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Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor./
Author:	Gupta, Akanksha.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	183 p.
Notes:	Source: Dissertations Abstracts International, Volume: 83-06, Section: B.
Contained By:	Dissertations Abstracts International83-06B.
Subject:	Biomedical engineering. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28929310
ISBN:	9798494497468

Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor.
Gupta, Akanksha.

Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 183 p.

Source: Dissertations Abstracts International, Volume: 83-06, Section: B.

Thesis (Ph.D.)--The Pennsylvania State University, 2021.

Zinc oxide thin film transistors (TFTs) and lipid membranes have been investigated in this work for electronic biosensing applications. The principle of working of this electronic biosensor is based on the change of surface charge distribution after biofunctionalization of ZnO TFTs with lipid membranes. For fabricating lipid membrane based electronic biosensor, lipid monolayers provide a more stable and less charge-shielded environment than lipid bilayers and can improve the sensitivity of the biosensor. It was also found that a double gated ZnO TFT (bottom metal gate and top gate for the electrolyte) provided better control for electronic biosensing application than the commonly used electrolyte-gated transistor devices. This thesis addresses several elements and challenges encountered on the way of integrating lipid membranes with ZnO TFTs to make a stable and robust electronic biosensing platform. This thesis also emphasizes on the importance and advantages of using a gated ZnO TFT for electronic biosensing applications.The first element was to be able to coat ZnO TFTs with lipid membranes and electrically measure the devices without interfering with the lipid assemblies. For this purpose, long leads of ZnO TFTs were integrated with polymethylglutarimide (PMGI) microfluidics to deliver biofluids precisely to the active area of the ZnO TFTs while the electrical measurements can be performed on the long leads. PMGI channels can be conveniently fabricated with micrometer and sub-micrometer thickness and lateral dimensions and do not require additional processing to provide leakage-free edges, unlike some other commonly used microfluidic materials. An approach to exchange fluids to and from thin PMGI microfluidic channels using hydrated hydrogel has also been discussed.The second piece was to get stable ZnO TFTs that were not attacked during biofunctionalization on their surfaces. A stable lithography process to lift-off source and drain was found to be crucial to get stable devices. PMGI was used as a material to develop a tri-layer lithography process to fabricate source and drain contacts of ZnO TFT. The commonly used bi-layer lithography process consisting of polymethylmethacrylate (PMMA) and Novolac resist has been known to have a non-uniform intermixed layer. The process of using PMGI as the barrier between PMMA and Novolac was investigated, and a stable lift-off process was developed. The intermixed layer between PMMA and PMGI was found to be ~ 20 nm thick and more uniform than the one between PMMA and Novolac.Several challenges during the integration of lipid monolayers with ZnO TFTs were encountered. One such example was etching of aluminum oxide (Al2O3) passivation layer of ZnO TFTs after functionalizing with DI water resulting in large leakage gate currents and impractical devices. Though Al2O3 is stable in pH 4-8.5 range, it was found that the local pH generated at the interface of Al2O3 and DI water was beyond 4-8.5 while performing electrical measurements on ZnO TFTs with water. A voltage range (-1V to 0.25V) was established in which Al2O3 was stable using TCAD Sentaurus simulations. This stability window can be modified by the addition of salts.Electrical measurements were performed with neutral and negatively charged phospholipid monolayers functionalized on ZnO TFTs. It was demonstrated that the difference between the gate voltage for negatively charged lipid with respect to neutral lipid was ~ 0.1V. These electrical measurements have been supported by TCAD Sentaurus simulations and are in close agreement with each other. Although, this is a much smaller difference for what has been demonstrated for electronic biosensors in literature, TCAD Sentaurus simulations clearly indicated the sensitivity of electronic biosensor in a bio-environment with charge screening and ion shielding effects. Even though the stability and device characteristics of the ZnO TFTs could be improved, the ZnO TFT-lipid monolayer electronic biosensor platform developed in this thesis provides valuable elements for developing a more stable and robust electronic biosensor to detect other biomolecules and assemblies.

