Design and development of new generation electrodes for use in in vitro diagnostic systems

This study aims to fabricate electrodes with properties of both gold and diamond-like carbon (DLC) thin films for in vitro diagnostic system applications for the first time. A specific self-assembly method was used to prepare conductive gold nanonetwork bonded diamond-like carbon nanofilm (CGN-DLC) electrodes with multifunctional surface and bulk properties. The nanofilms possessed a relatively high sp3 carbon fraction, a high electrical conductivity (1,4 × 103 S.cm-1) and optical band gaps of 1,42 eV and 3,87 eV. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) revealed the presence of carboxylic acid functional groups on the DLC surface. High-resolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), RAMAN spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EİS) were used to help qualitative and quantitative assessing of CGN-DLC nanofilms. TEM and SEM analyzes demonstrated the successful use of trisodium citrate and gold nanoparticles to produce CGN-DLC nanofilms. The XRD spectrum indicated the Au (111), Au (200), Au (220) and Au (311) peaks of the gold nanonetwork and the C (002), C (032) and C (111) peaks of the DLC structure. The RAMAN spectroscopy demonstrated the D and G band peaks of the diamond-like carbon structure at 1388.6 cm-1 and 1568.0 cm-1, respectively. The sp3 content of DLC film was found approximately 30 %, as well. CV and EİS demonstrated that CGN-DLC nanofilms can be used as effective electrodes in biosensor applications. In the presented thesis, a sustainable method is shown for obtaining CGN-DLC nanofilms without using harmful chemicals or physical methods. To evaluate the performance of CGN-DLC nanofilm, it was coated on a pencil graphite electrode (PGE) and used in an electrochemical biosensor for the sensitive detection of miR-NA-410-5p as a prostate cancer biomarker. No amplifica-tion and/or labeling process was used on this biosensor platform. The prepared biosensor platform was detected target miRNAs using differential pulse voltammetry (DPV) method with a linear range of 0.3 fM to 100 fM and a detection limit (LOD) of 0.27 fM. As such, the CGN-DLC nanofilm is expected to find wide application areas such as bio/sensors, photovoltaics, transistors, amplifiers, energy storage elements and biomedical.