Photothermally Induced Vapor Nanobubbles Enable Disruption and Antibiotic-Improved Responsiveness in Uropathogenic Biofilms

Treating bacterial biofilms remains a major clinical challenge, particularly in uropathogenic infections where the dense extracellular matrix impedes antibiotic access and protects tolerant bacterial populations. In this work, we explored a nanomaterial-based strategy to improve antibiotic responsiveness by combining iron oxide nanoparticles (IONPs) with pulsed laser irradiation to induce vapor nanobubble (VNB)-mediated disruption of a mature flow-grown uropathogenic E. coli CFT073 biofilm. We tested three nanoparticle sizes (70 nm, 130 nm, and 500 nm) and identified IONP 500 as the most effective formulation for generating VNBs upon irradiation with 532 nm nanosecond laser pulses, with a VNB threshold of 0.56 J/cm 2 per pulse. In the mature biofilm model, the combined IONP 500 + ciprofloxacin + laser treatment significantly enhanced antibiotic activity compared with ciprofloxacin alone, increasing dead biomass from approximately 16% to 23%, corresponding to a 39–45% relative increase, as quantified by COMSTAT analysis and one-way ANOVA with Tukey’s post-hoc test. The combined treatment also reduced total biofilm biomass and increased biofilm porosity by 55.8% compared with ciprofloxacin alone, supporting a mechanism based on VNB-mediated matrix disruption and improved antibiotic access. Overall, these results support the use of photothermally active, biocompatible IONPs as a promising complementary strategy to enhance the efficacy of conventional antibiotics against persistent biofilm-associated infections.