Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Electrical Engineering

First Advisor's Name

Shekhar Bhansali

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Ajeet Kaushik

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Benjamin Boesl

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Bruce McCord

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Nezih Pala

Fifth Advisor's Committee Title

Committee Member

Sixth Advisor's Name

Ou Bai

Sixth Advisor's Committee Title

Committee Member

Keywords

Thin Film, Immunosensors, Molecularly Imprinted Polymer, Thermally Stable biosensors, Electrical Sensing, Electrochemical Biosensing, EGFET

Date of Defense

11-5-2018

Abstract

This dissertation explores the different ways to create thin film-based biosensors that are capable of rapid and label-free detection of cortisol, a non-specific biomarker closely linked to stress, within the physiological range of 10pM to 10 uM. Increased cortisol levels have been linked to stress-related diseases, such as chronic fatigue syndrome, irritable bowel syndrome, and post-traumatic stress disorder. It also plays a role in the suppression of the immune system as well. Therefore, accurate measurement of cortisol in saliva, serum, plasma, urine, sweat, and hair, is clinically significance to predict physical and mental diseases.

In this dissertation, thin film-based electrochemical immunosensors were fabricated using a self-assembled monolayer (SAM) functionalized by cortisol specific antibodies to detect cortisol at 10 pM level sensitivities in the presence of a redox probe. The fabricated electrochemical cortisol immunosensors were able to detect cortisol in human saliva samples and the outcomes were validated using the standard Enzyme Linked Immuno Sorbent Assay (ELISA) technique. With the aim of improving signal amplification and label-free cortisol detection, copper nanoparticles were incorporated on screen-printed carbon electrodes (SPCE) for the fabrication of electrochemical cortisol immunosensor. This SPCE-based sensor showed a sensitivity of 4.21µA/M and the limit of detection 6.6nM.

Both the SAM and SPCE-based immunosensors were not thermally stable due to the instability of antibodies at room temperature. To address this issue, an antibody-free immunosensor was fabricated. Molecular Imprinted Polymer (MIP) was used to template the target cortisol molecule. The MIP-based sensing platform was prepared using polypyrrole, a thermally stable conducting polymer. The conductivity of the polymer ensured good electrical performance. The polypyrrole-based MIP was synthesized by means of electrochemical polymerization and was used to detect cortisol within the physiological range at room temperature. MIP-based sensors exhibited the detection limit of 1 pM, and were cost-effective, easy to fabricate, temperature stable, and reusable. The sensing performance of the resulting sensors was comparable to those of commercially available technologies, such as ELISA. Aiming to perform cortisol sensing at point-of-care (POC), an Extended Gate Field Effect Transistor (EGFET) was integrated with a developed MIP cortisol sensor. The as developed MIP-EGFET sensor was used to detect the cortisol concentration in the range of 1 pM to 100 nM. A few of the major advantages of the developed sensor are its ability to provide a direct readout and simpler electronic systems, which are necessary for miniaturized Point of Care devices.

Identifier

FIDC007015

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Available for download on Monday, October 19, 2020

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