Aysegul Uygun

DNA hybridization electrochemical biosensor using a functionalized polythiophene

A simple and label-free electrochemical sensor for recognition of the DNA sensor event was prepared by electrochemical polymerization of 4-hydroxyphenyl thiophene-3-carboxylate. Poly(4-hydroxyphenyl thiophene-3-carboxylate) (PHPT) was synthesized electrochemically onto glassy carbon electrode and characterized by cyclic voltammetry, FTIR and AFM measurements. An ODN-probe was physisorbed onto PHPT film and tested on hybridization with complementary ODN segments. A biological recognition can be monitored by comparison with electrochemical signal (cyclic voltammogram) of single and double strand state oligonucleotide. The oxidation current of double strand state oligonucleotide is lower than that of single strand, that is corresponding to the decrease of electroactivity of PHPT with the increase of stiffness of polymer structure. Physisorbed ODN-probe and its hybridization were observed morphologically onto ITO electrodes using AFM. The sensitivity of the electrochemical sensor is 0.02 microA/nmol, detection limit is 1.49 nmol and it has good selectivity.

RF hydrazine plasma modification of chitosan for antibacterial activity and nanofiber applications

Chitosan nano powders were modified using RF hydrazine plasma produced at low pressure (26.66Pa) with 13.56MHz frequency at a power of 100W for 30min. Characterization and investigation of the properties of plasma-modified chitosan (PMCh) and non-modified chitosan (Ch) were carried out using an optical monochromator, FTIR, florescence analysis, TGA, SEM, and X-ray techniques. FTIR spectra of PMCh indicated a band broadening at 3436cm(-1) that confirmed increasing functional groups based on H-bonding. The number of NH(2) groups was determined from fluorescence analysis. TGA analysis shows that the moisture absorption is three times higher in the PMCh structure. Ch and PMCh in PVA solutions were used to produce nanofibers by the electrospinning method; average fiber diameters were 480 and 280nm for Ch and PMCh, respectively. It was found that the antibacterial effect of PMCh is better than the Ch for Gram-positive strains.

The effect of synthesis media on the properties of substituted polyaniline/chitosan composites

Substituted polyaniline/chitosan (sPANI/Ch) composites were chemically synthesized in H(2)SO(4) and CH(3)COOH synthesis media. Structural and physical properties of the composites were characterized by using FTIR, SEM, TGA, UV-vis, XRD techniques, and conductivity measurements. The effect of synthesis media on morphology, thermal stability, conductivity, and crystalline properties was investigated. Chemical interactions between substituted polyanilines and chitosan were explained using FTIR spectra results. The different morphological surfaces were observed in SEM images of the composites. The size of the substituted polyaniline/chitosan (sPANI/Ch) composites was in nanoscale, and the composites synthesized in acetic acid media showed smaller structures than those of H(2)SO(4) media and pure chitosan. It was interpreted from XRD results that the composites have amorphous structure and the PNEANI/Ch-CH(3)COOH composite has the highest crystallinity.

Synthesis and Characterization of Some N-substituted Polypyrrole Derivatives: Towards Glucose Sensing Electrodes

Synthesis and chemical oxidative polymerization of some N-substituted pyrroles ((N-Py)s) were carried out using Clauson-Kaas method and FeCl3 in CHCl3 medium, respectively. The produced polymers, N-(p-benzoic acid)polypyrrole (NpbPPy); N-(o-aminophenyl)polypyrrole (NoaPPy); N-(m-nitrophenyl) polypyrrole (NmnPPy), were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis. An enzymatic glucose biosensor is fabricated through immobilizing glucose oxidase (GOX) into N-substitued polypyrrole matrixes. The parameters affecting the fabrication and experimental conditions of biosensors were optimized. The best biosensor results were obtained for NpbPPy matrix. The sensitivity of the proposed biosensor permitted the determination of glucose in the concentration range of 0–9.2 M with a detection limit of 1× 10− 6. The apparent Michaelis–Menten constant (KM app) for the sensor was found to be 25.95 mM.

