Aumento da atividade bactericida e virucida de partículas e de filmes compósitos de cobre sob influência de luz branca

Abstract

In light of the pandemic caused by the novel coronavirus (SARS-CoV-2) in late 2019, research into virucidal materials has accelerated. Additionally, with the rise of antibiotic-resistant microorganisms and the constant healthcare-associated infections, the interest in the development of bactericidal materials and surfaces is also rising. Copper (Cu) stands out in this field due to its intrinsic biocidal properties. Moreover, copper?s ability to absorb visible light makes it a photoactive material, a characteristic that has not been extensively studied or reported in the literature. To fill this gap, the present study evaluated the bactericidal properties of suspensions of metallic copper particles at both micro (CuMPs) and nanoscale (CuNPs), as well as copper (I) oxide microparticles (Cu2OMPs), under dark and white light illumination conditions against Staphylococcus aureus and Escherichia coli. The particles were subsequently incorporated into a polyvinyl alcohol (PVA) matrix to obtain composite films, which were tested against the same bacterial strains and the enveloped murine hepatitis virus type 3 (MHV-3) under both illumination conditions. UV-Vis spectroscopy confirmed that all particles exhibit a band gap in the visible region. XRD, FTIR, and Raman analyses did not detect contamination or oxidization, though XPS revealed partial oxidation on the surfaces of the particles. Microscopic analysis showed average sizes of 7.7 ± 5.6 (mi)m for CuMPs and 7.6 ± 3.9 (mi)m for Cu2OMPs, while CuNPs measured approximately 43 ± 12 nm. The bactericidal photoactivity against S. aureus for CuMPs and Cu2OMPs suspensions at a concentration of 2.5 mg mL-1 was significantly enhanced under visible light, achieving a 7 log reduction, with increases of 66% and 37% (p < 0.05), respectively, compared to dark conditions. These findings suggest that the photoactivity of these materials is dose-dependent. For the CuNPs suspension at the same concentration, the nanoparticulate material demonstrated superior performance, indicating that copper bactericidal action is also size-dependent. Against E. coli, CuNPs exhibited the highest activity, followed by Cu2OMPs, which at a concentration of 5 mg mL-1 reduced the bacterial load by 3 logarithmic units under both illumination conditions. The 10 mg mL-1 CuMP suspension displayed a substantial increase, achieving a logarithmic reduction from 3 to 8 log under illumination (p < 0.001), indicating a 167% higher activity. After confirming the photoactivity of the copper particles, composite films were synthesized by incorporating 2% w/v of the particles by the drop casting technique. Over a 24-hour exposure period, the films demonstrated a 6 log reduction in bacterial load (over 99.9999% reduction) against both S. aureus and E. coli, showing impressive results without significant differences between illumination conditions. In tests against the MHV-3 virus, using mouse fibroblast line L929, only the film containing CuMPs under illuminated conditions showed no cytopathic effect, indicating virucidal photoactivity. The ICC-RT-qPCR assay revealed that the composite film reduced viral load by 43.1% when exposed to white light, while the reduction in dark conditions was only about 6.8%. These findings demonstrate the successful synthesis of photoactive composite films using relatively low-cost copper microparticles and a conventional deposition method. The promising results highlight the potential of materials and surfaces with photocatalytic properties activated by visible light to combat the spread of pathogens, supporting further research and development in this field. [resumo fornecido pelo autor]