Interfacial capacitance immunosensing using interdigitated electrodes: the effect of insulation/immobilization...

Area of Science:

• Biosensor technology
• Surface chemistry
• Dielectric analysis

Background:

• Capacitive immunosensors are vital for biomolecular detection.
• Reproducibility challenges hinder their widespread application.
• Optimizing insulating and immobilization chemistries is crucial for sensor performance.

Purpose of the Study:

• To compare four different insulating/immobilization chemistries for capacitive immunosensors.
• To enhance the reproducibility and stability of sensor responses.
• To understand the relationship between surface properties and capacitive behavior.

Main Methods:

• Comparative analysis of alkyl thiol, amino silane, passive adsorption, and poly(methyl methacrylate) (PMMA) coatings.
• Equivalent circuit modeling to analyze dielectric properties and capacitive behavior.
• Atomic force microscopy (AFM) and finite element modeling (FEM) to correlate surface characteristics with electrical response.

Main Results:

• Surface binding events within interdigitated electrode gaps significantly impact capacitance changes.
• FEM confirmed a 14% higher electric field intensity in electrode gaps compared to electrode surfaces.
• PMMA conformal coating yielded the smoothest surface (Rq roughness = 0.21 ± 0.02 nm).

Conclusions:

• PMMA conformal coating provides the most reproducible and stable capacitance change (15.6 ± 0.4%) for antigen-antibody binding.
• The location of binding events (electrode gaps) is critical for sensor signal generation.
• Optimized surface chemistry is essential for reliable capacitive immunosensor performance.