Influence of Ligand Functionalization on the Synthesis of Metallic-Decorated Magnetic Nanoparticles for Antibacterial...

The inherent magnetism of iron oxide nanoparticles (IONPs) provides appealing benefits for antibacterial treatment, as IONPs can be readily guided, concentrated, and removed from a specific site. Additionally, gold and silver demonstrate antibacterial properties that effectively inhibit bacterial growth. By combining one of these antibacterial metals and the IONP, a dual-purpose metallic nanoparticle treatment can thus be constructed. In our study, we developed silica-coated IONPs to facilitate the binding and decoration with either gold (Au) or silver (Ag). Therefore, the focus of this research is to apply the hard/soft acid/base (HSAB) theory by investigating the affinity of Au or Ag after encapsulating the IONPs with one of three silane capping agents, providing either an amine (AP-SIONP), hydroxide (T-SIONP), or thiol (MP-SIONP). With the use of inductively coupled plasma optical emission spectroscopy (ICP-OES), the amount of metal decorated on the antibacterial metallic SIONPs was compared. We demonstrated that although both Au and Ag had an affinity for all three ligands, Au (79 ± 18 and 23 ± 0 μg/L) and Ag (72 ± 36 and 160 ± 23 μg/L) had a higher affinity for amines and thiols, respectively. Finally, the optimal Au and Ag SIONPs were applied to a Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterium to investigate their antibacterial and capturing potential. Our findings indicate that AgMP-SIONPs demonstrated superior antibacterial potential by providing inhibitory concentrations at 62.5 and 500 μg/mL for E. coli and S. aureus, respectively. Moreover, AgMP-SIONPs provided a minimum bacterial concentration (MBC) at 62.5 μg/L but did not reach MBC for the Gram-positive bacterium. Overall, this study provides the protocol for an optimal antibacterial metallic SIONP through the application of the HSAB theory and demonstrated the promise of silver for its antibacterial potential and SIONP ability to further capture bacteria, all of which opens a promising research exploration.