Endokrin Bozucu Hormonlara Özgü Gravimetrik Nanosensörün Hazırlanması ve Moleküler Modellenmesi

Abstract

Natural estrogenic hormones are frequently used as birth control drugs in hormonal treatments for women and as growth precursors of farm animals in veterinary practice. These components threaten human health and wildlife when they are excreted in urine and mixed with water resources or soil, and they also cause serious side effects on aquatic organisms. Estrogenic hormones, which are widely used in postmenopausal hormone replacement therapies for women, are among the leading natural water source pollutants. Estrogenic hormones, which are included in the Endocrine Disrupting Chemical (EDC) pollutants list issued by the US Environmental Protection Agency (EPA) in 2020, can only be detected above certain limits with the detection methods used today. Equilin (Equ) is one of the estrogenic hormones with health risk level 0.35 µg/L in the chemical pollutants list. In this thesis study, a quartz crystal microbalance nanosensor was prepared for the rapid and effective real-time quantitative determination of Equ, which is one of the endocrine disrupting water pollutants, without the need for expensive devices and the use of specialists, which can measure with high precision. The interactions of both Equ and 17β-estradiol, estrone, estriol estrogenic hormones with this nanosensor system were investigated. On the other hand, interactions of these estrogenic hormones and nanosensor were investigated by computer modeling studies. The use of the AutoDock molecular modeling program has been a tool to facilitate the design of biomimetic ligands with high selectivity and affinity for the target molecule. Tyrosine (Tyr), Tryptophan (Trp) and Phenylalanine (Phe) amino acids were chosen as ligand molecules that will selectively recognize estrogenic hormones according to their three-dimensional geometric structures. By calculating the free binding energies of the intermolecular interactions of amino acids and estrogenic hormones, the molecules that interact the most with each other were determined. The molecular modeling results and the interactions between Equ and Tyr, Trp and Phe were mainly based on hydrophobic interactions. The phenyl ring, indole group and phenyl residue of Tyr, Trp and Phe molecules, respectively, were oriented to the ring structure of Equ by hydrophobic interactions. Within the scope of the thesis, estrogenic hormones were detected sensitively in a short time by affinity-based interactions in the QCM nanosensor system. The QCM nanosensor was prepared by forming a self-assembled monolayer with 11-mercaptodecanoic acid (11-MUA) and then modified with the amino acids Tyr, Trp and Phe. In this thesis, the desorption mechanism of amino acids, unlike conventional QCM sensor systems, was investigated. The detection process was based on the amount of mass removed from the surface instead of the mass increase caused by the molecules attached to the quartz crystal surface. Affinity based interactions between Equ and amino acids were investigated both theoretically by molecular modeling and experimentally by real-time QCM measurements, and the results were compared. The lowest detection limit for Equ was obtained as 4.59, 5.05 and 6.30 ng/L for Tyr, Trp and Phe modified QCM nanosensor with linear dynamic detection in the 25-500nM range, respectively. It was found that Tyr and Trp modified QCM nanosensors had higher performance compared to Phe modified one, according to the changes in resonance frequency occurring in both the detection limit and QCM sensograms. Within the scope of the thesis, Equ analysis and molecular modeling of interactions with amino acids for the first time with QCM nanosensor will shed light on many studies to be done in this field.