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F W Scheller

Publications and source records attributed to F W Scheller.

At least 19 recordsLinked to original sources
PubMed2005

Sensitive detection of organophosphates in river water by means of a piezoelectric biosensor.

A highly sensitive piezoelectric biosensor has been developed for detection of cholinesterase inhibitors. The inhibitor benzoylecgonine-1,8-diamino-3,4-dioxaoctane (BZE-DADOO) was immobilized on a monolayer of 11-mercaptomonoundecanoic acid (MUA) self-assembled on the gold surface of the sensor. The binding of high-molecular-weight cholinesterase to the immobilized cocaine derivative was monitored with a mass sensitive piezoelectric quartz crystal (quartz crystal nanobalance; QCN). In the presence of an inhibiting substance in the sample, the binding of cholinesterase to the immobilized inhibitor was reduced. The decrease of the rate of mass change was proportional to the concentration of free inhibitor in the sample. This way the affinity sensor followed anti-cholinesterase toxicity and the enzyme activity of ChE was not addressed. A assay for detection of organophosphates (OP) was optimized. Regeneration of the sensor surface was achieved with 1 mol L(-1) formic acid, which enabled 40 measurements with one sensor. All assays were carried out in a flow-through arrangement. The total measurement time (binding+regeneration) was 25 min and the detection limit for different OP (paraoxon, diisopropylfluorophosphate, chlorpyriphos, and chlorfenvinphos) was down to 10(-10) mol L(-1) (0.02 microg L(-1)). This sensor was used for determination of organophosphate (diisopropylfluorophosphate) levels in river water samples.

Biosensing Techniques↗
PubMed2004

Comparing an in vitro electrochemical measurement of superoxide scavenging activity with an in vivo assessment of antioxidant potential in Chinese tonifying herbs.

The in vitro superoxide scavenging activity (as determined by electrochemical measurement) and the in vivo antioxidant potential (as determined by a mouse model of carbon tetrachloride (CCl(4)) hepatotoxicity) of methanolic extracts prepared from 10 Chinese tonifying herbs were compared. Electrochemical measurement using a cytochrome c (Cyt. c) sensor showed that all of the tested herbal extracts exhibited a medium superoxide scavenging activity of different potency, as indicated by their IC(50) values. The in vivo measurement demonstrated that 80% of the herbal extracts displayed in vivo antioxidant potential, as assessed by the percentage of protection of the activity of plasma alanine aminotransferases and the hepatic glutathione regeneration capacity under CCl(4)-intoxicated condition. Although the in vitro antioxidant activity did not correlate quantitatively with the in vivo antioxidant potential, for 8 out of 10 samples a similar tendency was found. The rapid amperometric assessment of antioxidant potential by Cyt. c sensor may offer a convenient and direct method for screening as well as the quality control of herbal products.

Animals↗
PubMed2003

Electrochemistry of immobilized CuZnSOD and FeSOD and their interaction with superoxide radicals.

Copper, zinc superoxide dismutase (CuZnSOD) from bovine erythrocytes and iron superoxide dismutase from Escherichia coli (FeSOD) were immobilized on 3-mercaptopropionic acid (MPA)-modified gold electrodes, respectively. The characterization of the SOD electrodes showed a quasi-reversible, electrochemical redox behavior with a formal potential of 47+/-4 mV and -154+/-5 mV (vs. Ag/AgCl, 1 M KCl) for surface adsorbed CuZnSOD and FeSOD, respectively. The heterogeneous electron transfer rate constants were determined to be about 65 and 35/s, respectively. Covalent fixation of both SODs was also feasible with only slight changes in the formal potential. The interaction of superoxide radicals (O(2)(-)) with the SOD electrode was investigated. No catalytic current could be observed. However, due to the fast cyclic redox reaction of SOD with superoxide, the communication of the protein with the electrode was strongly influenced. The amperometric detection of superoxide radicals is discussed.

Adsorption↗
PubMed2002

Amperometric biosensor based on a functionalized gold electrode for the detection of antioxidants.

A method for the electrochemical detection of antioxidants has been developed, which is based on a radical measurement with a cytochrome c modified electrode. A controlled enzymatic production system for superoxide radicals based on xanthine oxidase was used. The addition of antioxidants facilitated the decomposition of the radical in addition to the spontaneous dismutation. The steady-state of superoxide generation and decomposition was thus shifted to a new situation due to the higher decomposition rate after antioxidant addition. This resulted in a decreased current level at the electrode. Antioxidant activity could be quantified from the response of the sensor electrode by the percentage of the signal decrease. The 50% inhibition value (IC(50)) for different antioxidants was calculated and the antioxidant activity of numerous substances was compared. Thus, a hierarchy of superoxide radical scavenging abilities of flavonoids was established: flavanols>flavonols>flavones>flavonones>isoflavonones.

