Elif Erhan

An amperometric biosensor based on multiwalled carbon nanotube-poly(pyrrole)-horseradish peroxidase nanobiocomposite film for determination of phenol derivatives

An amperometric biosensor based on horseradish peroxidase (HRP) and carbon nanotube (CNT)/polypyrrole (PPy) nanobiocomposite film on a gold surface has been developed. The HRP was incorporated into the CNT/PPy nanocomposite matrix in one-step electropolymerization process without the aid of cross-linking agent. Amperometric response was measured as a function of concentration of phenol derivatives, at a fixed bias voltage of -50 mV. Optimization of the experimental parameters was performed with regard to pH and concentration of hydrogen peroxide. The linear range, sensitivity and detection limit of the biosensor were investigated for eighteen phenol derivatives. The sensitivity in the linear range increased in this order: 4-methoxyphenol>2-aminophenol>guaiacol=m-cresol>2-chlorophenol=4-chlorophenol=hydroquinone=pyrocatechol>2,6-dimethoxyphenol>3-chlorophenol>p-cresol>p-benzoquinone=4-acetamidophenol>catechol>phenol=pyrogallol=2,4-dimethylphenol. CNTs was shown to enhance the electron transfer as a mediator and capable to carry higher bioactivity owing to its intensified surface area. The biosensor exhibited low detection limits with a short response time (2s) for the tested phenolics compared to the reported working electrodes. It retained 70% of its initial activity after using for 700 measurements in 1 month.

Amperometric nitrate biosensor based on Carbon nanotube/Polypyrrole/Nitrate reductase biofilm electrode

This study describes the construction and characterization of an amperometric nitrate biosensor based on the Polypyrrole (PPy)/Carbon nanotubes (CNTs) film. Nitrate reductase (NR) was both entrapped into the growing PPy film and chemically immobilized via the carboxyl groups of CNTs to the CNT/PPy film electrode. The optimum amperometric response for nitrate was obtained in 0.1 M phosphate buffer solution (PBS), pH 7.5 including 0.1 M lithium chloride and 7 mM potassium ferricyanide with an applied potential of 0.13 V (vs. Ag/AgCl, 3 M NaCl). Sensitivity was found to be 300 nA/mM in a linear range of 0.44-1.45 mM with a regression coefficient of 0.97. The biosensor response showed a higher linear range in comparison to standard nitrate analysis methods which were tested in this study and NADH based nitrate biosensors. A minimum detectable concentration of 0.17 mM (S/N=3) with a relative standard deviation (RSD) of 5.4% (n=7) was obtained for the biosensor. Phenol and glucose inhibit the electrochemical reaction strictly at a concentration of 1 μg/L and 20 mg/L, respectively. The biosensor response retained 70% of its initial response over 10 day usage period when used everyday.

Development and operation of gold and cobalt oxide nanoparticles containing polypropylene based enzymatic fuel cell for renewable fuels.

Newly synthesized gold and cobalt oxide nanoparticle embedded Polypropylene-g-Polyethylene glycol was used for a compartment-less enzymatic fuel cell. Glucose oxidase and bilirubin oxidase were selected as anodic and cathodic enzymes, respectively. Electrode fabrication and EFC operation parameters were optimized to achieve high power output. Maximum power density of 23.5 µW cm(-2) was generated at a cell voltage of +560 mV vs Ag/AgCl, in 100mM PBS pH 7.4 with the addition of 20mM of synthetic glucose solution. 20 µg of polymer amount with 185 µg of glucose oxidase and 356 µg of bilirubin oxidase was sufficient to get maximum performance. The working electrodes could harvest glucose, produced during photosynthesis reaction of Carpobrotus Acinaciformis plant, and readily found in real domestic wastewater of Zonguldak City in Turkey.

Newly synthesized poly(glycidyl methacrylate-co-3-thienylmethylmethacrylate)-based electrode designs for phenol biosensors

A newly synthesized poly(glycidyl methacrylate-co-3-thienylmethylmethacrylate) [poly(GMA-co-MTM)] was designed to fabricate various HRP electrodes for detection of phenol derivatives. The results showed that the poly(GMA-co-MTM)/polypyrrole composite film microarchitecture provided a good electroactivity as a result of pyrrole and thiophene interaction, and provided chemical bonds for enzyme immobilization via the epoxy groups of poly(GMA-co-MTM). The glassy carbon-based working electrode displayed significantly higher performance for the same composite film configuration comparing to the gold-based working electrode. Poly(GMA-co-MTM)/polypyrrole/HRP coated glassy carbon electrode exhibited a fast response less than 3s, a high sensitivity (200 nA microM(-1)for hydroquinone), a good operational stability (%RSD values ranged between 2 and 5.1 for all phenolics), a long-term stability (retained about 80% of initial activity at the end of 40th day) and a low detection limit ranging between 0.13 and 1.87 microM for the tested.

