Development of electrochemical and photoelectrochemical biosensor systems

In this thesis study, electrochemical and photoelectrochemical measurements for glucose, hydrogen peroxide, xanthine oxidase, which are biologically important were carried out. Green chemistry-based, cheap, and simple procedures were used as much as possible in the synthesis of the materials. The electrochemical biosensor was constructed from reduced graphene oxide and Au nanoparticles with the aid of tannic acid. In the photoelectrochemical biosensor systems, different semiconductors (TiO2, MoS2, g-C3N4, Co3O4, CdS: Mn, MnO2, Cu2O) and for the sensitization, Th-T dye and ruthenium complexes were used. In the experimental studies, it has been observed that with the addition of Au nanoparticles and carbon-based materials (carbon nanotubes, reduced graphene oxide) into the electrode coating material, the electrical conductivity increases and the photocurrent in photoelectrochemical systems increases. It has been determined that porous semiconductors cause more enzyme immobilization, contain more active sites, and increase photocurrent values with superior light utilization. By using slow light effect in semiconductor based inverse opal photonic crystal structures and nanotubes, superior photocurrents were obtained even in low light intensity such as luminol chemiluminescence. Finally, glucose measurement was successfully performed by using power densities obtained from a photoelectrochemical biofuel cell type biosensor system. Photoelectrochemical biosensor systems increase sensitivity by reducing undesired background noise as they use both light and electricity. Another advantage of photoelectrochemical biosensors over electrochemical biosensors is that they allow measurements at 0 potential. In this case, analyte measurements can be made with low interference effect without the need for an external power source. The most promising biosensor system has been achieved using photonic crystals. Analyte measurements were performed with satisfying accuracy even under weak chemiluminescence radiation with the slow light effect occurring in photonic crystals. In addition, since the chemiluminescence intensity obtained is proportional to the amount of analyte, the noise in the biosensor system has been reduced to the lowest possible level