Effect of Antimicrobial Nanoparticles on Bacterial Motility in Microfluidic Channels of Varying Geometry and Confinement: Implications for Water Disinfection

Abstract

Water disinfection in packed-bed filter columns can be understood by studying bacterial motion in microgeometries. Microfluidics combined with image analysis provides an ideal platform to probe these dynamics with high spatiotemporal resolution. This study aims to elucidate the effects of copper nanoparticles (CuNPs) on the motility of GFP-tagged E. coli within microfluidic channels, with tunable geometric curvatures and varying confinement, mimicking the granular carbon-matrix characteristics of filter columns. In straight and pillared (portraying aspherical carbon granules) channels of 150 or 20 μm width, the presence of CuNPs reduces bacterial translational diffusivity by two and 3 orders of magnitude, respectively. This was accompanied by a transition from near-ballistic (anomalous diffusion exponent, α ∼ 1.8) to near-diffusive motion (α ∼ 1.2) in straight channels and subdiffusive (α ∼ 0.6) in pillared channels. Simultaneously, there is an increase in rotational motion, as evidenced by higher tumbling frequency and rotational velocity, with pronounced large-angle reorientations (90°–180°). This increase in bacterial rotational motion is interpreted as an escape mechanism from the stress environment induced by CuNPs. Therefore, we conclude that CuNPs in water filter columns alter bacterial motility through both biocidal action and a combination of physical constraints (geometrical curvature and channel confinement).