Over the last two years, the COVID-19 pandemic has given rise to numerous projects focused on the development of substances and products capable of inactivating the novel coronavirus. One standout candidate is semiconductors, best known for their applications in industry, especially in electronic devices and car components. Two recent theoretical studies by researchers associated with the Center for the Development of Functional Materials (CDMF), one of the Research, Innovation, and Dissemination Centers (RIDCs) funded by FAPESP, showed the virucidal potential of semiconductors.
One of the studies, carried out by Jeziel Rodrigues Santos during his chemistry PhD at the Federal University of São Carlos (UFSCar), investigated how silicon nanotubes affect SARS-CoV-2. The other, a postdoctoral project at the same institution by engineer Leandro Silva Rosa Rocha, focused on how cerium oxide nanoparticles, known as nanoceria, might be able to combat the novel coronavirus.
Semiconductors usually affect pathogens through oxidation reactions, explains Elson Longo, director of the CDMF and professor emeritus at UFSCar’s Chemistry Department. “We usually eliminate pathogens organically using antibiotics. But they can mutate and become resistant,” says the chemist. “Now, we are pursuing the inorganic chemistry approach, using oxygen and water.”
Longo explains that the semiconductor material interacts with oxygen in the air to form a negative ion and then decomposes water molecules present in the air in the form of water vapor, leading to the formation of a highly oxidizing hydroxyl radical and a proton. This proton interacts with the oxygen, forming a peroxyl radical. Hydroxyl and peroxyl radicals degrade the surface of the virus or bacteria by oxidation, “burning” the protective membrane and inactivating the microorganism. “It’s the same principle as using hydrogen peroxide on a wound to kill bacteria,” summarizes the CDMF director.
The results of the study on silicon nanotubes were published in the Journal of Biomolecular Structure & dynamics. According to Santos, nanotube silicons have the potential to bind to amino acids in the coronavirus spike protein. The structural and electronic properties of the material were theoretically demonstrated by a computer simulation.
“The nanotube structure has a larger contact surface, which helps it interact with the virus membrane,” explains the scientist. The research was carried out in partnership with the State University of Goiás (UEG) and the Federal Institute of São Paulo (IFSP).
The antiviral properties of silica combined with silver, says Santos, were already known. CDMF spinoff company Nanox sells fabrics, leather, and PVC films treated with this combination. According to Longo, silica is a semiconductor that generates molecules with high oxidizing power when activated with metallic silver, making it capable of inactivating 99.9% of the novel coronavirus within 15 minutes.
The antiviral properties of silicon nanotubes still need to be measured. “There is literature on the use of this material for storing energy, carrying drugs, and catalytic processes, but nothing on its antiviral capacities,” says Santos. “The results of our work could contribute to our understanding of the material virucidal potential and pharmacological application.”
In the cerium oxide study, the researchers started with a hypothesis proposed in the article “Nanoceria as a possible agent for the management of COVID-19,” published by a group from India in the journal Nano Today in 2020. Rocha was studying another possible application of cerium oxide: as a gas sensor, a method already used in glass and mirror polishing, among other industrial uses.
When the pandemic began, he redirected his research toward combating SARS-CoV-2. The first step was to synthesize the material. For the study, the results of which were published in the journal Scientific Reports in February, cerium oxide was prepared as a hybrid material containing a polymer matrix of microcrystalline cellulose to enable it to be applied on surfaces and potentially administered in vivo. “Cerium oxide nanoparticles in their free form are toxic to our body. Encapsulated in the polymer matrix, however, their toxicity can be nullified,” explains the researcher.
The study detected the presence of defects in the material’s structure that are necessary for it to have a virucidal effect. These structural defects are imperfections in the regular arrangement of the atoms due to ion vacancies or voids. “To compensate for the defect, the material reacts with the surface of the virus and inactivates it during this interaction.” The scientific literature indicates that the phenomenon observed with nanoceria also occurs with nanotubes.
The next step in the nanoceria research is to prove its antiviral activity. This stage is scheduled to begin in June, in parallel with new spectroscopy studies, which will reveal more data on the structure and properties of nanoceria.
Raluca Savu, a physical engineer from the Center for Semiconductor Components and Nanotechnologies at the University of Campinas (CCSNano-UNICAMP), sees the research carried out at CDMF as part of the quest to find complementary solutions to existing medical and pharmaceutical resources to combat pandemics. In 2020, Savu directed her studies of graphene oxide toward the development of face masks in collaboration with Ljubica Tasic, a chemist from the Institute of Chemistry at UNICAMP.
Their partnership resulted in a more sustainable production process for antiviral silver nanoparticles to be used in sprays, packaging, and mask filters made of cellulose nanofibers and graphene oxide. “To produce the nanoparticles, we use a polyphenol, an organic compound extracted from oranges, as a reducing agent,” explains Tasic. The pair have filed a patent application for their nanoparticle production process and are now looking for partnerships to begin commercial production.
In-depth spectroscopic investigations of hybrid cerium oxide quantum-dots for mitigating the COVID-19 pandemic (nº 20/02352-5); Grant Mechanism Postdoctoral fellowship abroad; Supervisor Elson Longo da Silva (UFSCar); Grant Beneficiary Leandro Silva Rosa Rocha; Investment R$172,758.89.
MENDONÇA, P. S. S. et al. Single-walled silicon nanotube as an exceptional candidate to eliminate SARS-CoV-2: A theoretical study. Journal of Biomolecular Structure and Dynamics. feb. 2022.
ROCHA, L. S. R. et al. Synthesis and defect characterization of hybrid ceria nanostructures as a possible novel therapeutic material towards COVID-19 mitigation. Scientifc Reports. feb. 2022.
ALLAWADHI, P. et al. Nanoceria as a possible agent for the management of Covid-19. Nano Today. dec. 2020.