Scallop eyes as inspiration for new microscope objectives

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The Schmidt objektive produces detailed images of neurons in a mouse brain. Credit: Anna Maria Reuss (USZ) & Fabian Voigt (UZH)

Neuroscientists at the University of Zurich have developed innovative objectives for light microscopy by using mirrors to produce images. Their design finds correspondence in mirror telescopes used in astronomy on the one hand and the eyes of scallops on the other. The new objectives enable high-resolution imaging of tissues and organs in a much wider variety of immersion media than with conventional microscope lenses.

Some species of mussels can see. Scallops, for example, have up to 200 eyes that help them detect predators such as an approaching starfish. However, the eyes of scallops differ significantly from the human eye. While in our eyes the combination of cornea and lens creates an image on the retina, in scallop eyes light is focused by a hemispherical mirror.

Hexbyte Glen Cove Optical imaging with lenses or mirrors

Creating images with mirrors instead of lenses is especially common in astronomical telescopes, in order to capture as much light as possible from planets, stars and galaxies. In the Schmidt telescope developed in the 1930s by Bernhard Schmidt (1879-1935) and still in use in many observatories today, a thin corrective is combined with a large spherical mirror.

Mirror objectives are rarely found, however, in microscopes used to study the biological microcosmos. Most objectives are so compact that they can easily be assembled from lenses. However, to achieve the highest image quality, 10 to 15 lenses made of different types of glass are required, all of which must be precisely polished and accurately aligned with each other. As a result, the cost of microscope objectives for research can be equivalent to that of a medium-sized car, representing a significant portion of the total cost of a microscope.

Hexbyte Glen Cove Compatibility with different immersion media as stumbling block

In addition to their complex design, many commercial objectives have the disadvantage that they are usually designed for one specific immersion medium only, such as air, water or oil. This means that a new objective must be purchased for samples requiring a different immersion medium.

For a long time, this was not a major problem, but in recent years, processes known as clearing techniques that can make transparent have attracted a lot of interest in biology and pathology. For example, instead of laboriously preparing thin tissue slices from a removed mouse brain, clearing techniques can make the whole brain transparent.

In pathology, the hope is that clearing techniques will increase the efficiency of biopsy-specimen examinations, making it possible to diagnose malignant tissue changes such as tumors earlier, for example. Unfortunately, however, most clearing techniques use immersion media that are incompatible with conventional microscope objectives. This means the considerable advantages of clearing techniques for research remain partially untapped.

Hexbyte Glen Cove High-resolution microscopy in large transparent tissue blocks

To circumvent the limitations of conventional microscope objectives, and inspired by the eyes of scallops, which in principle function like small underwater Schmidt telescopes, UZH neuroscientist and amateur astronomer Dr. Fabian Voigt developed an unconventional approach: he realized that it was possible to fill a Schmidt telescope with a liquid immersion medium and shrink it to the size of a microscope.

The resulting objective is quasi a miniature telescope that has been submerged and still provides a sharp image. “It is possible to design a Schmidt objective in a way that it provides excellent image quality in any homogeneous fluid as well as in air,” says Voigt. This means that a single Schmidt objective is compatible with many different clearing techniques. The reason for this unusual feature is the use of a mirror instead of lenses. A spherical mirror focuses light at the same point whether it is immersed in liquid or is in the air.

Hexbyte Glen Cove Versatile applications also in medical diagnostics

To demonstrate the versatility of this innovative approach, researchers working with Fabian Voigt and UZH professor Fritjof Helmchen used their prototype Schmidt objective to study a variety of samples, including mouse brains, tadpoles and chicken embryos. Together with a team from Maastricht University, they were also able to analyze cleared human brain samples. In addition, the new type of objective is also suitable for measuring neuronal activity in the brains of live young zebrafish larvae.

“In all cases, the image quality was equivalent to or even better than that achievable with conventional objectives—even though the Schmidt objective consists of only two optical elements,” Helmchen explains. Compared to conventional objectives, which have about a dozen more lenses, a Schmidt objective can therefore be manufactured much more cost-effectively.

Future applications could also include the examination of tumor tissues or the detection of neurological diseases. “In this respect, scallops could show us the way to improved medical diagnostics,” says Helmchen.

The study is published in the journal Nature Biotechnology.

More information:
Fabian Voigt, Reflective multi-immersion microscope objectives inspired by the Schmidt telescope, Nature Biotechnology (2023). DOI: 10.1038/s41587-023-01717-8.

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Bees can help prove avocado crops are free of a pathogen that could be a barrier to Australia’s exports

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Honeybee on avocado flower. Credit CSIRO/Dr. John Roberts

Researchers at The University of Queensland and CSIRO, Australia’s national science agency, have shown bees can help prove Australia’s valuable avocado crop is free of a pathogen that could be a barrier to exports. The findings are published in the journal Phytopathology.

Associate Professor Andrew Geering from the Queensland Alliance for Agriculture and Food Innovation (QAAFI) said monitoring for sunblotch is important to protect lucrative overseas markets.

“We’ve had an active control plan for avocado sunblotch since the 1980s because it has the potential to decrease yield of a tree by about 80%,” Dr. Geering said.

“Even though this pathogen has nearly been eradicated, there is a chance there are still pockets of infection around the place, and this is a concern for Australia’s trading partners.

“Because the viroid is seed-transmitted at a very high rate, a child in New Zealand using an infected avocado seed for a school project could introduce sunblotch to their country.”

CSIRO scientist Dr. John Roberts has worked on bee health and biosecurity for more than a decade and developed the concept after detecting many plant viruses alongside bee viruses in pollination hives.

The research team sought a simple way to check for avocado sunblotch in Australian orchards without having to individually test every tree, and found were the answer.

“Avocado trees are 10 meters tall by 5 meters wide and there might be 20,000 in an orchard, and we needed a way to efficiently gather samples,” Dr. Geering said.

Avocado sunblotch in an orchard. Credit QAAFI/Dr. Lara Pretorius

“Bees are brought in to pollinate the trees as a normal farming practice to improve yields.

“They take the pollen back to a central location, their hive, so effectively they’ve done the sampling work for us and all we have to do is test the pollen.

“It’s much better than a team of people climbing up ladders or riding cherry pickers to collect leaves.

“Bees are reliable, free and very thorough in their sampling activity.”

Dr. Geering plans to implement the bee surveillance more broadly.

“Now that we’ve demonstrated the principle, we’d like to roll it out in the largest avocado producing area in Australia, the Atherton Tableland, to demonstrate that it’s free of the pathogen,” he said.

Dr. Roberts said there was great potential for bees to be recruited for surveillance tasks with approximately 530,000 commercially managed hives delivering paid pollination services around Australia for 65% of our horticultural and agricultural crops.

“For avocado sunblotch we can use them for annual monitoring during pollination across wide areas,” Dr. Roberts said.

“This approach can also provide surveillance for multiple pathogens simultaneously of both honeybees and plants, making this a powerful cross-industry biosecurity tool.”

More information:
John M. K. Roberts et al, Surveillance for Avocado Sunblotch Viroid Utilizing the European Honey Bee (Apis mellifera), Phytopathology (2022). DOI: 10.1094/PHYTO-08-22-0295-R

Bees can help prove avocado crops are free of a pathogen that could be a barrier to Australia’s exports (2023, March 30)
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