Numerical modeling of potassium‐doped polypyrrole/carbon nanotube graphene‐based cholesterol enzyme field effect transistor

Abstract

Abstract Potassium‐doped polypyrrole/carbon nanotube (K/PPy/CNT) – based graphene enzyme field‐effect transistor has been modeled for cholesterol detection. The device consists of boron‐doped p‐type graphene as substrate, nitrogen‐doped n‐type graphene as source and drain regions, high‐κ dielectric ZrO 2 as gate insulator, and K/PPy/CNT composite as sensing membrane on the top of ZrO 2 layer. The modeling is done using the enzymatic reactions of the enzyme cholesterol oxidase on cholesterol substrate, diffusion phenomena of the main substrate (ie, cholesterol) in phosphate buffer saline, acid/base reactions of the product (H 2 O 2 ) in the phosphate buffer saline solution (pH = 7), and the pH detection properties of ion sensitive field effect transistor. The thickness of the enzyme layer here is in nanometer range, which is very less compared to other enzyme field‐effect transistors whose thickness is in micrometer range. The use of K‐doped CNT as sensing membrane has increased the sensitivity of the device at normal temperature and pH. As a result of this increased sensitivity, variations of the substrate and product concentrations are noticed even at nanometer range of the enzyme layer, which results in change in pH of the ion sensitive field effect transistor. A good fit is obtained between the modeling and experimental results.