Serife O. Hacioglu

Development of a novel biosensor based on a conducting polymer.

A new type of amperometric cholesterol biosensor was fabricated to improve the biosensor characteristics such as sensitivity and reliability. For this purpose, a novel immobilization matrix 2-(4-fluorophenyl)-4,7-di(thiophene-2-yl)-1H-benzo[d]imidazole (BIPF) was electrochemically deposited on a graphite electrode and used as a matrix for the immobilization of cholesterol oxidase (ChOx). Due to strong π-π stacking of aromatic groups in the structures of polymer backbone and enzyme molecule, one can easily achieve a sensitive and reliable biosensor without using any membrane or covalent bond formation between the enzyme molecules and polymer surface. Moreover, through pendant fluorine group of the polymer, H-bond formation between with enzyme molecules and polymer was generated. Cholesterol was used as the substrate and amperometric response was measured in correlation with cholesterol amount, at -0.7 V vs. Ag/AgCl in phosphate buffer (pH 7.0). Consequently, optimum conditions for this constructed biosensor were determined. K(M)app, I(max), LOD and sensitivity values were investigated and calculated as 4.0 nM, 2.27 µA, 0.404 µM and 1.47 mA/mM cm(2), respectively. A novel and accurate cholesterol biosensor was developed for the determination of total cholesterol in food samples.

Development of an efficient immobilization matrix based on a conducting polymer and functionalized multiwall carbon nanotubes: synthesis and its application to ethanol biosensors

Material modification is one of the hot topics recently. Hereby a novel functional monomer, 2-(4-nitrophenyl)-4,7-di(thiophen-2-yl)-1H-benzo[d]imidazole (BIPN), was synthesized for matrix generation through electrochemical polymerization. Its conducting polymer was successfully used for the biolayer construction in the biosensor preparation. The electrochemical and morphological properties were improved by the introduction of carboxylic acid functionalized multiwall carbon nanotubes (f-MWCNTs). Carboxylic acid functionalization of MWCNTs was carried out via acid treatment. The electrode surface was modified with the polymer and f-MWCNTs during electropolymerization to achieve a perfect immobilization matrix for alcohol oxidase. In order to prepare a new alcohol biosensor, alcohol oxidase (AOx) was immobilized onto the modified electrode. The modified electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy techniques. Electrochemical responses of the enzyme electrodes were monitored at -0.7 V vs. Ag reference electrode by monitoring oxygen consumption in the presence of ethanol. Kinetic parameters, operational and storage stabilities were investigated. K, Imax, LOD and sensitivity were calculated as 16.946 mM, 3.31 μA, 0.806 mM and 476 μA mM-1 cm-2, respectively. Finally, this biosensor was applied to estimate the alcohol content in various beverages successfully.

A Novel and Effective Surface Design: Conducting Polymer/β-Cyclodextrin Host–Guest System for Cholesterol Biosensor

The combination of supramolecules and conducting polymers (CPs) has gained much attention for the development of new immobilization matrices for biomolecules. Herein, an amperometric biosensor based on a novel conducting polymer, poly(2-(2-octyldodecyl)-4,7-di(selenoph-2-yl)-2H-benzo[d][1,2,3]triazole)) (PSBTz) and β-cyclodextrin (β-CD) for the detection of cholesterol, was constructed. The PSBTz film with β-CD was deposited on a graphite electrode by electropolymerization technique to achieve a suitable matrix for enzyme immobilization. Moreover, to justify the immobilization, alkyl chain containing conducting polymer (PSBTz) was designed, synthesized and electrochemically polymerized on the transducer surface. Alkyl chains in the structure of SBTz and hydroxyl groups of β-CD contributed to effective immobilization while protecting the suitable orientation of the biomolecule. Cholesterol oxidase (ChOx) was covalently immobilized onto the modified surface using N,N′-carbonyldiimidazole (CDI) as the cross-linking agent. After successful immobilization, amperometric biosensor responses were recorded at −0.7 V vs Ag/AgCl in phosphate buffer (pH 7.0). The apparent Michaelis-Menten constant (KM(app)), maximum current (Imax), limit of detection (LOD), and sensitivity values were determined: 28.9 μM, 12.1 μA, 0.005 μM, and 5.77 μA/μM cm(2), respectively. The fabricated biosensor was characterized using scanning electron microscopy (SEM) and cyclic voltammetry (CV) techniques. Finally, the prepared biosensor was successfully applied for the determination of cholesterol in blood samples.

