Sensör uygulamaları için polimer tabanlı cihaz yüzeylerinin fonksiyonlandırılması ve üretilmesi.

In this thesis, two types of sensors: Conjugated polymer based amperometric biosensors and a chemiresistive sensor (polymer/SWCNT) for clinical and food applications were designed, fabricated and characterized. Three chapters in this thesis focused on ethanol, glucose and cholesterol biosensors based on functional polymer/MWCNT composition, different peptide sequence containing polymer, and also copolymer of two different functional monomers, respectively. After successful electrochemical deposition of the polymers on the graphite electrode surfaces, immobilization of alcohol oxidase (AOx), glucose oxidase (GOx) and cholesterol oxidase (ChOx) were carried out. Since conjugated polymer based biosensors are recognized to be a next generation building architecture for highly sensitive and fast biosensing systems, in this thesis, it is aimed to create new biosensor systems for the quantitative detection of ethanol, glucose and cholesterol which are thought to play an important role to prevent several diseases. To construct a chemiresistive sensor, nanowires (NWs), especially carbon nanotubes (CNTs), as the basis for chemiresistor research were used. In this work, single walled carbon nanotubes (SWCNTs) due to their excellent conductivity, exceptional aspect ratios, and numerous methods available for functionalization were favored. The first step generates a surface wherein P4VP-SWCNT dispersion was spray-coated and covalently linked to the surface. The P4VP dispersant not only displays a favorable interaction with SWCNTs to stabilize debundled dispersion, but it also allows further modifications on its nucleophilic pyridyl nitrogens with alkyl halides. In the second step, a post-functionalization of P4VP-SWCNT surface via reacting with 2- bromoethanol was implemented. Finally, GOx was immobilized on the modified surface to detect glucose in beverages. As a conclusion, all devices constructed in this thesis present four new examples in biosensing applications that overcome challenges associated with analysis time, selectivity and also requirement of pretreatment of the samples. Sensor performances were also evaluated for each sensor. Additionally, surface features of the sensors and molecules were fully characterized using NMR, SEM, XPS, CV, FT-IR and Raman techniques depending on the type of sensor. To further test the sensing performance, the sensors were tested towards their specific analytes and showed promising feasibility for the quantitative analysis in beverages and human blood samples.Ph.D. - Doctoral Progra

Fabrication of a promising immobilization platform based on electrochemical synthesis of a conjugated polymer

Since conjugated polymers are an important class of materials with remarkable properties in biosensor applications, in this study, a novel glucose biosensor based on a conjugated polymer was fabricated via the electropolymerization of the monomer 10,13-bis(4-hexylthiophen-2-yl)dipyridol[3,2-a:2',3'-c]phenazine onto a graphite electrode surface. Glucose oxidase (GOx) was used as the model biological recognition element. As a result of the enzymatic reaction between GOx and glucose, the glucose amount was determined by monitoring the change in the oxygen level associated with substrate concentration via the amperometric detection technique. The proposed system possessed superior properties with K-M(app) value of 0.262 mM, 2.88 x 10(-3) mM limit of detection and 105.12 mu A mM(-1) cm(-2) sensitivity. These results show that conjugated polymer film provides an effective and stable immobilization matrix for the enzyme. Finally, the biosensor was applied successfully to several commercially available beverage samples for glucose determination proving an inexpensive and highly sensitive system applicable for real time analyses

Enzyme electrodes fabricated by dad type poly (2,5-di(furan-2-yl)thiazolo[5,4-d]thiazole) conducting polymer

Poly(2,5-di(furan-2-yl)thiazolo[5,4-d]thiazol) polymer was coated over a platinum electrode and new enzyme electrodeswere produced that are not found in the literature. The formation of polymerization was shown by cyclic voltammetry.Kinetic parameters of immobilized polyphenol oxidase enzyme were determined. Vmax and Km were obtained as 0.028 ±0.001 umol min1- electrode1- and 669.68 ± 64.73 mM respectively. The effect of reaction conditions over enzyme activitywere examined. The pH and temperature at which immobilized polyphenol oxidase enzyme showed the highest activitywere found as pH 7.5 and 45 ℃. Amount of enzyme and gluteraldehyde immobilized to the electrodes were changed and inthe examination, it was detected that it is sufficient to add 2x6 uL enzyme and 1x6 uL gluteraldehyde to the electrode. Theactivity of Pt/PTTzFr/PPO electrode was followed by 50 consequential measurements. It has been seen after 50measurements that immobilized enzyme activity is 70%. As a result of shelf life examinations, it was determined thatPt/PTTzFr/PPO electrode lost 30% of its initial activity at the end of the 50th day and the remaining activity was 70%.Calibration graph was plotted for Pt/PTTzFr/PPO electrode (y = 0.0139x + 0.0479). LOQ value was calculated as 7.827 mgmL-1 and the working interval was found as 1.0 – 90.0 mg mL1-. In total phenolic material analyses made with thiselectrode, the results found in waste water samples have also been confirmed by Folin-Ciocalteau method