ITMO decided to mix liquids in microreactors with light and nanoantennas

Scientists from ITMO University and their colleagues from the Czech Academy of Sciences have proposed a method that can help solve the problem of controlling the mixing speed: they decided to use the so-called radiation pressure, which occurs with the help of light energy. At the same time, a nanoantenna with a thickness of 200 nanometers will interfere. Their study is published in Advanced Science.

From time to time, scientists need to control the process of mixing liquids in vessels so small that a thin needle or even hair will not fit there. At the same time, controlling the diffusion rate of molecules in the so-called microreactors is extremely important for developing new drugs, conducting biological experiments, and even conducting quick tests to detect diseases. Scientists from ITMO University and their colleagues from the Czech Academy of Sciences have proposed solving this problem with the help of light energy.

Currently, biologists, chemists, and pharmacists make extensive use of microreactors, often integrated into miniature plants, which are designed to perform several stages of chemical synthesis of a specific product, the so-called “laboratory on a chip” platforms. These tiny containers with small indentations on the inside can range in size from a few cubic millimeters to several cubic centimeters — no more than a matchbox. However, they allow blood tests, mix microscopic doses of substances to create highly effective drugs, and conduct experiments on cells.

However, there is one problem associated with their work: scientists practically do not control the mixing speed or, from a scientific point of view, the diffusion of liquids and reagents inside such laboratories on a crystal. Scientists from ITMO University and their colleagues from the Czech Academy of Sciences have proposed a method that can help solve this problem: they decided to use the so-called radiation pressure.

At the end of the 19th century, the British scientist James Clerk Maxwell made the assumption that light can put pressure on physical objects. Soon, the Russian scientist Peter Lebedev proved this. Nevertheless, the strength of this interaction is very small, and at that time no one found any use in this. Currently, there is a whole field of science called optomechanics that focuses on this phenomenon, and in 2018, the Nobel Prize was awarded to Professor Arthur Eshkin for his innovative work in this field. Light is used to capture living cells and move tiny particles of matter. Now it turns out that the same forces can be used to mix liquids.

“Our nanoantenna turns circularly polarized light into an optical vortex, and the light energy revolves around it”.

Alexander Shalin, Professor, Department of Physics, ITMO

Based on the latest discoveries in the field of optomechanics, scientists from St. Petersburg have developed a nanoantenna consisting of a tiny silicon cube about 200 nanometers in size. This device, invisible to the human eye, can effectively affect light in a special way.

In addition to nanoantennas, scientists also proposed introducing gold nanoparticles into a liquid. Particles captured by the optical vortex begin to rotate around the cube of silicon, acting as a mixing “spoon” for mixing the reagents. Moreover, the size of such a system is so small that it can enhance diffusion in one corner of the microreactor hundreds of times, practically without affecting what is happening in the other.

Liquid mixer

“Gold is a chemically inert material that does not react much. It is also non-toxic. Moreover, we needed to design it so that only nanoparticles and radiation pressure act on the nanoparticles so that other forces do not force them to reach the antenna, otherwise the particles would simply stick to it. This effect is observed for particles of gold of a certain size if we illuminate the system with a conventional green laser. We examined the use of other metals, but for silver, for example, such an effect is observed only in the ultraviolet range, which is less convenient, but maybe useful to increase the efficiency of some photochemically activated reactions”.

Adrianos Valero, one of the main authors of the study

By the way, this method can be used not only for mixing liquids but also for sorting gold nanoparticles: if scientists need to choose gold particles of a certain size, for example, 30 nanometers, for an experiment. To date, the system is fully designed, and a theoretical model has been developed for it. Conducting experiments will be the next step.

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