Enhancement Effect of Static Magnetic Field on Bactericidal Activity

The biological effects of magnetic fields are pervasive in microorganisms, with significant attention given to alternating magnetic fields (AMFs). However, AMFs induce electrical and magnetothermal effects, which complicate the interpretation of magnetic field-induced biological effects and introduce uncertainties regarding cytotoxicity in practical applications. The static magnetic field (SMF) with few variables and high biocompatibility presents a promising alternative for both understanding biological mechanisms and ensuring safe applications, but has a remaining problem on weak interactions with microorganisms. Here we show that the combination of SMF with paramagnetic calcium-polypyrrole nanoparticles (Ca-PPy) remarkably enhances bactericidal activity. Our experiments indicate that the synergistic action of SMF and Ca-PPy significantly promotes the generation of reactive oxygen species (ROS), i.e., singlet oxygen and superoxide anion radicals, in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), coupled with the physical disruption of bacterial membrane, exhibiting the extraordinary bactericidal performance (the bactericidal rate is over 94%). The mechanism disclosed by computations is that the singlet-to-triplet transition of radical pairs can be increased by the introduction of magnetic fields. These findings offer new insights into the biological effects of magnetic fields and pave the way for their safe, highly effective use in bactericidal applications.