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

Drug conjugated iron oxide magnetite (Fe 3 O 4 ) nanoparticles are of great interest in the field of biomedicine. In this study, vancomycin (Van) conjugated magnetite (Fe 3 O 4 ) nanoparticles were envisioned to capture and inhibit the growth of bacteria. Hydrophobic Fe 3 O 4 nanoparticles were synthesized by using co-precipitation of ferrous (Fe 2+ ) and ferric (Fe 3+ ) 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 Fe 3 O 4 /DOPA nanoparticles contains amino (-NH 2 ) groups that are conjugated with vancomycin via a coupling reaction between the -NH 2 group of dopamine and the -COOH group of vancomycin. The prepared vancomycin conjugated Fe 3 O 4 /DOPA nanoparticles were named Fe 3 O 4 /DOPA/Van and exhibited a magnetic response to an external magnetic field due to the presence of magnetite Fe 3 O 4 in the core. The Fe 3 O 4 /DOPA/Van nanoparticles showed bactericidal activity against both Gram positive Bacillus subtilis ( B. subtilis ) and Streptococcus and Gram-negative bacteria Escherichia coli ( E . coli ). Maximum inhibition zones of 22 mm, 19 mm and 18 mm were found against B. subtilis , Streptococcus and E. coli 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 Fe 3 O 4 /DOPA/Van nanoparticles can be promising for effective bacterial separation and killing in the dispersion media. (a) The separation of bacteria by vancomycin conjugated Fe 3 O 4 /DOPA/Van nanoparticles and (b) H-bonding interactions between the vancomycin molecule and the d -alanyl- d -alanine dipeptide of the bacterial surface.