Musa Kamacı

L-Dopa synthesis catalyzed by tyrosinase immobilized in poly(ethyleneoxide) conducting polymers.

1-3,4-Dihydroxy phenylalanine called as l-Dopa is a precursor of dopamine and an important neural message transmitter and it has been a preferred drug for the treatment of Parkinsons disease. In this study, with regards to the synthesis of L-Dopa two types of biosensors were designed by immobilizing tyrosinase on conducting polymers: thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinylbenzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and tyrosinase immobilized by entrapment during electropolymerization. L-Tyrosine was used as the substrate for L-Dopa synthesis. The kinetic parameters of the designed biosensors, maximum reaction rate of the enzyme (Vmax) and Michaelis Menten constant (Km) were determined. Vmax were found as 0.007 μmol/(minelectrode) for PEO-co-PPy matrix and 0.012 μmol/(minelectrode) for CP-co-PPy matrix. Km values were determined as 3.4 and 9.2 mM for PEO-co-PPy and CP-co-PPy matrices, respectively. Optimum temperature and pH, operational and shelf life stabilities of immobilized enzyme were also examined.

New Amperometric Cholesterol Biosensors Using Poly(ethyleneoxide) Conducting Polymers

Accumulation of cholesterol in human blood can cause several health problems such as heart disease, coronary artery disease, arteriosclerosis, hypertension, cerebral thrombosis, etc. Therefore, simple and fast cholesterol determination in blood is clinically important. In this study, two types of amperometric cholesterol biosensors were designed by physically entrapping cholesterol oxidase in conducting polymers; thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinyl benzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and cholesterol oxidase was immobilized by entrapment during electropolymerization. The amperometric responses of the enzyme electrodes were measured by monitoring oxidation current of H2O2 at +0.7 V in the absence of a mediator. Kinetic parameters, such as Km and Imax, operational and storage stabilities, effects of pH and temperature were determined for both entrapment supports. Km values were found as 1.47 and 5.16 mM for PEO-co-PPy and CP-co-PPy enzyme electrodes, respectively. By using these Km values, it can be observed that ChOx immobilized in PEO-co-PPy shows higher affinity towards the substrate.

Novel Photoelectrochemical Biosensors for Cholesterol Biosensing by Photonic “Wiring” of Cholesterol Oxidase

In this study, a novel approach for constructing different very sensitive and efficient photoelectrochemical biosensors called as P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ and ChOx/[Ru(bpy)3]2+, were fabricated by bonding ChOx covalently to P(SNS-NH2) modified electrode and bare thioaniline modififed gold slide, respectively, using gluteraldehyde and tethering the N-hydroxysuccinimidyl ester functionalized Ru(II)-trisbipryridine to the ChOx enzyme. In the presence of different concentrations of cholesterol, the photocurrents were obtained by irradiating of the photoelectrochemical cell containing P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ or ChOx/[Ru(bpy)3]2+ electrode as the anode under air. The bipyridine complex [Ru(bpy)3]2+ was used to activate photoinduced electron-transfer reaction and it acted as a redox mediator to activate the bioelectrocatalytic functions of ChOx. Therefore, it was shown the photonic electron-transfer wiring of ChOx with the electrode. ChOx/[Ru(bpy)3]2+ and P(SNS-NH2)/ChOx/[Ru(bpy)3)2+ biosensors showed a very good linearity between 0.05–0.9 mM and 0.00625–0.6 mM for cholesterol respective. LOD values for P(SNS-NH2)/ChOx/[Ru(bpy)3)2+ and ChOx/[Ru(bpy)3)2+ electrodes were obtained as 9.86 × 10−5 mM and 3.48 × 10−4 mM cholesterol respectively according to S/N = 3 ratios. Kinetic parameters, such as Km and Imax operational and storage stabilities, effects of pH and temperature were determined for both enzyme electrodes.