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

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 ZrO2 as gate insulator, and K/PPy/CNT composite as sensing membrane on the top of ZrO2 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 (H2O2) 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.

Modeling of carbon nanotube ISFETs with high‐κ gate dielectrics for biosensing applications

“…Because CNT‐ISFET behaves like MOSFET (Figure 8C,D), V TH(CNTFET) is also a constant (because it is analogous to V TH(MOSFET) ). V TH(CNTFET) can therefore be experimentally determined from the transfer characteristic curve of CNTFET by using extrapolation in the linear region (ELR) technique …”

“…V TH(CNTFET) can therefore be experimentally determined from the transfer characteristic curve of CNTFET by using extrapolation in the linear region (ELR) technique. 29 Because ISFET is a threshold voltage controlled device, its input is pH of the electrolyte solution. Therefore, for different pH values, V TH(CNT − ISFET) will be different.…”

“…Such models have later been extended for modeling Si‐based biologically sensitive field effect transistors (BioFETs) . As far as CNT‐based electrochemical devices are concerned, many such devices have been thoroughly investigated numerically and experimentally considering the device physics and biochemistry . To the best of our knowledge, there is no electrochemical model for CNT‐ISFET that has taken account of the site binding and current transport concepts.…”

“…26,27 As far as CNT-based electrochemical devices are concerned, many such devices have been thoroughly investigated numerically and experimentally considering the device physics and biochemistry. [28][29][30] To the best of our knowledge, there is no electrochemical model for CNT-ISFET that has taken account of the site binding and current transport concepts. Such a modeling has importance as it gives the knowledge of device physics, helps explain experimental data, and chooses the parameters for high sensitivity and selectivity of CNT-based ISFET.…”