Evaporation-condensation in the presence of unipolar ionic flow for solvent-free production of ultrasmall antibacterial particles

Because of antibiotic resistance threats, there has been a resurgence of interest in Ag or Cu nanoparticles (NPs) with soft functional components as composite particulates or coatings for broad-spectrum and strong antibacterials despite the biotoxicity of the NPs. Although the composite architectures conferred stimuli-responsive and safer antibacterial functions to the particulates or coatings, the renewal of antibacterial activity for long-term care remains a challenge, and the preparation and storage of the composites require complex and costly chemistries and procedures. Consequently, developing a digitizable platform for the plug-in manufacture of ultrasmall (atomically countable) Ag or Cu particles may represent an important advancement because an on-demand post-processing method for conferring functional overlayers onto NPs was recently introduced. In this study, a tandem electrostatic system consisting of a carbon brush ionizer and a spark ablation device was developed, in which gaseous ions (1 × 10⁷ ions cm⁻³) were injected into the spark ablation passage between Ag or Cu rods to ensure the steady and uniform manufacture of ultrasmall Ag or Cu particles (~3 nm). The resulting Ag or Cu particles exhibited stronger and more stable antibacterial activities against bacteria (including multidrug-resistant strains) than Ag or Cu NPs (>10 nm).