Scientists from ITMO University have developed a production method for bio-integrated optical nanomaterials based on Mie-resonant silicon nanoparticles. The nanoparticles used in the work are covered by biopolymer shells and can be controlled by heat. With light irradiation, the particles change their shape and color. The discovery is poised to support nanophotonic and nanomedicine applications and the development of noninvasive biosensors, signal systems, and nontoxic dyes. Though the issue of controlled nanomaterials is resolved, existing systems that rely on them can be toxic to living organisms, which limits the scope of their application in medicine and biology. The ITMO researchers’ material is fully biocompatible, with controllable properties. “The nanoparticles are composed of silicon cores and biopolymer shells,” said Anna Nikitina, a staff member at ITMO’s Infochemistry Scientific Center. “The substances that make up the shells possess different hydrophobic/hydrophilic qualities, i.e., the way in which their molecules react to water. We were able to use that to make the particles contract or expand depending on external factors.” Hydrophobic materials are those that repel water. Hydrophilic materials are wetted by and absorb water. Because the nanoparticles change both their shape and color under thermal influences, they can be used, for example, to perform noninvasive local temperature measurements in biological tissue or to design sensor systems that can be used to analyze internal processes in living organisms. The nanoparticles can also be used as components of controllable systems that can be used to create thermo- and light-controlled dyes such as the liquid-crystal modulators used in holography and lithography. A team from ITMO University developed a production method for nanoparticles that are composed of silicon cores and biopolymer shells. The substances that make up the shells possess different hydrophobic/hydrophilic qualities. Courtesy of CC0 Public Domain. Changes in the color of the particles occur due to structural transformations, and the controlled particles do not need to be paired with additional complex devices, such as ultrasensitive spectral sensors to collect data from within an organism, said Valentin Milichko, a staff member at ITMO University’s School of Physics and Engineering. “A simple change in color allows us to easily monitor what is happening to the particle in real time. The technology is multiuse, too. Each particle can be turned on and off several times,” Milichko said. The researchers have been developing these controlled systems for three years; they previously experimented with various sizes and spatial characteristics of the nanoparticles, and they searched for polymers that would exhibit the desired performance. The systems’ efficiency has been confirmed only in laboratory conditions. The next step in the study will be in vitro testing, the researchers said. The research was published in Angewandte Chemie (www.doi.org/10.1002/anie.202101188).