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 (Q(G)/Q(RAS)) 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.

Thermodynamically designed target-specific DNA probe as an electrochemical hybridization biosensor.

Applications of molecular techniques to elucidate identity or function using biomarkers still remain highly empirical and biosensors are no exception. In the present study, target-specific oligonucleotide probes for E. coli K12 were designed thermodynamically and applied in an electrochemical DNA biosensor setup. Biosensor was prepared by immobilization of a stem-loop structured probe, modified with a thiol functional group at its 5' end and a biotin molecule at its 3' end, on a gold electrode through self-assembly. Mercaptopropionic acid (MPA) was used to optimize the surface probe density of the electrode. Hybridization between the immobilized probe and the target DNA was detected via the electrochemical response of streptavidin-horseradish peroxidase in the presence of the substrate. The amperometric response showed a linear relationship with the target DNA concentration, ranging from 10 and 400 nM, with a correlation coefficient of 0.989. High selectivity and good repeatability of the biosensor showed that the thermodynamic approach to oligonucleotide probe design can be used in development of electrochemical DNA biosensors.

Poly(glycidyl methacrylate-co-3-thienylmethylmethacrylate) as an immobilization matrix for microbial glycerol biosensing based on Gluconobacter oxydans.

A commercial strain of Gluconobacter oxydans together with a new co-polymer Poly(glycidyl methacrylate-co-3-thienylmethylmethacrylate) (Poly(GMA-co-MTM)), which provides effective immobilization in the continuous flow system, was used in the sensor design. By taking the advantages of the nano-technology, carbon nanotubes (CNTs) were also added to the cell film and the sensitivity of the sensor was increased about 15 times. During the glycerol analysis in the continuous system, it was shown that composite film was not removed from the electrode surface and film elements were not washed out from the system. Glycerol analyses were performed by using batch loaded continuously flow cell at different flow rates of 1, 2, 4, and 6mL/min. The linear range was found as 2-100mM with the detection limit (LOD) of 0.057mM according to S/N=3. The calibration graphs were obtained for Poly(GMA-co-MTM)/G. oxydans and Poly(GMA-co-MTM)/CNT/G. oxydans biofilm electrodes in FIA mode, and sensitivities were found to be 1.50nA/mM and 19.13nA/mM, respectively. In this study, Poly(GMA-co-MTM) was used for the first time as a microbial matrix and was shown to be an effective immobilization agent.

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.

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.

Amperometric phenol biosensor based on horseradish peroxidase entrapped PVF and PPy composite film coated GC electrode.

Polyvinylferrocene (PVF) was used as a mediator for the fabrication of a horseradish peroxidase (HRP)-modified electrode to detect phenol derivatives via a composite polymeric matrix of conducting polypyrrole (PPy). Through an electropolymerization process, enzyme HRP was entrapped with PPy in a three-electrode system onto a glassy carbon electrode previously covered with PVF, resulting in a composite polymeric matrix. Steady-state amperometric measurements were performed at -200 mV vs. Ag/AgCl in aqueous phosphate buffer containing NaCl 0.1 M (pH 6.8) in the presence of hydrogen peroxide. The response of the HRP-modified PVF electrode was investigated for various phenol derivatives, which were 4-chlorophenol, phenol, catechol, hydroquinone, 2-aminophenol, pyrogallol, m-cresol, and 4-methoxyphenol. Analytical parameters for the fabricated PVF electrode were obtained from the calibration curves. The highest sensitivity was obtained from the calibration of 4-chlorophenol as 29.91 nA/microM. The lowest detection limit was found to be 0.22 microM (S/N = 3) for catechol, and the highest detection limit was found to be 0.79 microM (S/N = 3) for 4-methoxyphenol among the tested derivatives. The biosensor can reach 95% of steady-state current in about 5 min. The electrode is stable for 2 months at 4 degrees Celsius.

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.

The use of microporous divinyl benzene copolymer for yeast cell immobilization and ethanol production in packed-bed reactor.

Microporous divinyl benzene copolymer (MDBP) was used for the first time as immobilization material for Saccharomyces cerevisiae ATCC 26602 cells in a bed reactor and ethanol production from glucose was studied as a model system. A very homogenous thick layer of yeast cells were seen from the scanning electron micrographs on the outer walls of biopolymer. The dried weight of the cells was found to be approximately 2 g per gram of cell supporting material. Hydrophobic nature of polymer is an important factor increasing cell adhesion on polymer pieces. The dynamic flow conditions through the biomaterial due to its microporous architecture prevented exopolysaccharide matrix formation around cells and continuous washing out of toxic metabolites and dead and degraded cells from the reactor provided less diffusional limitations and dynamic living environment to the cells. In order to see the ethanol production performance of immobilized yeast cells, a large initial concentration range of glucose between 6.7 and 300 g/l was studied at 1 ml/min in continuous packed-bed reactor. The inhibition effect of glucose with increasing initial concentration was observed at above 150 g/l, a relatively high substrate concentration. The continuous fluid flow around the microenvironment of the attached cells and mass transferring ability of cell immobilized on MDBP can help in decreasing the inhibition effect of ethanol accumulation and high substrate concentration in the vicinity of the cells.

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.

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.