Silver nanoparticles with pH induced surface charge switchable properties for antibacterial and antibiofilm applications.

Silver nanoparticles (AgNPs) are widely used as antibacterial agents because of their significant antimicrobial activities and little sign of antimicrobial resistance. However, the relatively high toxicity to healthy cells and low penetration efficiency into bacterial biofilms prevent their further use in biomedical applications. In order to decrease the cytotoxicity of the AgNPs to mammalian cells while increasing their antibacterial and antibiofilm efficiency, a novel nanocomposite composed of AgNPs decorated with carboxyl betaine groups (AgNPs-LA-OB) was prepared. The zwitterion modified AgNPs showed a pH responsive transition from a negative charge to a positive charge, which enabled the AgNPs to be compatible with mammalian cells and red blood cells (RBCs) in healthy tissues (pH ∼ 7.4), while strongly adhering quickly to negatively charged bacterial surfaces at infectious sites (pH ∼ 5.5) based on electrostatic attraction. The AgNPs penetrated deeply into bacterial biofilms and killed the bacteria living in an acidic environment. The results indicated that the designed zwitterion NPs for antibacterial applications and eradication of bacterial biofilms, which also had particles that did not harm the healthy cells showed promise for future use in humans. The satisfactory selectivity for bacteria compared to RBCs, together with their potent eradication of bacterial biofilms make AgNPs-LA-OB a promising antibacterial nanomedicine in biomedical fields.