Electric-Field-Assisted Enrichment and Electrochemical Detection of Gram-Positive Bacteria Using an FEM-Guided Interdigitated Electrode Biosensor

Dielectrophoretic (DEP) enrichment is a powerful strategy to enhance bacterial capture efficiency and accelerate the response of electrochemical biosensors by actively concentrating target bioparticles at the sensing interface. In this study, a combined numerical–experimental framework is developed to rationally design a DEP-assisted electrochemical biosensor with improved bacterial capture and detection performance. A finite-element modeling (FEM) approach was used to model the coupled electric field, dielectrophoretic force, and particle-transport phenomena, providing a quantitative basis for comparing bacterial trapping efficiency across different interdigitated electrode geometries. The modeling reveals that a wave-shaped interdigitated electrode (W_IDE) generates extended high-field regions and an enlarged effective capture area, resulting in an improved bacterial capture efficiency of 19% compared to 12% for the conventional rectangular interdigitated electrodes (R_IDE) under positive DEP (pDEP) conditions. Based on these insights, the W_IDE was fabricated on a printed circuit board (PCB) substrate, modified with platinum-black (Pt-black) to increase electroactive surface area, and interfaced with a custom-built 16-channel portable potentiostat unit, enabling sequential impedance measurements. The developed biosensor was applied to pDEP-assisted impedance detection of Staphylococcus aureus and Micrococcus luteus using vancomycin as the capture probe. The pDEP-assisted operation enabled rapid and highly sensitive detection down to 10 CFU/mL within 30 min with a wide linear range (10–105 CFU/mL) in 0.1× PBS, outperforming passive detection (102–105 CFU/mL) for both Staphylococcus aureus and Micrococcus luteus. In skim milk, however, the linear detection ranges shifted to 102–105 CFU/mL with pDEP-assisted detection and 103–105 CFU/mL under passive detection conditions. Overall, this work highlights the significance of combining FEM-optimized electrodes with DEP-driven enrichment to achieve improved bacterial capture, sensitivity, and robustness in electrochemical biosensors.