Development of Raman and Electrochemical Biosensors and Fabrication of Hybrid Materials for Supercapacitors

Abstract

This dissertation describes the development of sensors for the detection of biologically relevant molecules and the fabrication of hybrid supercapacitor materials for energy storage purposes. Specifically, DNA sensors based on surface-enhanced Raman spectroscopy (SERS) and electrochemical proximity assay (ECPA) are described. Both sensors have great potential for point-of-care testing and research has focused recently on point-of-care analysis with the goal of speeding up the disease diagnosis. It is also convenient for use in poor or remote areas where highly trained personnel are not readily available. Hybrid supercapacitors, on the other hand, exhibit high power and energy densities and can undergo several charging/discharging cycles without significant loss in performance. Mn3O4 has emerged recently as a potential candidate due to the fact that Mn is earth-abundant and therefore inexpensive. The oxide can be easily deposited electrochemically on substrates such as stainless steel and carbon fibers to form hybrid materials that exhibit higher performances than the oxide alone. Chapter 1 gives a brief introduction of the principles of surface-enhanced Raman spectroscopy and the fabrication techniques of surface-enhanced Raman spectroscopy substrates. Also, recent biosensor developments based on surface-enhanced Raman spectroscopy and electrochemistry techniques are described. In addition, the principles of supercapacitors are described and their preparation is briefly reviewed.Chapter 2 describes the preparation of SERS-active substrates and their biosensor applications. Ag/Au film over nanosphere substrates (FONs) have been prepared, and a large enhancement of Raman intensity was achieved. In addition, the distance dependence of the Raman signal from the nanostructure responsible for signal enhancement is reported. Chapter 3 describes a DNA biosensor system, developed for detection of DNA sequences using Ag/Au FONs substrate. By incorporating the sensor system into a microfluidic channel, the reproducibility of the system was significantly improved. Chapter 4 presents two kinds of hybrid materials, namely carbon fiber and stainless steel fiber with Mn3O4 for supercapacitor application. These materials were found to exhibit very high capacitance. Chapter 5 deals with the optimization of the ECPA biosensor system. By incorporating uracil bases into DNA sequences, a reusable sensor was successfully developed with good signal recovery and selectivity. A faster detection (3 minutes) was also achieved, and the detection of insulin concentration in blood serum was demonstrated. Finally, Chapter 6 summarizes the research work and presents possible future directions that would follow this work.