Immobilization of invertase on a conducting polymer of 1-(4-nitrophenyl)-2,5-di(2-thienyl)-1H-pyrrole

An immobilized invertase enzyme for the selective determination of sucrose in fruit juices

Poly(N-vinylpyrrolidone-co-butylacrylate-co-N-hydroxymethylacrylamide) has been synthesized by free radical polymerization at 70 °C. Copolymer were characterized by FT-IR, elemental analysis and viscometric methods. Invertase was immobilized onto poly(N-vinyl pyrrolidone-co-butyl acrylate-co-N-hydroxymethyl acrylamide) by entrapment method. Optimum parameters (pH, temperature, substrate concentration, amount of polymer) for immobilization to obtain maximum activity were investigated. Kinetic parameters, K_m and V_max, of the free and immobilized invertases were also assayed. Results showed that immobilization enhanced the enzyme stability against changes of pH and temperature and immobilized enzyme showed lower K_m value than free enzyme. One of the most interesting results is that the optimum operational temperature of the immobilized enzyme was 15 °C higher than that of the free enzyme. The next is the activity of the immobilized enzyme at the optimum temperature (70 °C) was approximately the same as the activity of the free enzyme at its optimum temperature (55 °C). Finally, immobilized invertase were used for determination of sucrose in commercial fruit juices. A new method and equation based on immobilized invertase were derived for determination of sucrose in commercial cheryy and pomegranate juices.

Dithienylpyrrole Electrografting on a Surface through the Electroreduction of Diazonium Salts

The control of the interface and the adhesion process are key issues for the development of new application based on electrochromic materials. In this work the functionalization of an electrode’s surface through electroreduction of diazonium generated in situ from 4-(2,5-di-thiophen-2-yl-pyrrol-1-yl)-phenylamine (SNS-An) has been proposed. The synthesis of the aniline derivative SNS-An was performed and the electrografting was investigated by cyclic voltammetry on various electrodes. Then the organic thin film was fully characterized by several techniques and XPS analysis confirms the presence of an organic film based on the chemical composition of the starting monomer and allows an estimation of its thickness confirmed by AFM scratching measurements. Depending on the number of electrodeposition cycles, the thickness varies from 2 nm to 10 nm, which corresponds to a few grafted oligomers. In addition, the grafted film showed a good electrochemical stability depending on the scan rates up to 400 V/s and the electrochemical response of the modified electrode towards several redox probes showed that the attached layer acts as a conductive switch. Therefore, the electrode behaves as a barrier to electron transfer when the standard redox potential of the probe is below the layer switching potential, whereas the layer can be considered as transparent towards the electron transfer for redox probes with a redox potential above it.

High sucrolytic activity by invertase immobilized onto magnetic diatomaceous earth nanoparticles

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Innovative biocatalyst with good properties to produce invert sugar.

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mDE-APTES-invertase showed 92.5% of residual specific activity.

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High sucrolytic activity (3358 U mg⁻¹ protein) by mDE-APTES-invertase was obtained.

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Remarkable results of thermal and storage stability, and reuse for mDE-APTES-invertase were found.

Invertase immobilized on magnetic diatomaceous earth nanoparticles (mDE-APTES-invertase) with high sucrolytic activity was obtained by an easy and low-cost method. An experimental design was carried out to investigate the best immobilization conditions and it allowed obtaining an immobilized derivative with a residual specific activity equal to 92.5%. Then, a second experimental design selected the mDE-APTES-invertase with higher specific activity in relation to other derivatives reported in the literature (2.42-fold). Thermal and storage stability for immobilized invertase were found to be 35 °C for 60 min (85% retained activity) and 120 days storage period (80% retained activity), respectively. Besides, a residual activity higher than 60% and 50% were observed for mDE-APTES-invertase after reuse in short and long term, respectively. Given the simple and efficient method to obtain an immobilized derivative with high activity, the mDE nanoparticles appear to be a promising matrix for invertase immobilization as well as for other biomolecules.

A Novel Acetylcholinesterase Biosensor: Core-Shell Magnetic Nanoparticles Incorporating a Conjugated Polymer for the Detection of Organophosphorus Pesticides

To construct a sensing interface, in the present work, a conjugated polymer and core-shell magnetic nanoparticle containing biosensor was constructed for the pesticide analysis. The monomer 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole (FBThF) and core-shell magnetic nanoparticles were designed and synthesized for fabrication of the biosensing device. The magnetic nanoparticles were first treated with silica and then modified using carboxyl groups, which enabled binding of the biomolecules covalently. For the construction of the proposed sensor a two-step procedure was performed. First, the poly(FBThF) was electrochemically generated on the electrode surface. Then, carboxyl group modified magnetic nanoparticles (f-MNPs) and acetylcholinesterase (AChE), the model enzyme, were co-immobilized on the polymer-coated surface. Thereby, a robust and novel surface, conjugated polymer bearing magnetic nanoparticles with pendant carboxyl groups, was constructed, which was characterized using Fourier transform infrared spectrometer, cyclic voltammetry, scanning electron microscopy, and contact angle measurements. This novel architecture was then applied as an immobilization platform to detect pesticides. To the best of our knowledge, a sensor design that combines both conjugated polymer and magnetic nanoparticles was attempted for the first time, and this approach resulted in improved biosensor characteristics. Hence, this approach opens a new perspective in the field of enzyme immobilization and sensing applications. Paraoxon and trichlorfon were selected as the model toxicants. To obtain best biosensor performance, optimization studies were performed. Under optimized conditions, the biosensor in concern revealed a rapid response (5 s), a low detection limit (6.66 × 10(-3) mM), and high sensitivity (45.01 μA mM(-1) cm(-2)). The KM(app) value of poly(FBThF)/f-MNPs/AChE were determined as 0.73 mM. Furthermore, there was no considerable activity loss for 10 d for poly(FBThF)/f-MNPs/AChE biofilm.

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 Parkinson's 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.

Gold nanoparticle modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine for potential use as a biosensing material

Gold nanoparticle (AuNP) modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2) was used as the biosensing platform for glucose analysis. Electrochemical measurements were carried out by following the consumed oxygen due to the enzymatic reaction of glucose oxidase (GOx) at -0.7V vs Ag/AgCl. Optimisation of pH, enzyme loading, stability experiments were carried out. Effect of NP was investigated by monitoring the signal responses at different AuNP sizes and amounts. A linear relation of y=1.597x+0.264 (R(2)=0.993) was found for glucose concentrations between 0.002 and 5.0mM. The analytical characteristics of the system were also evaluated for glucose determination in flow injection analysis (FIA) mode. Finally, the system was checked for glucose detection on real samples.