Flashlights for cancer cells

Scientists have made nanoparticles that can "highlight" a cancerous tumor

MSU Press Service

A group of Russian and French researchers with the participation of scientists from Lomonosov Moscow State University for the first time managed to synthesize nanoparticles from ultrapure silicon with the property of effective photoluminescence, i.e. secondary glow after photoexcitation. These particles are able to freely penetrate into cells, which allows them to be used as luminous markers in the early diagnosis of cancer, as well as in the treatment of this disease. The scientists' article was published in the journal Scientific Reports (Gongalsky et al., Laser-synthesized oxide-passivated bright Si quantum dots for bioimaging).

Research on the search for methods for the synthesis of such nanoparticles is actively conducted in many laboratories around the world, however, according to one of the co–authors of the study, Professor of the Faculty of Physics of Lomonosov Moscow State University Viktor Timoshenko, their quality was unsatisfactory - mainly because they were synthesized by methods of chemical reactions in acid solutions. "The particles were not clean enough," he says, "the remnants of chemical compounds settled on them, which made them toxic. In addition, these nanoparticles had a shape far from spherical, and this did not contribute to the manifestation of photoluminescence. And these two drawbacks severely limited their use."

To get rid of these shortcomings, the scientists decided to use another method, which previously did not lead to the most positive results – the so-called laser ablation, that is, knocking atoms out of the target with a laser beam so that these torn atoms would then join together into a nanocrystal. The problem here was that the torn atoms in this case were most often combined not into particles, but into some disordered layers, and even if nanoparticles were obtained, they did not glow. This happened because either the nanoparticles were too large, or they cooled down too quickly and did not have time to form high-quality nanocrystals. In other words, it was necessary to warm them up to stimulate crystallization, and for a very short time.

"To do this, we decided to use short pulses of high–intensity laser radiation," says Professor Tymoshenko. – They not only knocked atoms out of the silicon target, but also ionized them. The electrons that flew out of them led to the ionization of helium atoms, in the atmosphere of which all this happened. For a very short time, in nanoseconds, something like a microwave appeared, laser plasma conditions were formed, which allowed atoms to sinter into spherical nanoparticles-crystals. These balls fell to the surface, where they were collected in the form of a loose layer, which can then be easily dispersed in water."

These nanoparticles had a spherical shape and were just the size – 2-4 nanometers in diameter – which, as physicists well knew, provides silicon with effective photoluminescence, in which one incident photon accounts for one ejected. Unlike the nanoparticles obtained by chemical etching, they were devoid of toxic additives. And most importantly, as shown by the conducted biological experiments, they could easily penetrate the cells. Moreover, such nanoparticles penetrate into cancer cells much more readily than into healthy ones. This is due to the fact that the cancer cell is always ready to divide, always absorbs everything that is next to it in order to give birth to daughter cells. According to Viktor Tymoshenko, depending on the type of cell, cancer cells usually absorb nanoparticles 20-30% more efficiently than healthy ones, and this can be the basis for the diagnosis of cancer at an early stage of its development.

Cancer cells with laser–illuminated nanoparticles inside them.
Source: Viktor Tymoshenko / Scientific Reports

"The main achievement of our work," says Viktor Tymoshenko, "was that we obtained such nanoparticles and found that they easily penetrate cancer cells. Diagnostic problems are a separate task that is being solved by biologists in parallel, including with our participation. You can, for example, replace a biopsy analysis, which is quite lengthy and not too reliable, with a yes-no test, in which a cancer cell in a tissue sample removed from the body is recognized by whether a nanoparticle has entered it or not. Non-invasive diagnostic methods are also possible. Photoluminescent light emitted by nanoparticles is difficult to use in this case, but they can be activated in other ways, for example, by ultrasound or radio frequency electromagnetic waves."

The nanoparticles obtained by scientists are good because they are completely non-toxic and easily excreted from the body. But their advantage is not limited to this. They are also good because various characteristic substances or groups of biomolecules (for example, antibodies) can be attached to their surface, allowing them to target penetration into cancer cells and thereby increase the effectiveness of diagnostics. According to Viktor Tymoshenko, in the future it will also be possible to attach drug substances to the obtained nanoparticles, which will not only recognize a cancerous tumor, but also conduct local chemo or radiotherapy at the cellular level.

Portal "Eternal youth" http://vechnayamolodost.ru  19.05.2016