The Nobel Prize in Chemistry

“for discoveries that have enabled optical microscopy to become nanoscopy”

The interplay of fluorescent molecules and smart technology has meant that these researchers have made it possible, with the help of optical microscopy, to study living matter and cells using a high resolution that in the past had only been possible using electron microscopy.
At the time that optical microscopy was developed, it gave humanity the opportunity for the first time to gain an insight into the building blocks that make up our world but are too small for us to see with the naked eye. However, it was soon realised that there was a clear limit to the detecting of small details. In 1873, Ernst Abbe formulated an equation that set this limit. It related resolution to the wavelength of the light used. When visible light is used, the smallest details detectable are 0.2 micrometres apart. For over 120 years, this equation has been regarded as a truth set in stone, but this year’s Nobel Prize winner in Chemistry has succeeded in breaking this law with the aid of fluorescent molecules and smart technology.

: The object to the right of the line of dashes is too small to detect using conventional microscopy.

: The object to the right of the line of dashes is too small to detect using conventional microscopy.

 

THIS YEAR’S NOBEL PRIZE IN Chemistry has been awarded to Eric Betzig, Stefan Hell and William Moerner for their work in circumventing this optical limit. There are two principles developed in parallel that have earned the award.
Stefan Hell is being awarded for the discovery of the principle of STED (stimulated emission depletion). Hell presented STED for the first time in the year 2000. The technology is based on so-called laser scanning fluorescence microscopy whereby a laser beam is used in a microscope to scan the sample that will gradually build up an image. The STED process also involves exciting fluorophores in the sample by scanning them with a laser beam, while a second ring-shaped laser beam is used to stimulate the emission of – that is to say, to extinguish – much of the fluorescence apart from an extremely small area. The extinguished fluorophores do not serve to create the image; only the light from the defined area is registered. Changing the intensity of the ring-shaped laser can control the size of the defined area, thus producing nano-sized resolution. Scanning the sample means that the image is built up nanometre by nanometre. In this way, an image with higher resolution than that foreseen by Abbe can be constructed.

The principle of STED, based on laser scanning microscopy and the principle of extinction by way of stimulated emission.

The principle of STED, based on laser scanning microscopy and the principle of extinction by way of stimulated emission.

THE OTHER principle of nanoscopy is based on the possibility of detecting individual fluorophores. The foundations for this were laid by William Moerner in 1989, when he was the first researcher in the world to demonstrate light absorption from individual molecules. Moerner’s continued research also showed that fluorescence from a variant of fluorescent protein known as GFP (green fluorescent protein) can be switched on and off.

Inspired by Moerner’s research, Eric Betzig developed a technology known as PALM (photoactivated localisation microscopy). PALM is based on so-called photoactivated localisation miscroscopy. By allowing only a few interspersed fluorescent molecules to be activated by a light pulse, these can be registered one by one. However, instead of imaging the fluorescence, the positions of the fluorophores can be determined with a high degree of accuracy. Repeating this process a number of times and lighting up different molecules by building up the image layer upon layer can produce a combined high-resolution image. PALM was demonstrated by Betzig for the first time in 2006.

The principle of PALM, whereby the localisation of individual fluorophores is registered on a one by one basis.

The principle of PALM, whereby the localisation of individual fluorophores is registered on a one by one basis.

ALTHOUGH the breakthroughs in this field are relatively new, a number of variants and similar technologies have already been developed. The three Prize winners are also still active as researchers. Hell, for his part, has applied STED in the study of living nerve cells so as to understand better the synapses of the brain. Moerner has studied the proteins involved in Huntington’s Disease, while Betzig has examined the way cells divide themselves in the embryo, to give just a few examples.

FURTHER RESEARCH AT THE UNIVERSITY of Gothenburg is being done on both the development of similar laser scanning techniques and the methods of applying nanoscopy. The Biomedical Photonics Group is developing further laser scanning microscopy based on multiphoton excitation in order to be able to study biological tissue in a non-invasive way. The focus here is not on achieving higher resolution but rather to be able to produce more in-depth imaging of living systems so as to monitor processes and the effects of medicines on tissue. Research has, for example, great significance in the ongoing activities at the centre of skin research (SkinResQU), where we are trying to understand the molecular processes involved in skin cancer, allergies and medication administration that affect the skin. The Sahlgrenska Academy has made available a “nanoscope” based on PALM that has recently been installed as part of a public infrastructure facility called “the Centre for Cellular Imaging”. As a result, this is the place where nanoscopy is being applied in several research projects that are primarily in the field of medicine, but the facility is open to all.

2-2014-nobelpriskemi-marica-johan

Johan Borglin, Phd.Student
Biomedical Photonics
, Department of Chemistry and Molecular Biology, University of Gothenburg

Marica Ericson, Associate professor
Biomedical Photonics, Department of Chemistry and Molecular Biology, University of Gothenburg

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