Polymer Corona Architecture Modulates Nanoparticle–Bacteria Interactions and Photothermal Antibacterial Activity of Polydopamine Nanoparticles

The global rise of antimicrobial resistance (AMR) threatens the efficacy of conventional antibiotics and demands new treatment strategies beyond molecular inhibition. Nanomaterials, particularly polydopamine nanoparticles (PDNPs), offer a promising non-antibiotic platform because of their biocompatibility, facile functionalization, and intrinsic photothermal activity, which can enable spatially and temporally controlled bacterial killing. Here, we investigate how bacterial cell envelope structure and polyethylenimine (PEI) corona architecture modulate PDNP–bacteria interactions and influence photothermal antibacterial efficacy. PDNPs were functionalized with branched PEI (bPEI) of varying molecular weights to leverage its high cationic charge density and enhance nanoparticle association with bacterial surfaces. Although PEI-functionalized PDNPs exhibited similar surface zeta potentials across different bPEI molecular weights, their interactions with bacteria and resulting cytotoxic effects were molecular-weight dependent; this effect was more pronounced for Gram-negative Escherichia coli than for Gram-positive Staphylococcus epidermidis . Heat stress further amplified this response, particularly when combined with laser-induced photothermal heating of the nanoparticles. Together, these findings demonstrate that polymer corona architecture and bacterial cell envelope properties jointly govern PDNP–bacteria interactions and photothermal antibacterial activity, providing design principles for nanomaterial-based strategies to combat AMR.