Biological NOx removal by denitrification process in a jet-loop bioreactor: system performance and model development.

Nitrogen monoxide (NO) and nitrogen dioxide referred as NOx are one of the most important air pollutants in the atmosphere. Biological NOx removal technologies have been developing to reach a cost-effective control method for upcoming stringent NOx emission standards. The BioDeNOx system was seen as a promising biological NOx control technology which is composed of two reactors, one for absorbing of NO in an aqueous Fe(II)EDTA2− solution and the other for subsequent reduction to N2 gas in a biological reactor by the denitrification process. In this study, instead of two discrete reactors, only one jet-loop bioreactor (JLBR) was utilized as both absorption and denitrification unit and no chelate-forming chemicals were added. In other words, the advantage of better mass transfer conditions of jet bioreactor was used instead of Fe(II)EDTA2−. The process was named as Jet-BioDeNOx. The JLBR was operated for the removal of NOx from air streams containing 500–3000 ppm NOx and the results showed that the removal efficiency was between 81% and 94%. The air to liquid flow ratio (QG/QRAS) varied in the range of 0.07–0.12. Mathematical modelling of the system demonstrated that the removal efficiency strongly depends on this ratio. The high mass transfer conditions prevailed in the reactor provided a competitive advantage on removing NO gas without any requirement of chelating chemicals.

Thermostable amperometric lactate biosensor with Clostridium thermocellum l-LDH for the measurement of blood lactate

The gene for Clostridium thermocellum L-lactate dehydrogenase enzyme was cloned into pGEX-4T-2 purification vector to supply a source for a thermostable enzyme in order to produce a stable lactate biosensor working at relatively high temperatures. The purified thermostable enzyme (t-LDH) was then immobilized on a gold electrode via polymerization of polygluteraldehyde and pyrrol resulting in a conductive co-polymer. t-LDH working electrode (t-LDHE) was used for determination of lactate in CHES buffer. Amperometric response of the produced electrodes was measured as a function of lactate concentration, at a fixed bias voltage of 200 mV in a three-electrode system. The linear range and sensitivity of the biosensor was investigated at various temperatures in the range of 25-60 degrees C. The sensitivity t-LDHE increased with increasing the temperature and reached its highest value at 60 degrees C. The calculated value was nearly 70 times higher as compared to the sensitivity value of the same electrode tested at 25 degrees C. The sensing parameters of t-LDHE were compared with the electrodes produced by commercially available rabbit muscle LDH (m-LDH). The sensitivity of t-LDHE was nearly 8 times higher than that of m-LDHE. t-LDHE was found to retain its activity for a week incubation at refrigerator (+5 degrees C), while m-LDHE lost its activity in this period. t-LDHE was also tested in the presence of human blood serum. The results showed that the current increased with increasing concentrations of lactate in the human blood serum and the biosensor is more sensitive to serum lactate as well as the commercial lactate dissolved in serum as compared to the commercial lactate dissolved in CHES buffer.

A Novel Poly(Glutaraldehyde-co-Pyrrole)/Horseradish Peroxidase Composite Film Electrode

Abstract A newly synthesized copolymer, Poly(glutaraldehyde-co-pyrrole) was used to immobilize horseradish peroxidase for the construction of an amperometric biosensor for detection of phenols in a flow injection system. Infrared spectra of Poly(glutaraldehyde-co-pyrrole) showed that the incorporation of aldehyde groups into the conductive polymeric backbone was achieved. The values were found to be in the range of 0.077–0.468 mM for p-benzoquinone and 0.112–0.709 mM for catechol, at various flow rates ranging between 0.25–6 mL/min. The sensitivities at various flow rates ranged between 100–200 nA/mM for catechol and 30–100 nA/mM for p-benzoquinone. The biosensor retained its initial activity for 1 month.

