Up to five times stronger optical effect - luminescence of carbon nanotubes - has been achieved by the team led by Dr. Dawid Janas from the Silesian University of Technology. The achievement was described in the journal Chemical Communications.

“Just like with the asymmetrical Mona Lisa's smile, which intrigues and remains unexplained since the 16th century, we show that perfect symmetry in the world of nanomaterials is not necessarily desirable. Research results show that a minor chemical modification can significantly improve the optical properties of such materials,” Janas says.

Scientists have developed a precise way of introducing such 'disorder' into carbon nanotubes. When they modified every five hundredth carbon atom, the nanotubes began to glow much more strongly. Thus modified, they can detect disease markers with a higher sensitivity, because when the nanotubes glow more strongly, the light signal can be detected even by simple sensors in medical devices.

Earlier, the scientist developed a method of separating carbon dust into individual nanotubes and selecting them, e.g. by colours. Dr. Janas explained the details of this technology in an interview entitled 'Cinderella 2.0 picks out nanotubes from black dust'.

'SALTED' NANOTUBES GLOW MORE STRONGLY

Along with the possibility of dividing the black powder, which are carbon nanotubes bought by laboratories, into individual ingredients, scientists started dreaming about the possibilities of using precisely separated, colourful nanomaterials, also in medicine.

“Colourful nanotubes, contrary to the intuition associated with carbon, can actually be grouped by colours. The mixture we use for research contains 20-30 types of nanotubes. Individual ingredients have very intense colours, covering the entire visible spectrum. You could with paint images such colours, although this would not be the cheapest dye,” jokes Dr. Janas. 

“That is why it makes more sense to use it as a sensor, for example in medical imaging. Glowing nanotubes now detect cancer markers in patients. We will check whether they can help prevent cardiovascular diseases.”

The dreams of researchers around the world ended when it turned out that while nanotubes had a 'nice and colourful' glow, it was nor very bright - the material would not reflect much light. Therefore, a signal that can be obtained in medical imaging is not strong enough. The problem cannot be solved by using more powder, because the concentration of contrast introduced into the human body should be minimal.

Improving the optical properties of nanotubes became the goal of scientists around the world. Polish researchers succeeded. The team from the Silesian University of Technology decided to disrupt the symmetry of only a few carbon atoms in some nanotubes.

“It turned out that if we introduce some functional groups to the surface of a carbon nanotube, then the symmetry of the nanotube is favourably broken. When we damage the surface of some nanotubes in a controlled manner, the optical performance increases significantly. Everything changes,” says Dr. Janas.

To illustrate the surface defects with an everyday life situation, the chemist suggests imagining a large pot of soup, to which you can add a pinch of salt to make it taste better. A similarly minor modification is needed to significantly improve the luminescence of nanotubes - it is enough to attach a functional group to one carbon atom among five hundred unmodified atoms.

The researcher admits that it has been known for a long time that various functional groups could be added on the surface of nanotubes. However, 'the devil is in the details'. Until now, scientists did not know how to do it without spoiling the properties of the nanomaterial. Polish researchers have shown that by using special compounds - azides (N-N-N), you can not only preserve the colourful glow, but strongly improve.

SIMILAR TO NOBEL PRIZE-WINNING METHOD

Just like the tactics of 'click chemistry’ which was recently awarded the Nobel Prize, the method of 'brightening' nanotubes is also based on azides and uses cycloaddition. The method of attaching functional groups to the surface of carbon nanotubes is a cycloaddition of nitrenes (generated from azides) to alkenes (the surface of a carbon nanotube is only double bonds).

According to Dr. Janas, the reaction meets a number of criteria of 'click' philosophy. Firstly, it runs in a mild environment, and the process conditions are uncomplicated - Polish researchers used water. Secondly, it favours obtaining one type of product that can be purified in a simple manner - the Polish method generates only one type of modification. Thirdly, it has high efficiency; when one unit connects to another, only nitrogen is released.

“What's more, the obtained product is also cyclical,” says Dr. Janas. “This is the core of our discovery - we attach functional groups to the surface of a carbon nanotube with the formation of a ring containing nitrogen, thanks to which carbon atoms retain their sp2 character. This is well illustrated by the diagram below, which is in the publication.”

Diagram comparing the Polish approach (top) to the previous technology, which does not lead to obtaining a cyclical product (bottom).

In the paper published in Chemistry Communications, the scientists have shown that, using azide derivatives, you can easily attach this functional group to the surface of a carbon nanotube to increase its optical properties four or five times. According to the project leader, the team's achievement is a development of the classic 'click chemistry', with nanomaterials being modified instead of chemicals.

PLANS: POLISH-AMERICAN CLINICAL TRIALS

The method will be tested in the United States by a research group from a hospital in New York (where Dr. Janas was a Fulbright Scholar). Polish and American scientists will focus on the study of cardiovascular diseases.

“Before such diseases develop, patients much earlier have problems with fat management in the body. If we deliver carbon nanotubes to the cells, they will go to the appropriate areas of the cell and image the functioning of the parts that interest doctors,” says Dr. Janas.

Scientists are planning tests on cells and animals, and in the future - also with patients. The proposed methods of preventing circulatory system diseases are based on the experiences of American clinicians from tumour imaging. They have shown that an implant containing carbon nanotubes makes it possible to detect cancer markers in the patient's bloodstream, and at the same time prevents the nanotubes from entering the body. In people after cancer, this method allows to monitor on a regular basis whether there has been a relapse.

Perhaps in the future, implantable sensors will warn the doctor and patient very early that fat cells accumulate in the veins and arteries. Thanks to this, it will be possible to implement effective treatment and prevent heart attacks, strokes and coronary artery disease.

Scientists from the Silesian University of Technology conduct research as part of Dr. Janas' National Science Centre project entitled 'ENIGMA: dEciphering Nanochemistry by usInG cheMical modification of cArbon nanotubes for modern medicine'. The research described in Chemical Communications was carried out in collaboration withy researchers from Kyushu University in Japan.

PAP - Science in Poland, Karolina Duszczyk

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