Bacteria Detection with Interdigitated Microelectrodes: Noise Consideration and Design Optimization

Impedimetric biosensors are promising for label-free, real-time, sensitive and selective detection of bacteria. However, these sensors do typically not detect below 103 colony forming unit (CFU) per ml in absence of dielectrophoresis and labels. This work shows that the noise source due to random distributions of bacteria on the biosensor surface strongly restricts the limit of detection (LOD) for an interdigitated microelectrode (IDE) configuration. 3D finite-element simulations also indicate that the bacteria diameter and the surface coverage influence both the sensitivity and the signal-to-noise ratio (SNR). Optimization of the IDE design suggests that the SNR is maximized, i.e., the LOD is minimized, as the electrode gap is approximately five times the bacteria diameter and the electrode width and thickness are minimized and maximized with regards to current technological limitations, respectively. The paper finally highlights the critical design trade-off between SNR and sensitivity maximization.