Electrochemical Detection of Prostate Carcinoma Biomarkers Using Nanotechnology

The first chapter of this thesis speaks about prostate specific antigen, carbon nanotubes and horseradish peroxidase. The second chapter discusses the electrochemistry and catalysis of horseradish peroxidase (HRP) and myoglobin (Mb) covalently attached to vertically aligned carbon nanotube arrays used as a tranducer. Cyclic voltammetry results gave quasi-reversible FeIII/FeII voltammetry and electrochemical catalysis involving catalytic reduction of hydrogen peroxide for both the iron-heme enzymes in myoglobin and horseradish peroxidase coupled to the carboxylated ends of the carbon nanotube arrays by amine bioconjugation reactions. Reduction peak currents gave linear relationships with scan-rates, typical of thin layer voltammetry. Results suggest that the vertically aligned nanotube arrays behave like metal electrical conductors shuttling electrons from the external circuit to redox active sites of the enzymes. Electrode-driven peroxidase activity of myoglobin and horseradish peroxidase attached to the carbon nanotube arrays was demonstrated, with detection limits for hydrogen peroxide in buffer solutions of 100nM. Moreover, Resonance Raman characterization gave spectral signatures indicating successful fabrication of the SWNT arrays with optimum 100% coverage at FeCl3 solution at a pH of 1.7. These prototype carbon nanotube biosensors are easy to prepare, and the enzyme films were stable for weeks. The third chapter describes our initial studies in the development of our prototype immunosensor using SWNT nanotubes for electrochemical detection prostate specific antigen (PSA), a cancer biomarker protein in serum. This novel immunosensor features vertically aligned nanotubes with captured immunological complex in a sandwich format. The antigen-antibody biorecognition event was monitored using catalytic reaction involving horseradish peroxidase conjugated to a secondary antibody. This initial non-amplified approach provided a decent detection limit of 0.4ng/mL for Prostate Specific Antigen, which compare favorably with the standard enzyme-linked immunosorbent assay (ELISA). Work is in progress to lower the detection limits using specially designed bioconjuates with multiple enzyme labels for signal amplifications. These easily fabricated SWNT immunosensors show excellent promise for clinical screening of cancer biomarkers and point-of-care diagnosis. Chapter 4 is describing The Pell Scholars Honors Program Connection