چكيده به لاتين
Hemoglobin A1c (HbA1c) is a standard biomarker to measure long-term average glucose concentration for diagnosis and monitoring of diabetes. Various methods have been reported for measuring HbA1c, however, a portable and precise determination is still challenging. Herein, a new highly sensitive electrochemical nanobiosensor is developed for the specific determination of HbA1c. A nanocomposite of reduced graphene oxide (rGO) and gold with a hierarchical architecture structure was electrochemically deposited on a cheap and flexible graphite sheet (GS) electrode. The nanocomposite increased the surface area, improved the electron transfer on the electrode surface, and augmented the signal. It also provided a suitable substrate for linkage of thiolated DNA aptamer as a bioreceptor on the electrode surface by strong covalent bonding. The quantitative label-free detection was carried out by differential pulse voltammetry (DPV) in a phosphate-buffered saline (PBS) solution containing redox probe Fe(CN)6 3-/4-. The detection is based on insulating the surface in presence of HbA1c and decreasing the current, which is directly related to the HbA1c concentration. The nanobiosensor demonstrated high sensitivity of 269.2 µA. cm-2, wide linear range of 1 nM to 13.83 µM with a low detection limit of 1 nM. The biosensor was successfully used for measuring HbA1c in a blood real sample. Furthermore, it is promising to use it as a part of a point of care device for low-invasive screening and management of diabetes.
Hydrogen is considered the most important energy carrier for the future. Water electrolysis is a green method for hydrogen production and simple technology that produces very clean products. However, the main problems with this method are that this process possesses slow kinetic, consumes many energies and its common electrocatalyst is platinum (Pt) based which is an expensive and rare substance. The use of accessible electrocatalyst materials with new shapes or structures, which can reduce the overpotential for the hydrogen evolution reaction (HER) is one of the ways to increase the efficiency of the electrolyzers. In this thesis, the efficiency of two catalysts for HER is investigated. First, a GS was modified with graphene oxide (GO) and then a hyperbranched structure of gold was electrodeposited on it by controlling the electrodeposition conditions (The substrate used to build the biosensor in this thesis, which is mentioned above). The electrode surface was characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). The HER performance of the prepared electrodes was evaluated using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in a 0.5 M H2SO4 solution. The as-prepared electrode revealed outstanding HER performance with a near-zero onset overpotential (4.7 mV), overpotential of 44 mV at 10 mA. cm-2, a high current density of 127.9 mA. cm-2 at 200 mV and also satisfactory stability. Such results suggest that this electrocatalyst is promising for generating clean energy on an industrial scale.
Second (as the second catalyst for HER), cobalt disulfide (CoS2) nanostructures are synthesized using a simple hydrothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology, and electrocatalytic properties of CoS2 for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in a 0.5 M H2SO4 solution. Furthermore, chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 °C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm-2 and a small Tafel slope of 29.9 mV dec-1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS2 as a common electrocatalyst.
