Nanorevolution
What provided quantum dots with a breakthrough in medicine
Modern medicine is already unthinkable without nanotechnology. Scientists are constantly looking for and developing new materials and methods of their application. Nanoparticles smaller than one ten thousandth of the diameter of a human hair – quantum dots – have provided a scientific breakthrough in diagnostics and pharmacology. The National Research Nuclear University "MEPhI" is actively exploring the possibilities of using quantum dots in the field of biomedicine.
Quantum dot (they are also called "artificial atoms") – this is a semiconductor crystal with such a small size that the electrons in it are limited in movement in three dimensions. This is comparable to lying in a box with a ball that can only move between its walls. The term "quantum" in this case implies that the various characteristics of this point, for example optical and electrical, vary depending on its size.
Quantum dots were discovered in the fifties of the twentieth century. For quite a long time they have been a passive object of study of physicists. Then chemists learned how to synthesize quantum dots by setting sizes and thus controlling their physical and chemical properties. But in biology and medicine, quantum dots began to be used only after a way was found to make them soluble in water and biological fluids, as well as to control their size, that is, to set physical properties even in the process of creation.
In medicine, colloidal quantum dots are most often used – nanocrystals obtained by chemical high-temperature synthesis. A composition with the necessary chemical reagents is injected into a heated medium comprising two or more phase states. As a result, a rapid chemical reaction occurs with the formation of solid phase nuclei. These are the foundations for crystal quantum dots. Further, the particles grow, and their size is controlled with an accuracy of up to 10%. The average size of quantum dots suitable for use in medicine is from two and a half to five nanometers. Optical properties depend on the size: when exposed to external radiation, small nanocrystals glow with violet light, and large ones glow with red.
The main obstacle to the introduction of most nanoparticles into the human body is their toxicity to living cells, and not only of one or another chemical element that is part of them. It's about nanotoxicity. Nanoparticles have a very small size, similar to the size of biological molecules. Our own proteins stick to the nanocrystal, turning inside out at the same time, which leads to a sharp reaction of the immune system, which seeks to destroy the "alien" protein.
Nanoparticles can become centers for the formation of filamentous (fibrils) and tangled proteins resembling plaques formed in Alzheimer's disease and capable of blocking the transmission of a nerve impulse. The "attraction" of proteins by nanocrystals is fought in different ways. For example, at the MEPhI Research Institute, they strive to make the surface of the particles as "unattractive" as possible for the adhesion of proteins, as well as to exclude their adhesion. At the same time, the size should be maintained within the established limits (2.5–5 nanometers) so that crystals are excreted from the body with a probability close to 100%.
"Most likely, it will not be possible to completely eliminate the problem of toxicity of nanomaterials. However, the prospects for their use in medicine will always be determined by the balance of negative and positive properties that they can bring to diagnosis and treatment. It is obvious that antitumor drugs pose a serious danger to healthy body tissues, but otherwise the tumor simply cannot be destroyed! Therefore, the task of nanobiotechnologists is to minimize the effects of toxic substances on healthy cells and organs. We have to take a certain risk in order to eventually get more chances to save human life and health," Igor Nabiev, head of the Laboratory of Nano– and Bioengineering at the MEPhI National Research Institute and professor at the University of Reims Champagne-Ardennes (France), told RIA Novosti.
At the moment, a project is being developed at the MEPhI Research Institute for the creation of carriers, including microcapsules charged with medicine, into the walls of which magnetic and silver nanoparticles, as well as radioactive and fluorescent quantum dots are introduced. Thanks to the latter, the capsules glow, which makes it possible to register their location, and the particles are also controlled by a magnet, moving the entire capsule to the location of the tumor. With the help of an alternating magnetic field or ultrasound, they can be heated and opened at the moment when they have reached the target.
It is noteworthy that quantum dots do not "linger" at the research stage: practically applicable specific devices are being actively developed on the basis of nanocrystals. A whole series of devices capable of detecting a large number of pathogens at the same time is being created at the MEPhI Research Institute. These devices will be able to detect a number of infections from just one air sample. The release of a pilot series of such devices is planned in 2019-2020.
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