Electrochemical Properties of Perylene Diimide (PDI) and Benzotriazole (Btz) Bearing Conjugated Polymers to Investigate the Effect of π-Bridge on Electrochemical Properties

In this study, a series of benzotriazole (BTZ) and perylene diimide (PDI) based copolymers; CoP1 and CoP2 were synthesized via Stille coupling. The effect of perylene diimide (PDI) unit on electrochemical properties of BTZ bearing polymers was investigated. In addition, two different π-bridges: thiophene and dithienopyrrole (DTP) were incorporated into polymer backbone to explore their effects on electrochemical and spectroelectrochemical properties of corresponding polymers; CoP1 and CoP2. Electrochemical and spectral results showed that while CoP1 has only n-type doping property CoP2 has an ambipolar character although p-type doping property is rare for PDI based polymers. Owing to the DTP group, CoP2 showed the lowest band gap reported up to now between perylene diimide derivatives. The effect of different π–bridges and perylene diimide (PDI) unit on the HOMO and LUMO energy levels, optical band gaps, switching time, and optical contrast were presented.

Synthesis of a benzotriazole bearing alternating copolymer for organic photovoltaic applications

A low band gap donor–acceptor (D–A) copolymer PTBTBDT, namely, poly(2-dodecyl-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole-alt-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene), was designed and synthesized via a Pd-catalyzed Stille polycondensation reaction. The polymer was characterized using 1H NMR spectroscopy, UV-vis absorption spectroscopy, cyclic voltammetry, and gel permeation chromatography (GPC). PTBTBDT has good solubility in common organic solvents, good thermal stability, broad absorption, low band gap and exhibits not only high hole mobility but also moderate photovoltaic properties. PTBTBDT displays broad absorption in the wavelength range from 300 nm to 630 nm, and its HOMO and LUMO energy levels were calculated to be −4.98 eV and −3.34 eV, respectively. Bulk heterojunction solar cells were fabricated using PTBTBDT as the electron donor and PC70BM as the acceptor. The device exhibits a power conversion efficiency of 2.12% with a current density of 5.45 mA cm−2, an open-circuit voltage of 0.72 V, and a fill factor of 54% under the illumination of AM 1.5 G, 100 mW cm−2. Under similar device fabrication conditions, the PTBTBDT based device showed considerably improved efficiency among its previously synthesized counterparts, i.e. PBDTDTBTz and PBDTBTz based devices, which have 1.7% and 1.4% efficiencies, respectively. The hole mobility of the PTBTBDT : PC70BM (1 : 2 w/w) blend reached up to 1.47 × 10−3 cm2 V−1 s−1 as calculated by the space-charge-limited current (SCLC) method. By side-chain engineering, this study demonstrates a good example of tuning the absorption range, energy level, charge transport, and photovoltaic properties of polymers.

Multipurpose selenophene containing conjugated polymers for optoelectronic applications

ABSTRACT In this study, two new conjugated polymers were synthesized including benzotriazole (BTz) as the acceptor unit and selenophene as the π bridge donor segment. These acceptors were coupled with fluorene and carbazole via Suzuki condensation reactions. Electrochemical band gaps were calculated as 2.45 eV for P1 and 2.40 eV for P2. Electrochemical and optical studies of polymers indicate that both polymers are promising candidates for organic solar cell (OSC) and polymer organic light emitting diode (PLED) applications since they have suitable HOMO-LUMO energy levels and appropriate absorption and emission band ranges. Light emitting properties of synthesized polymers were investigated and the highest luminance value was found as 6608cd/m2 for P1 at 8 V. Photovoltaic properties of polymers were investigated and the optimized device based on P2 showed 1.75% power conversion efficiency for P2 under AM 1.5 G illumination at 100 mW/cm2.

