Synthesis, characterization and evaluation of biological activities of manganese-doped zinc oxide nanoparticles

Purpose: To synthesize, characterize and investigate the antimicrobial properties of pure and manganese-doped zinc oxide nanoparticles. Method: Un-doped and manganese-doped zinc oxide (Mn-doped ZnO) nanoparticles were prepared using co-precipitation method. The synthesized Mn-doped ZnO nanoparticles were characterized using energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), and x-ray diffraction (XRD) spectroscopic techniques. Their band gap energies were measured with ultraviolet-visible (UV- Vis) spectroscopy, while their antioxidant properties were evaluated by ferric reducing antioxidant power (FRAP), DPPH radical-scavenging, ferric thiocyanate (FTC) and total phenolic content (TPC) assays. The antimicrobial activities of the nanoparticles against different bacterial strains were determined using agar diffusion method. Result: Results from XRD, SEM, EDX and UV-Vis analyses demonstrated successful synthesis of un-doped and Mn-doped ZnO nanoparticles as seen in their hexagonal, wurtzite structures. The un-doped and Mn-doped ZnO nanoparticles had average grain sizes of 16.72 nm and 17.5 nm, and band gap energies of 3.585 eV and 2.737 eV, respectively. Significant antibacterial activity was manifested by Mn-doped ZnO against E. coli, S. aureus, Klebsiella and B. subtilis, with zones of inhibition (ZOIs) of 13 +/- 0.09 mm, 14 +/- 0.01 mm, 18 +/- 0.07 mm and 20 +/- 0.10 mm, respectively. The Mn-doped ZnO nanoparticles also exhibited effective and significant antioxidant potential relative to butylated hydroxytoluene (BHT) and un-doped ZnO nanoparticles. Conclusion: Mn-doped ZnO nanoparticles demonstrate significant antimicrobial and antioxidant activities. Thus, the preparation is a good candidate for further development into therapeutic formulations.