Preparation of a Protein- and an Aptamer-conjugated Nanomaterial and Their Application in Biosensing and Immunosensing & Electrocatalytic Activity of Carbon Electrodes Modified by Nanomaterials and Molecular Catalysts for Hydrogen Evolution Reaction

تعداد176صفحه در فایل word

Ph.D. Dissertation in Analytical Chemistry

Preparation of a Protein- and an Aptamer-conjugated Nanomaterial and Their Application in Biosensing and Immunosensing

&

Electrocatalytic Activity of Carbon Electrodes Modified by Nanomaterials and Molecular Catalysts for Hydrogen Evolution Reaction

ABSTRACT

In the first study, a sensitive and highly selective dual-aptamer-based sandwich immunosensor was reported for detection of Staphylococcus aureus (S. aureus). In this bioassay system a biotinylated primary anti-S. aureus aptamer is immobilized on streptavidin coated magnetic beads via biotin-streptavidin recognition, which serves as a capture probe. A secondary anti-S. aureus aptamer-conjugated silver nanoparticles (AgNPs ) reports the target detection. In the presence of target bacterium, an aptamer-bacterium-aptamer sandwich complex is formed on the magnetic bead surface and the electrochemical signal of AgNPs followed through anodic stripping voltammetry as the analytical signal to detect S. aureus. The proposed sandwich assay benefits from advantageous of a sandwich assay for increased specificity, magnetic beads as carriers of affinity ligands for fast magnetic separation, AgNPs for signal amplification and an electrochemical stripping voltammetry read-out for a sensitive detection. The electrochemical immunosensor has an extended dynamic range from10 to 1´10⁶ cfu/mL with a low detection limit of 1.0 cfu/mL (S/N=3). Furthermore, the possible interferences of two analog bacteria, Staphylococcus epidermidis and Escherichia coli, were studied with the detection of S. aureus. The results show that these bacteria would not interfere with the detection of target bacterium. To assess the general applicability of this sensor, the quantification of S. aureus was investigated in two water samples. The results were compared to the experimental results obtained from a plate-counting method, which demonstrated an acceptable consistency.

In the second study, direct electrochemistry of Cytochrome c (Cyt c) which was adsorbed on the surface of graphene modified electrode was investigated by cyclic voltammetry. Because of the ultrahigh electron mobility of graphene and its unique surface properties such as one-atom thickness and irreversible protein adsorption at surfaces, graphene-based materials might serve as an ideal platform for accommodating proteins and facilitating protein electron transfer. Cyt c on the surface of electrode maintains its bioactivity and shows an enzyme-like activity for the reduction of Hydrogen peroxide (H₂O₂) in the wide concentration range from 2µ M to 4mM with a detection limit of 0.4 µM, displaying a potential application for the fabrication of novel biosensors to sense H₂O₂.

In final part, electrocatalytic activity of some carbon electrodes modified by nanomaterials and molecular catalysts were studied for hydrogen evolution reaction. Hydrogen as a fuel source has received attention from researchers globally due to its potential to replace fossil-based fuels for energy production. Research is being performed on hydrogen production and utilization methods to make its use economically feasible relative to current energy sources. This part, examines electrocatalytic hydrogen production from water by electrolysis. Efforts have been made in electrocatalyst development and performance evaluation. Their performance was evaluated by various electrochemical techniques such as cyclic voltammetry, chronoamperometry and etc.