Modelling diffusion impedance in the sensing of micron-sized particles

• Modelling of diffusion impedance in the presence of micron-sized obstructions.
• Numerical solutions based on Fick’s Law solved using finite element method.
• Numerical model was validated using polystyrene beads as model analyte.
• Proposal of data analysis approached for sensing based on diffusion impedance.
• Diffusion impedance may suffer less drifts from submicron contamination.

Development of electrochemical impedance biosensor with reliable detection output is important for bringing the technology to use in real world applications. The use of increase in charge-transfer resistance, a component of faradaic impedance, as indicator of analyte-sensor interaction is one of the conventional approaches of data interpretation. However, while charge-transfer resistance is very sensitive, it is susceptible to non-specific drifts. This study explored the use of diffusion impedance, another component of faradaic impedance, in sensing applications involving micron-sized analytes such as bacteria. Fick’s second law of diffusion and finite element method were used to simulate the effect of binding micron-sized particles on diffusion impedance. Simulations were validated with the measured impedances involving polystyrene beads as analyte model. The results showed good agreement between the simulations and experimental observations. Further analysis has led to the use of apparent diffusion number, which was derived from the diffusion impedance, as the indicator for quantifying particle binding. The experimental results showed the use of diffusion impedance had stronger correlation with electrode coverage by polystyrene beads than the conventional charge transfer resistance approach. The improved data consistency may be attributed from the different drift property of diffusion impedance.