In Situ Quantification of Bacterial Surface Charge at the Single-Cell Level for Modeling Transport under Electric Fields

Locally enhanced electric field treatment (LEEFT) inactivates bacteria via charge-dependent transport into localized high-field regions, requiring resolution of surface-charge heterogeneity rather than population-averaged zeta potentials. Here, we develop a high-throughput single-cell tracking platform to quantify the effective surface charge at the individual-cell level. Using this approach, we reveal heterogeneity in effective surface charge spanning nearly 2 orders of magnitude under fixed medium conditions (pH 5.8) from -1.0 × 10^-18 to -1.8 × 10^-16 C. The least charged 10% of cells migrate at velocities up to an order of magnitude lower than the population average, while highly charged cells migrate much faster, enabling millimeter-scale transport within seconds. This contrast demonstrates that transport behavior is governed by the full effective charge distribution. While medium chemistry changes the overall charge level, with increasing pH shifting the surface charge from positive to negative values, we also found that the bacteria growth phase strongly modulates the width of the charge distribution. Together, these results not only validate the platform for resolving single-cell effective surface charge under operating electric fields but also provide distribution-resolved parameters that enable more accurate transport modeling and rational optimization of electric-field-based treatment systems.