Selenophene as a Bridge in Molecular Architecture of Benzotriazole Containing Conjugated Copolymers to Gain Insight on Optical and Electrochemical Properties of Polymers

GRAPHICAL ABSTRACT Abstract Polymers containing selenophene as a π bridge; poly(2-(2-octyldodecyl)-4-(selenophen-2-yl)-7-(5-(thiophen-2-yl)selenophen-2-yl)-2H-benzo[d][1,2,3]triazole) (P1) and poly(2-(2-octyldodecyl)-4-(5-phenylselenophen-2-yl)-7-(selenophen-2-yl)-2H-benzo[d][1,2,3]triazole (P2) were synthesized via Stille and Suzuki coupling reactions, respectively. Optical and electrochemical properties were investigated and comparisons with their thiophene analogs were done. Selenophene substitution resulted in low band gap and red shifted absorption, fast switching times (less than 1 s) with reasonable optical contrast. Switching time of P2 was 0.2 second which is the fastest switching time regarding benzotriazole-based polymers. Photovoltaic properties of P1 and P2 were investigated. The optimized devices showed 0.45% and 0.75% power conversion efficiency, respectively.

Syntheses and Optical Properties of Perfluorophenyl Containing Benzimidazole Derivatives: The Effect of Donor Units

Synthesis of two novel donor – acceptor – donor type monomers containing benzimidazole as the acceptor unit and thiophene and 3,4-ethylenedioxythiophene (EDOT) as the donor units were performed. 2-(Perfluorophenyl)-4,7-di(thiophen-2-yl)-1H-benzo[d]imidazole and 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-(perfluorophenyl)-1H-benzo[d]imidazole were synthesized successfully and polymerized electrochemically. The electrochemical and spectroelectrochemical studies of the polymers were studied. The effect of electron donating moieties on the optical properties of electrochemically polymerized polymers was investigated. Both polymers were p type dopable and possessed multi-chromic property. Optical studies demonstrated that the polymer based on EDOT unit (P2) resulted in lower band gap since EDOT is higher electron donating group than thiophene.

Structure–property relations in donor–acceptor–donor type benzimidazole containing conjugated polymers

In order to gain deeper insight about structure–property relations properties, two novel donor–acceptor–donor type monomers were studied. 4′-Tert-butyl-4,7-di(thiophen-2-yl)spiro[benzo[d]imidazole-2,1′-cyclohexane] and 4,7-di(2,2′-bithiophen-5-yl)-4′-tert-butylspiro[benzo[d]imidazole-2,1′-cyclohexane] were synthesized and electrochemically polymerized. Electrochemical and optical properties of the polymers were investigated via cyclic voltammetry and UV–Vis–NIR spectroscopy techniques. It was found that changing donor unit from thiophene to bithiophene results in a drastic change in optical and electrochemical properties, especially in optical contrast.Graphical AbstractIn this study, we investigate the effect of conjugation on the properties of electrochemically synthesized polymers. For this purpose, 4,7-dibromo-4′-(tert-butyl)spiro[benzo[d]imidazole-2′-cyclohexane] was synthesized as an acceptor unit and coupled with two different donor units, namely thiophene and bitihophene. Their optical and electronic properties were compared and spectroelectrochemical studies showed that with increasing conjugation, absorption maxima is red shifted together with a decrease in the optical band gap.

Syntheses, electrochemical and spectroelectrochemical characterization of benzothiadiazole and benzoselenadiazole based random copolymers

ABSTRACT Three novel donor-acceptor-donor type random copolymers based on benzothiadiazole (BTh) and benzoselenadiazole (BSe) were synthesized via Pd (0) catalyzed Suzuki polycondensation reaction. The two acceptor units were coupled with electron rich moieties which are carbazole (CZ), fluorene (FL) and silafluorene (SiFL). Monomers were characterized using 1H and 13C-NMR spectroscopy. The number and weight average molecular weights of the polymers were calculated using gel permeation chromatography (GPC). All three polymers were electrochemically and spectroelectrochemically characterized. PBThBSeCZ, PBThBSeFL and PBThBSeSiFL showed only p-dopable character and their doping/dedoping potentials were determined as 1.4 V/1.2 V, 1.53 V/1.27 V and 1.8 V/1.3 V, respectively. Corresponding HOMO energy levels were calculated as −5.85 eV, −6.05 eV and −6.15 eV whereas LUMO energy levels were found to be −3.67 eV, −3.84 eV and −3.77 eV, respectively. PBThBSeCZ had lower HOMO level and band gap than PBThBSeFL and PBThBSeSiFL due to its increased electron donating capability of nitrogen atom in carbazole unit.