Cholera Toxin Binding Studies on Aluminum Oxide Coated Surfaces for Bio-sensing Applications
Open Access
- Author:
- Poluch, Maria Linda
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Esther Winter Gomez, Thesis Supervisor
Dr. Wayne Roger Curtis, Thesis Honors Advisor - Keywords:
- Cholera Toxin
self-assembled monolayers
supported bilayers
aluminum oxide
binding coefficient
diffusion coefficient - Abstract:
- The purpose of this thesis was to study cholera toxin binding on aluminum oxide surfaces for bio-sensing applications. Cholera toxin is a multifunctional membrane protein that is known to cause cholera, an acute diarrheal infection.1 This infection, linked to over 120,000 deaths per year, is caused by infection with the bacterium Vibrio Cholerae, which secretes the cholera toxin protein.2 Cholera toxin protein binds to ganglioside GM1 found in the cell membrane of epithelial cells, where it then enters the cell. Electronic biosensors are being examined as a cost-effective biosensing method, with zinc oxide thin film transistors grabbing the greatest attention for their low deposition temperature, fabrication cost, and compatibility with intracellular material. ZnO thin film transistors are coated with aluminum oxide, which acts as the dielectric layer where the transistor stores charge. It is expected that changes in charge on this aluminum oxide surface result from the binding of cholera to a lipid membrane deposited to the aluminum oxide surface, which lead to a change in the transistor current. This will allow for the detection of cholera. The focus of this experimentation was to examine the interaction of lipid bilayers and lipid monolayers with the aluminum oxide surface, specifically the surface’s effect on the diffusion coefficient and the binding constant of cholera toxin to GM1 within the bilayers and monolayers. The binding constant will dictate the sensitivity of the ZnO thin film transistor bio-sensing device. It was found that the diffusion coefficient of lipids in bilayers on the aluminum oxide coated surface was 1.64 µm2/s and 4.71 µm2/s for lipid compositions of 99.5% DOPC, 0.5% Tx-Red and 99.0% DOPC, 0.5% Tx-Red, 0.5% GM1, respectively. For monolayers on aluminum oxide surfaces, the diffusion coefficients were found to be 1.44 µm2/s and 4.12 µm2/s for lipid compositions of 99.5% DOPC, 0.5% Tx-Red and 99.0% DOPC, 0.5% Tx-Red, 0.5% GM1, respectively. The apparent binding coefficient (dissociation constant), KD, of cholera toxin binding to GM1 in monolayers deposited on aluminum oxide surfaces was found to be 208 nM. More work is needed to confirm the findings. However, it seems promising that a ZnO thin film transistor biosensor with monolayers would be able to successfully determine the presence of cholera toxin.