Surface Modified Chitosan-Stabilized Selenium Nanoparticles With Differentially Charged Thiol Ligands for...

Surface chemistry is a primary determinant of nanomaterial-microbe interactions and thus a powerful lever for tuning their antibacterial activity. Selenium nanoparticles (SeNPs) stabilized by chitosan (chitosan-stabilized SeNPs [CS-SeNPs]) offer a versatile platform for antibacterial engineering, yet the impact of secondary surface coating on their bioactivity remains underexplored. Here, we introduce a dual-coating strategy, in which CS-SeNPs synthesized by ascorbic-acid reduction of sodium selenite in the presence of chitosan for stabilization and post-functionalized with thiolated ligands bearing cationic (-NMe₃⁺), anionic (-COO-), or neutral (-OH) headgroups for enhanced efficiency. Antibacterial performance was quantified against a Gram-positive strain (Staphylococcus aureus) and a Gram-negative strain (Escherichia coli). Anionic@CS-SeNPs and Neutral@CS-SeNPs showed no inhibition within the tested range, whereas Cationic@CS-SeNPs exhibit strong antibacterial activity (minimum inhibitory concentration [MIC]/minimum bactericidal concentration [MBC]: S. aureus 1/2 µg/mL; E. coli 2.5/20 µg/mL), representing ∼70-fold improvement in MIC compared to unmodified CS-SeNPs for S. aureus. Given this potency, we further evaluated antibiofilm efficacy in mature S. aureus and E. coli biofilms and delineated the mode of action using complementary assays. Data support a multimodal mechanism involving extracellular and intracellular reactive oxygen species (ROS) generation, membrane depolarization, and membrane rupture, consistent with robust bactericidal and antibiofilm outcomes. Preliminary biocompatibility tests indicated low cytotoxicity toward mammalian cells under the conditions studied. These findings establish ligand engineering on polymer-capped SeNPs as a modular route to enhance antibacterial and antibiofilm efficacy against both planktonic and biofilm-embedded pathogens.