A theoretical and experimental study on the detection of proteins with electrochemical impedance spectroscopy

Shanna J Smith, Purdue University

Abstract

Breast cancer is one of the deadliest diseases in existence for women in this time and age. Current methods of detection can be slow and often very painful processes. As with most types of cancer, there exists a need to discover biomarkers that would specifically detect the disease. The ability to distinguish between healthy patients and cancer patients through blood sampling would dramatically impact the future of cancer detection and diagnosis. The ultimate goal would be to integrate a type of biosensing scheme that could detect these markers in a quick and quantitative manner. The biosensor platform chosen for this research was electrochemical impedance (EIS). EIS can be used to monitor the adsorption of proteins on the surface of an electrode by following the change in impedance over time at a specific frequency. EIS has historically been applied in the study of corrosion, semiconductors, batteries, and electro-organic synthesis. Classical theory from electrochemistry can also be applied in a biological setting, where the rates of a reaction occurring on the surface of the electrode can be determined. Initial studies were conducted on a model protein system of bovine serum albumin. Here, the adsorption of bovine serum albumin (BSA) from aqueous solutions containing three specific concentrations of BSA onto three different electrode surfaces was studied. The concentrations studied were: 0.25, 0.50, and 1.00 mg/ml BSA; the surfaces studied were: unmodified gold, 16-mercaptodecanoic acid (MHA)-modified gold, and antibody immobilized on MHA-modified gold. After the initial verification studies, antigen detection in solution on a gold rotating disk electrode with immobilized antibody was performed using EIS. The antibody specifically detected the cancer-associated proliferating cell nuclear antigen (caPCNA). This antigen-antibody coupling was investigated by tracking the change in impedance over time at a specific perturbation frequency. This binding was tracked over a range of antigen concentrations in solution. The resulting curves from both sets of studies illustrated the effect of analyte concentration in solution, and the effect of surface characteristics in the system. The observed adsorption curves were described successfully using a composite model that considered both Langmuir adsorption and the multilayer/rearrangement model. Parameters for both Langmuir and the multilayer/rearrangement equations were then extracted and compared for each set of experiments. This research shows that protein interactions on the surface of a gold rotating disk electrode could be successfully monitored by tracking impedance change at a specific frequency over time.

Degree

Ph.D.

Advisors

Beaudoin, Purdue University.

Subject Area

Chemical engineering

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