Capacitive biosensing of bacterial cells: Analytical model and numerical simulations

• A complete model of capacitive biosensors with bacteria has been established.
• Poisson–Nernst–Planck equations provide accurate performance estimation.
• Good matching between experiments, simulations and analytical models.
• Capacitive shifts are found to be caused by the high-conductive bacterial cytoplasm.

Impedimetric biosensors with a passivation layer, also called capacitive biosensors, have recently shown great promise towards sensitive, selective and rapid detection of pathogen bacterial cells. However, few studies focus on their modeling, yet critical for the optimization of their sensitivity. To address this issue, we propose a comprehensive framework by developing analytical models and 2D numerical simulations of passivated interdigitated microelectrodes (IDEs) with adherent bacterial cells in electrolyte. While models provide a qualitative and semi-quantitative analysis of the AC impedance spectroscopy based on the system cutoff frequencies, finite element method (FEM) simulations based on Poisson–Nernst–Planck equations enable accurate quantification of the sensitivity to bacteria versus the applied frequency thanks to modeling of complex phenomena such as ion transport, surface and space charges, multi-shell bacterial dielectric properties and sensor topology. These numerical simulations are assessed by experimental results and compared to analytical models.