Alternative Substrate Materials for Impedance Biosensors

Impedance biosensors have been widely studied for applications to biomedicine, environmental monitoring, food, and agriculture.  The most common format for AC impedance biosensors involves surface immobilization of an antibody, receptor protein, DNA strand, or other species capable of bio-recognition, and AC impedance detection of the binding event. 

One obstacle to application of impedance biosensors is the stability and reproducibility of protein immobilization.  This problem is exacerbated by the need for sensor calibration, which is typically accomplished using chaotropic reagents.  Most studies of impedance biosensors have employed amide bond formation to Au-thiol self-assembled monolayers for biomolecule immobilization.  However, this chemistry is relatively unstable, with the shelf life limited to days to weeks. 

Degenerate (highly doped) Si is an attractive alternative substrate material for impedance biosensors.  Advantages of degenerate Si include simple and reproducible surface preparation, easy incorporation into ULSI devices, and the greater strength of Si-C bonds (~520 kJ/mole) relative to Au-S bonds (125-150 kJ/mole).  Peanut protein Ara h 1 can be detected atop degenerate Si electrodes with a detection limit of < 5 ng/ml. Regeneration of antibody films atop degenerate Si using 0.2 M KSCN and 10 mM HF allows repeated detection of peanut protein Ara h 1 during a 30-day trial.  The inclusion of HF is required to periodically remove Si oxide from the substrate.  Results will also be presented for impedance biosensing with Ti/TiO₂ as the substrate material.