Masters Theses

Date of Award

8-2022

Degree Type

Thesis

Degree Name

Master of Science

Major

Biomedical Engineering

Major Professor

Stephen A. Sarles

Committee Members

Xiaopeng Zhao, Wei Wang

Abstract

Membrane biosensors utilize the sensitivity and control of artificial cell membranes to study cellular interactions with environmental stimuli, isolate or use transmembrane proteins for sensing, sense pathogen interactions, and screen new drugs. However, membranes alone are unable transduce electrical signals and, therefore, be used for highthroughput data collection, which limits their applications and prevents fast, large quantity testing. Bioelectronic devices on the other hand, have the ability to continuously and rapidly transduce ionic/electronic signals, but most lack the sensitivity, molecular specificity, and control that is possible with membranes via selective transport. In this thesis, artificial cell membranes are incorporated onto (organic electrochemical) transistor bioelectronic devices in order to merge electrical measurement and membrane-mediated selectivity. A droplet interface bilayer (DIB) is formed on top of a PEDOT:PSS thin film, where it introduces a stimuli-responsive barrier for ion transport to the underlying film. For example, when a sufficient voltage is applied across a bilayer containing voltage activated peptides, ion channels form in the membrane, which allow cations to flow in the direction of the electric field to the PEDOT:PSS. This flux of cations into the PEDOT:PSS de-dopes the film through hole-ion substitution, lowering the conductivity of the film and, thus, the electronic current through the PEDOT:PSS film. In comparison, prior works by other research groups assembled lipid membranes on the semiconductive channel of a transistor via vesicle fusion or solvent-assisted lipid bilayer formation. These methods yielded leaky membranes characterized by low membrane resistance. If defects exist in the membrane, ions can freely diffuse through the lipid membrane, rather than be modulated by an external stimulus and controlled by membrane ion channels. Therefore, this thesis uses those previous studies as motivation to create a more reliable method for bilayer formation on organic electrochemical transistors that yields membranes with significantly higher membrane resistance required for retaining biomolecular sensitivity and specificity.

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