In Situ Electrochemical Monitoring of <i>Bacillus cereus</i> Biofilm Formation

Unwanted biofilms pose significant challenges in the food industry, on medical devices, in water supply systems and marine environments, and even in space exploration. Label-free, advanced sensing approaches such as electrical impedance spectroscopy (EIS) have been investigated as tools for monitoring biofilm formation. The electrode material and the surrounding medium, differing in carbon source, ionic strength, or nutrient availability, can strongly influence bacterial metabolic activity, extracellular polymeric substance (EPS) production, and consequently the resulting impedimetric parameters. Here, we report Bacillus cereus (B. cereus) biofilm formation on gold and indium tin oxide (ITO) surfaces in two bacterial media that promote biofilm formation. We characterized the impedance responses of biofilms formed at different time points after inoculation and demonstrated a direct correlation between variations in charge transfer resistance and biofilm structure. Non-Faradaic EIS, confocal laser scanning microscopy, and scanning electron microscopy all indicated that B. cereus exhibited faster biofilm development on ITO than on gold, possibly due to differences in surface charge or antibacterial effects associated with the nanostructured gold surface. We demonstrate a strong correlation between EIS measurements and microscopic imaging observations of early biofilm formation and the extent of biofilm development. This combination of methodologies provides a reliable approach for detecting and characterizing biofilms, particularly given the high heterogeneity and dynamic behavior of microbial communities.