Pathogen-on-a-Chip: Impedance-Based Detection of Biofilm Formation of Staphylococcus aureus and Staphylococcus epidermidis

Bacterial biofilms are complex microbial communities that contribute to the pathogenesis of chronic infections. Therefore, it is crucial to detect biofilm-associated infections in early stages as their delayed treatment becomes more complicated. Herein, we describe a label-free electrochemical impedance spectroscopy (EIS) method for detecting biofilm formation by Staphylococcus aureus and Staphylococcus epidermidis. Printed circuit board-based biamperometric gold electrodes were modified with poly-L-lysine to enhance bacterial attachment to the sensor surface. Formation and inhibition of biofilms were evaluated based on changes in charge transfer resistance (R_ct). The control R_ct value increased by ~90 kΩ for S. epidermidis biofilm and by ~60 kΩ for S. aureus biofilms. Antibiotic-treated samples exhibited similar values to those using the control. In addition, biofilm formation was evaluated through optical microscopy using safranin staining, and the micrographs suggest significant biomass on the electrodes, whereas the control appeared clear. Atomic force microscopy was used to visualize the biofilm on the electrode surface, obtain cross-sectional profiles, and evaluate its roughness. The roughness parameters indicate that S. aureus forms a rougher biofilm than S. epidermidis, while S. epidermidis forms a more compact biofilm. These findings suggest that the optimized EIS-based method effectively monitors changes related to biofilms and serves as a promising tool for evaluation of new anti-biofilm agents, such as antibiotics, phages or antibodies.