Evaluation of Surface-modified Superparamagnetic Iron Oxide Nanoparticles to Optimize Bacterial Immobilization for Bio-separation with the Least Inhibitory Effect on Microorganism Activity

Background: Magnetic cell immobilization has been introduced as a novel, facile and highly efficient approach for cell separation. A stable attachment between bacterial cell wall with superparamagnetic iron oxide nanoparticles (SPIONs) would enable the microorganisms to be affected by an outer magnetic field. At high concentrations, SPIONs produce reactive oxygen species in cytoplasm, which induce apoptosis or necrosis in microorganisms. Choosing a proper surface coating could cover the defects and increase the efficiency. Methods: In this study, asparagine, APTES, lipo-amino acid and PEG surface modified SPIONs was synthesized by co-precipitation method and characterized by FTIR, TEM, VSM, XRD, DLS techniques. Then, their protective effects against four Gram-positive and Gram-negative bacterial strains including Enterococcus faecalis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were examined through microdilution broth and compared to naked SPION. Results: The evaluation of characterization results showed that functionalization of magnetic nanoparticles could change their MS value, size and surface charges. Also, the microbial analysis revealed that lipo-amino acid coated magnetic nanoparticles has the least adverse effect on microbial strain among tested SPIONs. Conclusion: This study showed lipo-amino acid could be considered as the most protective and even promotive surface coating, which is explained by its optimizing effect on cell penetration and negligible reductive effects on magnetic properties of SPIONs. lipo-amino acid coated magnetic nanoparticles could be used in microbial biotechnology and industrial microbiology.