s technique, provides 3D non-destructive sectioning and imaging of a large samples such as tumors, an entire mouse brain, as well as small samples of neurons and spines with micrometer resolution. Figure 1 shows microscopy of a fruit fly’s head, while Figure 2 presents a 3D image of the inside of a fly’s head.

Biological tissue tends to be opaque, with light scattered at the interfaces between different materials. In order to view the internal structure of biological tissue, it must first be made transparent to laser beams. First, the sample is treated so that any water it contains is replaced with a fluid having different optical properties. This enables laser beams to penetrate deeply into the sample, said Saghafi.

Ultra-thin light surfaces

Saghafi used a series of tricks, she explained, to convert a conventional round laser beam into an elliptical beam, which is transformed in turn into a thin layer of light. “The surface of the laser light, which we generate with our lenses, is only around 1.5 micrometers thick. Stimulated by the laser light, an extremely thin layer of the sample begins to fluoresce—and this light can be picked up with a camera,” she said. The basic idea behind ultramicroscopy has been applied at the Vienna University of Technology for some years now, but her thin laser layers have improved the microscopic precision decisively.

Laser light is shone through the sample layer by layer, with an image taken every time. She then used these to construct a complete 3D model of the sample on the computer. Detailed images of tiny fruit files and the complex network of neurons in the brains of mice emerged. “If we didn’t shine the laser surface through the sample, it would be a case of having to cut the sample into thin layers and then put these under a microscope one at a time. Of course, this approach could never match the accuracy we achieve with our ultramicroscope,” explained Saghafi.

Fig. 2 – 3D image of the inside of the fly’s head.

Together with her colleagues, she has created detailed images with previously unmatched quality, which will provide important information for medical research. The novel ultramicroscope is also ideal to investigate and create 3D representations of human tumors from a pathology perspective.

Ultramicroscopy is becoming an increasingly common technique in neuroscience research with high potential in medical diagnostics for cancer and neurological disease detection. The image quality in ultramicroscopy depends on the shape and quality of the light sheet and the innovative method that she created allows a significant improvement in the optical characteristics of the light sheet, including the length and diameter of the line of focus and spatial intensity distribution along the light sheet.

For creating an efficient light sheet microscopy/ultramicroscopy using an innovative beam shaping method of turning a Gaussian beam into an elliptical beam with flattened Gaussian intensity distribution, Saghafi received a Third Place Edmund Optics Grant for Higher Education Optics Programs, Europe. To view a video of the technology, visit www.techbriefs.com/tv/ultramicroscope