Preparation of nanofiber-based screen-printed electrodes and biosensor applications

Biological and biochemical processes have a very important role in clinical diagnostics, medical applications, bioreactors, food quality control, agriculture, industrial wastewater control, mining and defense industries. However, converting biological data into measurable signal is a very time-consuming process. In this context, biosensors have been extensively researched, and the interest and need for biosensors that can measure with high sensitivity and selectivity is increasing rapidly. Recent studies have shown that screen-printed electrodes (SPEs), which are low-cost, suitable for miniaturization, and easy to mass-produce, represent a powerful alternative to conventional electrodes to develop new electrochemical sensing platforms and improve their performance. One of the key factors in the development of a reliable and sensitive biosensor is the preparation of a suitable matrix for the immobilization of bioreceptors. Recent studies have shown that the use of nanofiber-containing matrices has a positive effect on biosensor performance due to their large surface area. Among these matrices polyacrylonitrile (PAN) nanofibers has played a leading role due to its high tensile strength, thermal and mechanical stability, resistance to dissolution and swelling in organic solvents. In addition, it is known that the inclusion of substances called mediators, which improve the electron transfer between the active center of the enzyme and the electrode surface, contributes positively to the biosensor performance. Based on this information, in this thesis, it is aimed to produce new generation biosensors with high sensitivity by using nanofibers containing mediator, screen-printed and conventional electrodes. It is aimed to obtain PAN, PAN-MWCNT, Nylon 6-MWCNT, PAN/Methylene Blue, PAN/Neutral Red and PAN/Thionine nanofibers by cheap and simple methods and to use them as matrix in amperometric biosensors. With these electrospun matrices Glucose oxidase, Urease and Polyphenol oxidase based biosensors were prepared and all were evaluated in terms of sensitivity, linear range, stability, detection limit, interference effect and real sample analysis. In real sample analysis, commercial fruit juices were used for glucose biosensors, tap water for polyphenol biosensors and human urine samples were used for urea biosensors. Among the glucose oxidase-based biosensors, YBCE/PAN-TH-Nfs/GOx biosensor containing Thionine (TH), which was prepared without the addition of MWCNT, a conductive nanoparticle or electrochemical polymerization, was found to have the highest sensitivity with 126.73 μA/mM.cm2. In the polyphenol biosensors designed for the analysis of phenolic compounds, Pt/PAN-MWCNT-NFs/PPO biosensor revealed sensitivity of 366 μA/mM.cm2, 25 μA/mM.cm2 and 14.66 μA/mM.cm2 for catechol, p-chlorophenol and phenol, respectively. Finally, the sensitivity value obtained for the urea biosensor was determined as 325.74 μA/mM.cm2. When the biosensors prepared within the scope of the thesis study were compared with other studies in the literature, it was determined that the use of mediator and nanofiber-based matrix had a positive effect on the performance of enzyme biosensors.