Physicists have synthesized composite nanoparticles for theranostics.

The study was published in the journal Nanomaterials. Composite nanoparticles are nanomaterials made up of two or more components. Their properties are determined by the chemical and physical nature of their constituent structures. They have a wide range of applications, from electronics and catalysis to medicine. The potential for medical applications of such particles is linked to their heating under the influence of infrared radiation, which is transparent to biological tissues and living organisms. The development of composite nanoparticles with tunable optical properties is one of the current challenges. Researchers have proposed a new approach to synthesizing MoS₂-Au nanocomposites using femtosecond laser ablation in liquid to achieve tunable optical properties in the near-infrared region.

“The eco-friendliness of the nanoparticle synthesis method using laser ablation in liquid involves several aspects: firstly, we do not use chemical reagents to create the composites, as the synthesis occurs in water. Secondly, we do not need to dispose of reaction products since we act on a solid target of the required material with a laser, 'shedding' nanoparticles from it. Thirdly, the resulting nanoparticles are ligand-free, meaning the absence of a chemical precursor contributes to the cleanliness of their surface,” explained Alexey Bolshakov, director of the Center for Photonics and Two-Dimensional Materials at MIPT.

The nanoparticle solution was synthesized using the method of femtosecond laser ablation in liquid. Laser ablation is a technique that involves impacting a material with high-energy laser radiation. Under the influence of laser radiation, the solid body of the sample becomes plasma, which enters the liquid. Bubbles form within the plasma, where the plasma condenses into nanoparticles. Femtosecond laser pulses initiate rapid and targeted heating of the material, accelerating particle formation and making the synthesis process more efficient. Through a multi-stage process of laser ablation, researchers created nanoparticles with various structures.

“With laser ablation, we can design numerous synthesis protocols by altering the stages of ablation (ablating one material in the solution of another, as well as fragmenting and breaking mixtures of the obtained nanoparticles to create composite nanoparticles). We can also initiate the decomposition of reagents traditionally used for chemical nanoparticle synthesis through laser action. For instance, we can add AgNO₃ to the traditional ablation process and reduce it to silver satellites located on the surface of the particles,” said Ilya Zavidovsky, senior researcher at the laboratory of controlled optical nanostructures at the Center for Photonics and Two-Dimensional Materials at MIPT.

By using one-, two-, and three-step synthesis techniques, scientists obtained composite nanoparticles with a unique "core-shell" and "core-shell-satellite" architecture, combining MoS₂/MoS_xO_y, MoS_xO_y/Au, and MoS₂/MoS_xO_y/Au phases. Physicists studied the properties of the obtained nanoparticles using methods such as Raman spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and optical absorption spectroscopy. Optical spectroscopy of the nanoparticle solutions showed significant changes in the optical response of the particles depending on their structure. Hybrid nanoparticles demonstrated improved photothermal properties under laser irradiation in the near-infrared range. Such particles have potential advantages for selective photothermal therapy.

“We found that during the ablation of MoS₂, a shell of MoO₃ oxide or MoS_xO_y sulfoxide forms on it. It turned out that molybdenum oxide has an absorption peak in the region close to the biological transparency window of tissues, which motivated us to further explore photon heating with an IR laser at a wavelength of 830 nm,” shared Ilya Martynov, senior researcher at the laboratory of two-dimensional materials and nanostructures at the Center for Photonics and Two-Dimensional Materials at MIPT.

It can be said that the developed nanoparticles pave the way for personalized therapeutic applications and are promising candidates for nanophotonics applications and cancer treatment. The method of femtosecond laser ablation not only facilitates the eco-friendly synthesis of Au/MoS₂ hybrids but also allows precise tuning of the optical properties of these nanoparticles.

The work involved scientists from MIPT, the Institute of Engineering Physics for Biomedicine (MEPhI), the Center for New Technologies Research (XPANCEO, UAE), Aix-Marseille University (France), St. Petersburg Academic University of the Russian Academy of Sciences, St. Petersburg State University, and Skoltech. The research was conducted with the support of the Ministry of Science and Higher Education of Russia.