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New ONEM Microscope to combine best of two worlds

Leiden physicists have been awarded 1.5 million euros for developing a hybrid microscope that provided nanometer-resolution. 'The idea is to combine the resolution of electron microscopy with the pros of optical microscopes.'

A new imaging technique is to image individual proteins and other biomolecules at 5-nanometer resolution, which is slightly larger than an individual atom. The technique is called Optical Near Field Electron Microscopy, ONEM in short, by physicists in Leiden, Vienna and Prague, who are going to develop it during the coming years. ONEM should be suitable for imaging other materials such as metals.

This will open up new possibilities for biomolecular and biomedical research, but also for research into batteries, electrolysis or catalysts, says Sense Jan van der Molen, a physics professor at Leiden University. For developing the technology, his research group receives 1.5 million euros from the European FET Fund (Future and Emerging Technologies).

The idea is to combine the nanometer resolution of electron microscopes with the ease and non-destructiveness of optical microscopy. 'The ultimate goal is to film living processes, without causing harm.'

Simulation of a near-field shadow as ONEM would image it

Biological tissue

This is how an ordinary light microscope works: one shines light – electromagnetic waves – on the research subject. The light waves that reflect yield the image.

Visible light waves are easy to use and don't cause harm to biological tissues. However, since the waves are about a micrometre in size, smaller details than this are not resolvable.

Electron microscopes, on the other hand, can provide much higher resolutions. According to quantum mechanics, electrons are waves, too, and their wavelength is much smaller. So electron beams can image objects with much higher resolutions.

One big drawback is that one needs vacuum for electron microscopy, which is a very bad match with the soft, watery environment that proteins function in. Moreover, the electron beam damages the sample very quickly, says Van der Molen, 'soft materials such as proteins are not realistically imagable without damage.'

Reverses television tube

A few years ago, Thomas Juffman, leader of the Vienna group, thought of a way to combine the best of both worlds: the ease and lack of damage of optical microscopy, and the resolution of electron beams.

The trick is to use the photoelectric effect. Light that hits a metal, kicks electrons loose from the metal. This effect, which yielded Albert Einstein his Nobel prize, can turn a layer of metal into a sort of reserved television tube: the impinging light is translated into a pattern of radiated electrons. Using the Low Energy Electron Microscope (LEEM) of Van der Molens group, these electrons can then be imaged.    
But what about the limited resolution of light? 'That concerns the far-field', says Van der Molen, 'while we measure the near-field.' The far-field consists of all electromagnetic variations that propagate like waves, which we know as visible light. But in a closer range, there are also electromagnetic vibrations that extinguish at larger distances. This so-named near-field doesn't suffer from the restricted resolutions, but can only be measured very close to the source. 'This is why you have to image them very close to the sample. The closer, the better the resolution', says Van der Molen.

Spontaneous Combustion

The sample should be very close to a material that radiates electrons easily. Van der Molen: 'for this, you need the most un-noble metals, such as lithium and potassium.' Technically speaking, this is a challenge, since such metals are chemically very unstable. Under air, they ignite spontaneously.

In order to function in the innards of an extremely sensitive microscope, the metal layer will have to be covered, possibly by a thin layer of graphene. How everything is going to function precisely, is the subject of research, which will be undertaken by a PhD student, two postdoctoral fellows and a technician. Funds are also allotted for new hardware.

In the international research project, the Vienna group contributes knowledge about optical microscopy, while Leiden takes care of electron microscopy, partly through part-time professor Ruud Tromp. The Prague group specializes in the proteins to be researched. The German company SPECS is also a participant.

What ONEM can be used for, cannot be predicted exactly, says Van der Molen. 'It's a completely new type of microscope. Once it works properly, it may be useful for a whole range of research, fro biological to chemical and physical research.'

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