Determination of mercury and nickel by amperometric biosensor prepared with thermostable lactate dehydrogenase

Abstract Response of biosensor prepared with the thermostable bacterial LDH enzyme was analyzed in the presence of mercury and nickel. For electrode preparation, the enzyme was purified and immobilized on a gold sheet coated by PGA-pyrrole polymeric material. The working electrode was tested at increasing concentration of lactate in the presence of two different concentrations of mercury and nickel. Current response of biosensor decreased from 0.32 μA to 0.09 μA and 4.13 μA to 2.63 μA when 25×10 −7 mmol/L mercury and 17×10 −5 mmol/L nickel were included in the working solution, respectively. Sensitivity of the electrode decreased from 0.010 2 μA/(mmol·L −1 ) to 0.0043 μA/(mmol·L −1 ) in the presence of 25×10 −7 mmol/L mercury. On the other hand, the presence of nickel did not result in a decrease in electrode sensitivity. The results pointed out that the prepared biosensor is useful to detect mercury in a sample containing both mercury and nickel together.

Enzyme based phenol biosensors

Phenol and its derivatives is one of the most important parameters which should be monitored in environmental engineering. They are present in many wastewater streams of the oil, paint, paper, polymer and pharmaceutical industries. Phenolic compounds reach into the food chain by wastewaters then lead to dangerous and toxic effect on aquatic organisms. Principal standard methods for quantitative phenol measurement are high performance liquid chromatography (HPLC), electrochemical capillary electrophoresis (CE), gas chromatography (GC) and colorimetric spectrophotometry. Although, these methods are analytically capable, generally they require pretreatment processes such as extraction, cleaning, dilution of the samples as well as additional chemicals. Owing to those disadvantages, researchers have focused on enzyme based amperometric biosensors for measuring phenolic compounds due to their advantages such as good selectivity, working possibility in aqueous medium, fast responding, relatively low cost of realization and storage and the potential for miniaturization and automation. Amperometric biosensors, have been developing for phenol and its derivatives, are usually prepared with working electrodes which include polyphenol oxidases (PPO) (tyrosinase and laccase) and enzyme horseradish peroxidase (HRP). HRP reaction with phenols is faster than PPO enzyme reactions, and HRP-based working electrodes show higher sensitivity in comparison to PPO-based electrodes. Thus, the usage of HRP on working electrodes can be advised for fast and effective phenol measurements. The design of a support matrix that binds the enzyme and bare electrode can be target specific providing efficient electron transport via added functional groups or nanoparticles into the composite structure of the electrode. Conducting polymers as supporting matrix are usually used as copolymers or composite films in biosensor systems since mechanical and processing properties of their homopolymers are weak (Tsai & Chui, 2007; Heras et al., 2005; Carvalho et al., 2007; Serra et al., 2001; Mailley et al., 2003). Copolymerization does not require rigorous experimental conditions, and can be employed for the polymerization of a large variety of monomers leading to the formation of new advantageous materials (Boyukbayram et al., 2006; Kuwahara et al., 2005; Yilmaz et al., 2004; Yilmaz et al., 2005). Nanomaterials have also been used to improve the operational characteristics of biosensors (Yang et al., 2006; Zhou et al., 2007; Rajesh et al, 2005; Shan et al., 2007). This improvement

Application of Bdellovibrio bacteriovorus for reducing fouling of membranes used for wastewater treatment

Abstract Background: Membrane bioreactor (MBR) systems used for wastewater treatment (WWT) processes are regarded as clean technologies. Degradation capacity of the predator bacterium, Bdellovibrio bacteriovorus, was used as a cleaning strategy for reducing membrane fouling. Method: Wastewater with different sludge age and hydraulic retention time were filtered through Poly(ether)sulphone (PES) membranes using dead end reactor. Change in filtration performance after cleaning of membrane surface by B. bacteriovorus was measured by comparison of flux values. Bacterial community of the sludge was determined by 16SrRNA sequence analysis. Community profile of membrane surface was analyzed by fluorescent in situ hybridization technique. Results: After cleaning of MP005 and UP150 membranes with predator bacteria, 4.8 L/m2·h and 2.04 L/m2·h increase in stable flux at steady state condition was obtained as compared to the control, respectively. Aeromonas, Proteus, and Alcaligenes species were found to be dominant members of the sludge. Bdellovibrio bacteriovorus lysed pure cultures of the isolated sludge bacteria successfully. FISH analysis of the membrane surface showed that Alfa-proteobacteria are the most numerous bacteria among the biofilm community on the membrane surface. Conclusion: Results suggested that cleaning of MBR membranes with B. bacteriovorus has a potential to be used as a biological cleaning method.