Modeling and simulation of carbon nanotube-based dual-gated enzyme field effect transistor for acetylcholine detection

A model for carbon nanotube-based dual-gated enzyme field effect transistor is presented for detection of acetylcholine (ACh). Modeling is done using the enzymatic reactions of the enzyme acetylcholine esterase (AChE) on ACh substrate, diffusion phenomena of the main substrate (i.e., ACh) in phosphate buffer saline (PBS), acidic reactions of the product acetic acid (CH3COOH) in the PBS solution, the pH detection properties of ISFET and the current transport model of dual-gated CNTFET. The diffusion phenomenon of the substrate in electrolyte is modeled by Fick's law of diffusion. The use of polyethylene imine doped CNT as channel has increased the sensitivity of the device at normal temperature and pH. As the mobility of CNT is very high and a high-k dielectric HfO2 is used as top gate insulator, a small change in potential at the enzyme-insulator interface results is large current variation. The potential variation with change in pH is depicted by the model given by Bousse. This potential change varies the threshold voltage of the device, thereby varying the drain current. The simulated results of the model was compared with the characteristics of the fabricated device and found to be in good agreement.