ISBN: 9798494497468Subjects--Topical Terms:

535387
Biomedical engineering.
Subjects--Index Terms:

Zinc oxide thin film transistors

Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor.
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245 1 0 $a Zinc Oxide Thin Film Transistor (Zno TFT) - Lipid Membrane Based Electronic Biosensor.
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520 $a Zinc oxide thin film transistors (TFTs) and lipid membranes have been investigated in this work for electronic biosensing applications. The principle of working of this electronic biosensor is based on the change of surface charge distribution after biofunctionalization of ZnO TFTs with lipid membranes. For fabricating lipid membrane based electronic biosensor, lipid monolayers provide a more stable and less charge-shielded environment than lipid bilayers and can improve the sensitivity of the biosensor. It was also found that a double gated ZnO TFT (bottom metal gate and top gate for the electrolyte) provided better control for electronic biosensing application than the commonly used electrolyte-gated transistor devices. This thesis addresses several elements and challenges encountered on the way of integrating lipid membranes with ZnO TFTs to make a stable and robust electronic biosensing platform. This thesis also emphasizes on the importance and advantages of using a gated ZnO TFT for electronic biosensing applications.The first element was to be able to coat ZnO TFTs with lipid membranes and electrically measure the devices without interfering with the lipid assemblies. For this purpose, long leads of ZnO TFTs were integrated with polymethylglutarimide (PMGI) microfluidics to deliver biofluids precisely to the active area of the ZnO TFTs while the electrical measurements can be performed on the long leads. PMGI channels can be conveniently fabricated with micrometer and sub-micrometer thickness and lateral dimensions and do not require additional processing to provide leakage-free edges, unlike some other commonly used microfluidic materials. An approach to exchange fluids to and from thin PMGI microfluidic channels using hydrated hydrogel has also been discussed.The second piece was to get stable ZnO TFTs that were not attacked during biofunctionalization on their surfaces. A stable lithography process to lift-off source and drain was found to be crucial to get stable devices. PMGI was used as a material to develop a tri-layer lithography process to fabricate source and drain contacts of ZnO TFT. The commonly used bi-layer lithography process consisting of polymethylmethacrylate (PMMA) and Novolac resist has been known to have a non-uniform intermixed layer. The process of using PMGI as the barrier between PMMA and Novolac was investigated, and a stable lift-off process was developed. The intermixed layer between PMMA and PMGI was found to be ~ 20 nm thick and more uniform than the one between PMMA and Novolac.Several challenges during the integration of lipid monolayers with ZnO TFTs were encountered. One such example was etching of aluminum oxide (Al2O3) passivation layer of ZnO TFTs after functionalizing with DI water resulting in large leakage gate currents and impractical devices. Though Al2O3 is stable in pH 4-8.5 range, it was found that the local pH generated at the interface of Al2O3 and DI water was beyond 4-8.5 while performing electrical measurements on ZnO TFTs with water. A voltage range (-1V to 0.25V) was established in which Al2O3 was stable using TCAD Sentaurus simulations. This stability window can be modified by the addition of salts.Electrical measurements were performed with neutral and negatively charged phospholipid monolayers functionalized on ZnO TFTs. It was demonstrated that the difference between the gate voltage for negatively charged lipid with respect to neutral lipid was ~ 0.1V. These electrical measurements have been supported by TCAD Sentaurus simulations and are in close agreement with each other. Although, this is a much smaller difference for what has been demonstrated for electronic biosensors in literature, TCAD Sentaurus simulations clearly indicated the sensitivity of electronic biosensor in a bio-environment with charge screening and ion shielding effects. Even though the stability and device characteristics of the ZnO TFTs could be improved, the ZnO TFT-lipid monolayer electronic biosensor platform developed in this thesis provides valuable elements for developing a more stable and robust electronic biosensor to detect other biomolecules and assemblies.
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653 $a Lipid membranes
653 $a Electronic biosensing applications
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773 0 $t Dissertations Abstracts International $g 83-06B.
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