Vancomycin conjugated iron oxide nanoparticles for magnetic targeting and efficient capture of Gram-positive and Gram-negative bacteria

Abstract

Drug conjugated iron oxide magnetite (Fe₃O₄) nanoparticles are of great interest in the field of biomedicine. In this study, vancomycin (Van) conjugated magnetite (Fe₃O₄) nanoparticles were envisioned to capture and inhibit the growth of bacteria. Hydrophobic Fe₃O₄ nanoparticles were synthesized by using co-precipitation of ferrous (Fe²⁺) and ferric (Fe³⁺) ions following a surface modification step with oleic acid as stabilizers. Thereafter, a ligand exchange technique was employed to displace oleic acid with hydrophilic dopamine (DOPA) molecules which have a catechol group for anchoring to the iron oxide surface to prepare water dispersible nanoparticles. The surface of the resulting Fe₃O₄/DOPA nanoparticles contains amino (-NH₂) groups that are conjugated with vancomycin <i>via</i> a coupling reaction between the -NH₂ group of dopamine and the -COOH group of vancomycin. The prepared vancomycin conjugated Fe₃O₄/DOPA nanoparticles were named Fe₃O₄/DOPA/Van and exhibited a magnetic response to an external magnetic field due to the presence of magnetite Fe₃O₄ in the core. The Fe₃O₄/DOPA/Van nanoparticles showed bactericidal activity against both Gram positive <i>Bacillus subtilis</i> (<i>B. subtilis</i>) and <i>Streptococcus</i> and Gram-negative bacteria <i>Escherichia coli</i> (<i>E</i>. <i>coli</i>). Maximum inhibition zones of 22 mm, 19 mm and 18 mm were found against <i>B. subtilis</i>, <i>Streptococcus</i> and <i>E. coli</i> respectively. Most importantly, the vancomycin conjugated nanoparticles were effectively bound to the cell wall of the bacteria, promoting bacterial separation and growth inhibition. Therefore, the prepared Fe₃O₄/DOPA/Van nanoparticles can be promising for effective bacterial separation and killing in the dispersion media.