Validation of the quartz tuning fork system by electrochemical method and fabrication of transferrin detecting biosensor

Quartz Tuning Forks (QTFs) are known as common oscillator components due to their stable resonant frequencies and high quality-factors. In recent years, QTFs have started to be implemented as transducers into sensor systems after the Quartz Crystal Microbalance (QCM) transducers. However, QTFs are still not widespread as biosensors in literature and there is a lack of its optimization studies. In the first step of the presented thesis study, a previously developed QTF mass-sensitive sensor system has been validated through an electrochemical method -coulometry. The system was utilized for applying calculations and finally formulizing the masschange (ng) that equals for every 1 Hz frequency shift for the standard 32768Hz QTF. In order to pursue this aim, a controlled charge migration environment is created in an electrochemical cell utilizing an electrochemical method named constant potential coulometry. This ensured a controlled mass migration onto the QTF surface. The migrated mass amount was calculated according to Faraday's Laws of Electrolysis through the migrated charge values. According to Faraday's Laws of Electrolysis, the number of electrons that passes through an electrochemical cell and the element itself effects the amount of mass that deposits on an electrode. This rule is applied for the system and a mass load value was calculated. for each calculated mass a relation was set between the frequency shift. Consequently, for each 1 Hz frequency shift that is read on the QTF sensor system, 0.48786 ± 0.21255 ng mass change occurs. In the second stage of the presented study, a qualitative biosensor system that detects transferrin, which is the most important biomarker of diseases caused by iron deficiency, has been fabricated. For any biosensor study the transducer, in this case the QTF, surface is either adsorbed with a biological receptor (non-oriented immobilization) or the receptors are immobilized by surface activation methods (oriented immobilization). QTF surfaces were treated with thiophene-3-boronic acid (T3BA) for surface activation to enable oriented anti-transferrin antibody immobilization due to the affinity between boronate and CH2 structures in the heavy chain of antibodies. The optimum surface activation treatment protocols were determined, and immobilization protocols were applied. Lastly, the response of the biosensor system after transferrin interactions were examined and the performance of the system was tested. The presented study results show that the proposed mass-sensitive QTF biosensor indicates transferrin molecules are present in 1,25 mg/mL concentration of the analyte and is low-cost and portable.