Synthesis, characterization and antimicrobial studies of manganese (II) and europium (III) metal ion doped zinc oxide nanoparticles for potential clinical applications

Zinc oxide (ZnO) nanomaterials have a unique set of properties making them desirable for a variety of industrial applications including optical, electronic and biomedical technology. Our research is focused on enhancing the antimicrobial activity of ZnO nanoparticles. Our previous research used a precipitation method for making ZnO nanoparticles with manganese doping and subsequently, the particles were introduced into cotton fabric for possible clinical use. However, these particles lacked monodispersity and after three washes, the cotton fabric no longer possessed the antimicrobial properties. The following research proposes a comparative study of synthetic methods by developing a selective precipitation method for manganese (II) doped ZnO nanoparticles and adapting a literature precipitation method for europium (III) doped ZnO nanoparticles. Herein, the purpose of the research is focused on doping ZnO nanoparticles with Mn2+ and Eu3+ metal ions to explore the effects of metal ion doping and the particle size on the electronic structure and antimicrobial properties. The nanoparticles were characterized using absorption and luminescence spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), diffuse reflectance spectroscopy, and inductively coupled plasma-optical emission spectroscopy (ICP-OES). Nanoparticle attachment to cotton was performed using two methods, a literature attachment method using 2-propanol, and a collaborative cotton modification method using beta-cyclodextrin as a crosslinker. Antimicrobial activity of the metal-doped nanoparticles was evaluated using two antimicrobial susceptibility testing techniques: agar diffusion and minimum inhibitory concentration (MIC) against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Staphylococcus epidermidis (S. epidermidis). 5% Eu3+ doped ZnO (E5) nanoparticles demonstrated the lowest MIC across all three bacterial species resulting in an MIC value range of 1.25 -- 0.625 mg/mL, 2.50 -- 1.25 mg/mL, and 0.625 -- 0.313 mg/mL for E. coli, S. aureus and S. epidermidis, respectively. Agar diffusion and time-dependent studies evaluated the nanoparticle attachment to cotton textiles against S. aureus bacteria species. Time-dependent testing showed that antimicrobial activity was retained even after three washes for nanoparticles attached to the modified cotton, improving upon our previous research.