Much progress has been achieved in the preparation and application of engineered nanoparticles (NPs) in the field of medicine, mainly for antibacterial and antiviral applications. In the war against bacteria and viruses, besides traditional antibiotics and antiviral drugs, metal-based nanoparticles, such as silver (AgNPs), copper (CuNPs), copper oxides (CuO-NPs), iron oxide (FeO-NPs), zinc oxide (ZnO-NPs), and titanium oxide (TiO₂-NPs) have been used as potent antimicrobial agents. These nanoparticles can be synthesized by traditional methods, such as chemical and physical routes, or more recently by biogenic processes. A great variety of macro and microorganisms can be successfully used as reducing agents of metal salt precursors in the biogenic synthesis of metal-based NPs for antimicrobial activity. Depending on the nature of the biological agent, NPs with different sizes, aggregation states, morphology, surface coatings and charges can be obtained, leading to different antimicrobial effects. Considering the drug resistance to traditional therapies, the development of versatile nanomaterials with potent antimicrobial effects is under intensive investigation. In this sense, this review presents and discusses the recent progress in the preparation and application of metal-based nanoparticles biogenically synthesized for antibacterial and antivirus applications. The strength and limitations are critically discussed.

This study aimed to evaluate the toxicity of superparamagnetic iron oxide nanoparticles (SPIONs) synthesized by biogenic (BS) and chemical (CH) routes. The nanoparticles were characterized by X-ray diffraction (XRD), X-ray spectroscopy (XPS), atomic force microscopy (AFM), vibrating-sample magnetometry (VSM-SQUID), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The toxicity of SPIONs was evaluated using Artemia salina as model aquatic organisms and Raphanus sativus and Lactuca sativa as model plants to evaluate their phytotoxicity. The results obtained from XRD, XPS, and AFM confirmed the formation of spherical nanoparticles of 41.9 ± 1.00 nm (BS route) and 19.8 ± 0.47 nm (CH route). VSM-SQUID demonstrated the superparamagnetic behavior of both nanoparticles, and FT-IR provided evidence of the differences in the surface of SPIONs, suggesting the presence of phenolic compounds on the surface of BS-SPIONs. For the assays with Artemia salina, the results demonstrated (i) nonsignificant differences of BS-SPIONs in mortality rates, and (ii) significant toxicity (p < 0.05) was observed for CH-SPIONs at 300 and 400 mg L⁻¹. The Raphanus sativa plant assay tests showed (i) BS-SPIONs and CH-SPIONs improved the root elongation of seedlings. However, BS-SPIONs demonstrated significant activity on root seedling elongation (p < 0.05) in the range of 300 mg L⁻¹ to 600 mg L⁻¹. To the best of our knowledge, this is the first report to compare the toxicity of chemically and biogenically synthesized SPIONs. In conclusion, although BS-SPIONs and CH-SPIONs present similar structures, their characteristics of magnetic saturation and surface structure are nonidentical, providing differences in their biological activity.

Iron oxide magnetic nanoparticles (Fe₃O₄ NPs) are used to drive and to promote sustained release of drugs in target sites. Biocompatibility and superparamagnetic behaviour are important features to the successful biomedical applications of Fe₃O₄ NPs. In this study, Fe₃O₄ NPs were synthesized by the co-precipitation method and coated with chitosan (CS) containing ascorbic acid (AA), allowing formation of Fe₃O₄@CS-AA NPs. The antioxidant AA was used as a drug model. The synthesized NPs were characterized by different techniques. The results showed the formation of spherical nanoparticles with average diameter of 67.22 ± 0.82 nm, at solid state, as analysed by atomic force microscopy (AFM). The NPs were found to have a superparamagnetic behaviour at room temperature, and the presence of CS-AA on the surface of Fe₃O₄ NPs did not affect the superparamagnetic behaviour of the nanoparticles. The in vitro AA release assay showed a sustained release of the model drug from Fe₃O₄@CS-AA NPs for at least 48 h. In addition, cytotoxicity assays for Fe₃O₄ NPs and Fe₃O₄@CS-AA NPs did not show significant toxicity towards mammary epithelium (MCF-10A) cell line after 24 h of incubation. This present study demonstrated the successful synthesis of superparamagnetic and biocompatible Fe₃O₄@CS-AA NPs, which are able to release the model drug in a sustained manner. Thus, this nanomaterial might act as a nanocarrier in target drug release.

Zinc is an important nutrient for several plants and humans. Nitric oxide (NO) is a free radical that is important to biological processes that mediate the growth and mitigation of biotic and abiotic stresses in plants. The present study investigated the enzymatic and photosynthetic profile and the accumulation of macro- and microelements in rice plants (Oryza sativa L.) that received foliar treatments of zinc oxide nanoparticles (ZnO NPs), nitric oxide donor (GSNO), and the association of both (GSNO–ZnO NPs). Zinc concentration in rice husks increased by 66% and 68% in plants treated with ZnO NPs and GSNO–ZnO NPs, respectively. The GSNO treatment caused an increase of 25% in the Fe concentration in the rice grains. Only a small disturbance of the antioxidant system was observed, with increases in H₂O₂, S-NO, and NO₂⁻, mainly in the group treated with GSNO–ZnO NPs; however, the disturbance did not affect the yield, the growth, or vital processes, such as as photosynthetic pigments production. There was an increase in chlorophyll B of 290% and an increase in chlorophyll A of 187% when ZnO NPs was applied. GSNO–ZnO NPs increased chlorophyll B by 345% and chlorophyll A by 345%, indicating that the treatments GSNO, ZnO NPs, and GSNO–ZnO NPs reduced possible oxidative stress and helped as protective treatments.