Nanolasers for oncologists

With the participation of Siberian scientists, the world's smallest lasers effective against cancer have been developed

Julia Pozdnyakova, SB RAS
"Open Science"

A group of American and Russian scientists have created the smallest plasmon nanolasers (spasers) that will find application in the diagnosis and treatment of oncological diseases. The results of the work are published in Nature Communications (Galanzha et al., Spaser as a biological probe).

Researchers from Arkansas University of Medical Sciences (USA), Institute of Automation and Electrometry SB RAS, Institute of Inorganic Chemistry named after A.V. Nikolaev SB RAS and The University of Georgia (USA) has developed the smallest 22-nanometer spaser capable of generating coherent optical radiation directly inside living cells and tissues of the body. It is proposed to be used as an ultra-bright water-soluble biologically compatible probe.

This plasmon nanolaser consists of several components: a resonator, which is a gold particle that supports plasmon resonance, and an isoionic isoporous shell filled with a dye (in this case, uranium, it emits in the region of 520 – 530 nanometers, which coincides with the plasmon resonance of a gold nanoparticle, it is well soluble in water and saline, thanks to which is widely used in medicine). Folic acid is "sewn" to the shell – thus the spaser acquires molecular targeting for cancer cells and does not interact with healthy ones.

When these plasma nanolasers are injected into the body, they first accumulate singly or in small groups at the border of the cancer cell membrane. And then, after a ten-minute exposure, they penetrate into the cytoplasm. At the same time, they heat up, and it becomes easy to visualize them using various optical methods.

"We have demonstrated the generation mode associated with the formation of a dynamic nanobubble around this spaser, which leads to a giant laser effect with a radiation intensity 100 times greater and a spectral width 30 times narrower than for quantum dots," says Alexander, Doctor of Physico–Mathematical Sciences, head of the Laser Physics laboratory at the Institute of Automation and Electrometry SB RAS Ivanovich Plekhanov.

A drawing from an article in Nature Communications – VM.

Spasers can not only visualize cancer cells, but also kill them. When the threshold of radiation generation is significantly exceeded, due to the fact that the metal core absorbs it, a vapor nanobubble forms around the plasmon, which destroys the dangerous cell – first the cytoplasm, then the membrane. Moreover, all this works at energies even lower than required by laser safety standards.

"We studied the cytotoxicity of our spazers in a solution with breast cancer cells and found out that their content up to 10 milligrams per milliliter of solution (much less is needed to achieve a therapeutic effect) is not dangerous," the researcher comments. – That is, when spasers enter a cancer cell, they do not kill it. But if exposed to laser radiation, it dies – due to the fact that the resulting structure breaks the cancer cell from the inside. At the same time, they do not react to a normal cell, regardless of whether there is laser radiation there or not."

The diagnostic potential of spasers has been demonstrated both in experiments with a solution of cancer cells and in experiments on mice – marked cancer cells in blood and lymph currents are clearly visible through living tissue.

"Thus, we demonstrated the universal functionality of spasers in various biological conditions (cell cytoplasmas, test tubes, mouse tissues in vivo) and established that spasers can serve as low-toxic probes with molecular specificity and high spectral brightness, which cannot be achieved using quantum dots. It was possible to show the effectiveness of plasmon nanolasers as photothermal and photoacoustic contrast diagnostic and therapy tools," says Alexander Plekhanov.

Now researchers are working to make a spaser that would work in the infrared region. Then it will be possible to improve some indicators, such as transparency of fabrics.

Portal "Eternal youth" http://vechnayamolodost.ru  13.06.2017