Elektrokimyasal İmpedimetrik Sensörlerin Geliştirilmesi ve Uygulamaları
Yaman, Yeşim Tuğçe
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Electrochemical impedance spectroscopy (EIS) is a powerful non-destructive method to investigate the boundaries between materials with different conductivity types. With the technological development, the application areas of EIS have expanded considerably. Among these, its use in sensor studies is very important because it has advantages over other electrochemical techniques. Therefore, impedimetric sensors usage has increased dramatically in recent years due to its superior features. Hence, EIS appears as a low cost and potential approach in the quantitative determination of important analytes. EIS is a very attractive technique for biosensor development as it is a non-destructive method that provides high quality data by directly converting biological phenomena into electrical signals. Within the scope of the thesis, fast, a high sensitive and low technology impedimetric sensors without the need for complex devices for quantitative analysis of three different analytes was prepared and their application was investigated. The use of nanomaterials in impedance sensors provides advantages such as increased sensor surface area, electrical conductivity, chemical accessibility and electrocatalysis. Electrode surfaces developed for 3 analytes were modified with various nanomaterials and composites. Human serum albumin-montmorillonite (Mt-HSA) nanocomposite was used as an electrode modification agent, which had remarkable features such as good biocompatibility, large surface area and creating a suitable environment for cell immobilization for the impedimetric analysis of MCF-7 cells, which is a CTC type. The nanocomposite synthesized with desolvation method was structurally clarified by various characterization methods. The linear range was found as from 1.5 × 102 to 7.5 × 106 MCF-7 cells/mL and LOD was found to be 148 cells mL-1. From these results, a simple, label free, cost effective and rapid method for the diagnosis of breast cancer was developed by examining the interaction of Mt-HSA NCs/PGE surface with MCF-7 cells. In the second part, peptide nanotube-gold nanoparticle (PNT-AuNP) modified disposable sensors providing high electro-catalytic effect, high nucleic acid-affinity and good biomimetic activity were developed for quantitative analysis of microRNA 410. Low LOD value was established as 3.90 fM with a wide linear range from 10 fM to 300 pM for the impedimetric recognition of miRNA 410 based on hybridization process. High sensitivity and LOD were successfully attained without using any labelling or signal amplification molecules. Besides, peripheral serum sample was chosen as a complex bio-matrix environment and recovery studies were performed, which provided acceptable recovery % values. The proposed sensor platform offered high selectivity-stability, fast response time and low cost for the ultra-trace level determination of microRNA 410 in a good dynamic range and appeared as compatible with most of the conventional reported miRNA sensors. Finally, molecularly imprinted over-oxidized polypyrrole-graphene oxide (MIP (oPPy)–GO) modified disposable sensors were developed for the impedimetric detection of 3-MCPD for the first time. All developed sensor surface modifications were characterized by various methods. To evaluate the most appropriate sensor response, various experimental conditions (such as polymeric film thickness, analyte/monomer ratio, desorption/adsorption time etc.) were discussed and optimized. The electrochemistry of a redox probe (ferrocyanide/ferricyanide) was utilized for the impedimetric detection of 3-MCPD with a dynamic linear range of 2-500 nM and low LOD as 1.82 nM. In order to demonstrate the practical applicability, standard addition method was utilized in soy sauce samples. The combination of GO and oPPy in such an MIP platform provided a superior recognition performance for 3-MCPD in a label-free, disposable and cost-effective way.