Conducting Composites and Blends of Polythiophene and Polyoxymethylene

Abstract Conductive polyoxymethylene/polythiophene (POM/PT) composites and PT/POM blends were prepared by in situ chemical polymerization using FeCl3 oxidant and mixing in solutions, respectively. It was found that the properties of the composites and blends were different from those of homopolymers and also from each other. Formation of polymer and composites was supported by FT-IR analyses. According to the results of thermal analyses (TGA), it was shown that polymers and composites have good thermal stability. The thermal degradation temperature of POM/PT composite containing 88% PT is higher than those of the other composites. The thermal degradation temperature of PT/POM blend containing 27% POM was described as higher than that of the other blends. The morphological structures of polymers and composites were studied by scanning electron microscopy (SEM). It was found that morphological structures of composites were smoother than that of PT. The crystal structures of polymers and composites were investigated by X-ray diffraction analysis. It was found that the crystal regions increased with increasing amount of POM in the composites and blends.

Some Novel Conducting Polythiophene Derivatives: Theoretical Analysis, Synthesis, Characterization and Electroreological Properties

A series of alternating phylene and symmetrically bithiophene containing repeat units and the respective homopolymers have been synthesized and characterized by combining FTIR, UV-Vis spectroscopy, four probe conductivity measurement, TGA and SEM analysis. Quantum mechanical calculations of the structures and infrared spectra of the monomers and respective dimers were compared with experimental results. The polymers are soluble in N-methyl-pyrrolidone (NMP). The samples have conductivities of 10−5 S/cm levels. Thermal degradation analysis results indicated that poly-bithiophene derivatives have higher thermal stabilities than poly-monothiophene derivatives. All samples exhibited different surface morphologies. The electrorheological (ER) properties of polymer suspensions in silicone oil were prepared and ER behavior was investigated as a function of shear rate, electric field strength and frequency.

Comparison of Properties and Quartz Crystal Microbalance Measurements of Poly(2-ethylaniline) in the Presence of Surfactants

Poly(2-ethylaniline)(P2EANI) films were chemically deposited onto gold electrodes using ammonium persulfate as oxidant in the presence of the surfactants sodium dodecyl sulfate (SDS, anionic), tetradecyltrimethylammonium bromide(TTAB, cationic) and polyoxyethylene octyl phenyl ether(Triton-X 100, non-ionic). The doping and adsorption effects of surfactants onto the properties of P2EANI, were correlated with mass gain, and were determined in situ during polymerization of 2EANI using quartz crystal microbalance (QCM). The frequency shift of P2EANI in the presence of Triton-X 100 was very sharp and fast. TTAB exhibited the lowest frequency and mass shift among the three surfactants. P2EANIs were characterized using FTIR and UV-visible spectroscopies, TGA, conductivity measurements and SEM analysis. The latter technique showed that the polymer morphology is, as expected, affected by the incorporation of surfactants into the polymer.

Eletronical and optical characteristics of atmospheric pressure plasma enhanced chemical vapor deposition (APPECVD) system

A dielectric barrier atmospheric pressure plasma discharge system with 13,56 MHz rf power supply and matching unit is built for plasma enhanced chemical vapor and composite deposition purposes. Plasma system is optimized for maximum power transfer by homemade matching circuit and uniform glow discharge is obtained with helium and argon flow. The optical, invasive electrical probe and noninvasive electrical characteristics are examined with and without monomer flow to the system. Time resolved ICCD pictures and electrical characteristics will be given with and without of monomers introduced to the system for polymerization.

Polymerization and nano composite deposition by atmospheric pressure plasma (APPECVD)

A dielectric barrier atmospheric pressure RF plasma system has been built using 13.56 MHz RF source with an homemade matching unit. A RF glow discharge is obtained with the helium flow and furan is introduced to the system. Polyfuran deposition is obtained onto glass and the characteristics of thin film are analyzed. In the same experimental setup, polythiophene and polyfuran composites are deposited in the presence of TiO2 nano particles. The morphological, chemical structure, thermal and electrical characteristics are investigated. The plasma polymerization indicated different results than the conventional polymerization of similar thin films.