The development of nanostructures with antibacterial, AB, properties is crucial, especially given the increasing prevalence of antibiotic-resistant bacteria. We developed a straightforward and scalable synthesis of one-dimensional lepidocrocite titanate nanofilaments (1DL NFs). Our method involves reacting titanium precursors (e.g., TiB₂, TiC, TiOSO₄) with tetraalkylammonium hydroxides (TAAH) at ambient pressure and temperatures below 80 °C. The resulting 1DL NFs consist of 2×2 TiO₆ octahedra bundles with cross-sections of about 5×7 Å² and lengths of tens of nanometers. Remarkably, aligning one gram of these filaments end-to-end would extend approximately 700 million kilometers.
In our study, we present the first investigation into the AB activity of 1DL titanate NFs synthesized using TMAOH or ChoOH. To assess the influence of intercalated cations on the AB properties we ion-exchange the original TMA⁺ or Cho⁺ cations present after reaction with potassium (K⁺) or sodium (Na⁺), resulting in K-1DL and Na-1DL variants, respectively.
The AB efficacy of these materials was evaluated against three model bacteria: the Gram-negative Escherichia coli (E. coli) and the Gram-positive Bacillus subtilis (B. subtilis) and Listeria innocua (L. innocua). We examined the antibacterial activity in relation to NF size, incubation duration, and concentration, utilizing both colony-forming unit (CFU) assays and flow cytometry for comprehensive analysis. Using CFU assays, we observed AB activities of approximately 96% for E. coli and 99% for the Gram-positive strains after a 4-hour exposure to light. Flow cytometry analyses indicated that direct physical contact between bacterial cells and 1DL NFs is pivotal for their AB function. Scanning electron microscopy revealed that the AB mechanism mainly involves physical disruption of bacterial membranes, with bacteria becoming trapped or enveloped by the nanometer-thin 1DL NFs, leading to agglomerate formation that can potentially be filtered out. Notably, while reactive oxygen species (ROS) generation has been previously identified as a contributing factor in bacterial elimination by titania, our material demonstrated efficacy exceeding 85% even in the absence of light. This suggests that mechanisms, beyond ROS generation, are at play. These findings position 1DL NFs as a promising new class of AB materials, with potential applications in AB treatments, water purification, and environmental remediation.

Michel W. Barsoum

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