Robust antibacterial activity of rare-earth ions on planktonic and biofilm bacteria.

Bacterial infections pose a serious threat to human health, with emerging antibiotic resistance, necessitating the development of new antibacterial agents. Cu ²⁺ and Ag ⁺ are widely recognized antibacterial agents with a low propensity for inducing bacterial resistance; however, their considerable cytotoxicity constrains their clinical applications. Rare-earth ions, owing to their unique electronic layer structure, hold promise as promising alternatives. However, their antibacterial efficacy and biocompatibility relative to conventional antibacterial agents remain underexplored, and the variations in activity across different rare-earth ions remain unclear. Here, we systematically evaluate the antibacterial activity of five rare-earth ions (Yb ³⁺ , Gd ³⁺ , Sm ³⁺ , Tb ³⁺ , and La ³⁺ ) against Staphylococcus aureus and Pseudomonas aeruginosa , benchmarked against well-established antibacterial agents (Cu ²⁺ , Ag ⁺ ) and the antibiotic norfloxacin. Cytotoxicity is also assessed via live/dead staining of fibroblasts after 24 h rare-earth ion exposure. Our findings reveal that rare-earth ions require higher concentrations to match the antibacterial effects of traditional agents but offer the advantage of significantly lower cytotoxicity. In particular, Gd ³⁺ demonstrates potent bactericidal efficacy against both planktonic and biofilm bacteria, while maintaining the lowest cytotoxicity toward mammalian cells. Moreover, the tested rare-earth ions also exhibited excellent antifungal activity against Candida albicans . This study provides a critical empirical framework to guide the selection of rare-earth ions for biomedical applications, offering a strategic direction for the development of novel antimicrobial agents.
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