Antioxidants↗
PubMed2001

Bioelectrochemical analysis of neuropathy target esterase activity in blood.

Bioelectrochemical analysis of neuropathy target esterase (NTE) and its inhibitors is based on the combination of the NTE-catalyzed hydrolysis of phenyl valerate and phenol detection by a tyrosinase carbon-paste electrode. The use of the tyrosinase electrode improves 10-fold the sensitivity of NTE detection in comparison with a spectrophotometric method. The tyrosinase electrode was found to be suitable for measurements in whole human blood where spectrophotometric detection is considerably restricted. The specificity of NTE in blood for mipafox and di-2-propyl phosphorofluoridate was close to that for neuronal NTE. The NTE-like activity in blood was determined to be 0.19 +/- 0.02 nmol/min/mg of protein.

Animals↗
PubMed2001

An optical method for the detection of oxidative stress using protein-RNA interaction.

The cytosolic 4Fe-4S protein aconitase can be converted under the influence of reactive oxygen species into an iron-regulatory protein (IRP1). Therefore, the IRP1 level is considered as an indirect marker of oxidative stress. An experimental approach is presented here to detect the concentration of this marker protein by surface plasmon resonance. The optical method exploits the natural binding affinity of IRP1 to an iron-responsive element (IRE) which was in vitro transcribed with a linker sequence and subsequently immobilized on a BIACORE sensor chip. The detection was found to be reproducible and sensitive in the range 20-200 nM IRP. Conditions of the binding process, such as pH and thiol concentration, were characterized. Feasibility of the method to detect and quantify IRP1 in physiological media was demonstrated.

Aconitate Hydratase↗
PubMed2001

Quinoprotein glucose dehydrogenase modified thick-film electrodes for the amperometric detection of phenolic compounds in flow injection analysis.

The use of thick-film electrodes as basic transducers for highly sensitive amperometric biosensors using PQQ (pyrroloquinoline quinone) dependent glucose dehydrogenase (GDH) with short response times is described. The enzyme is embedded in a polyurethane matrix on top of a platinum based thick film electrode and its ability to reduce oxidized phenolic compounds is exploited. The electrochemical amplification is based on the oxidation of the analyte on the surface of the electrode followed by its enzymatic reduction. Different parameters of the glucose dehydrogenase electrode system using dopamine as a model analyte were optimized, e.g., membrane thickness, pH value, buffer system, flow rate and storage conditions. Using optimized parameters the sensitivity and detection limits for various phenolic compounds were evaluated. The comparison of electrodes from the identical as well as from different batches shows the ability to produce a number of well reproducible sensors showing remarkably small differences with respect to parameters as sensitivity, response times and measuring range.

Acinetobacter calcoaceticus↗
PubMed2001

Research and development in biosensors.

Progress in biosensors has mainly been made by the improvement of the biological components and the implementation of microsystem technologies. Enzymes are still the most appropriate recognition elements because they combine high chemical specificity and inherent biocatalytic signal amplification. A breakthrough has been achieved in the application of membrane-integrated receptor systems for analyte recognition and signal transduction in biosensors. Sensor integration of RNA aptamers has been initiated, and the performance of fully synthetic molecularly imprinted polymers has been improved.

Antibodies↗
PubMed2000

Operation of a miniature redox hydrogel-based pyruvate sensor in undiluted deoxygenated calf serum.

An amperometric sensor for the detection of pyruvate in biological fluids was formed by modifying the tip of a 0.25 mm gold wire with a layer of electrically "wired" recombinant pyruvate oxidase (POP). The sensor did not require O2 for its operation. The electroactive area of the tip of the microwire was increased by electrodeposition of platinum black. The POP was adsorbed on the platinum black and then "wired" with the cross-linked, subsequently deposited poly(4-vinylpyridine), part of the pyridine functions of which were complexed with [Os(bpy)2Cl](+/2+) and part quaternized with 2-bromoethylamine. In the resulting thin layer the POP was well "wired". When the electrode was poised at 0.4 V vs Ag/ AgCl, the sensitivity at pH 6 was 0.26 A cm(-2) M(-1) and the current increased linearly with the pyruvate concentration through the 2 x 10(-6) - 6 x 10(-4) M range. Thiamine diphosphate, flavin adenine dinucleotide, and MgCl2 were not required for the assay, but stabilized the stored enzyme electrode. Placement of a dialysis membrane (MWCO 3500) on the electrode alleviated the severe interference of ascorbate. In calf serum, the detection limit was 30 microM, suggesting that the electrode might be used in the continuous monitoring of pyruvate in hypoxic organs.

Animals↗
PubMed2000

Clay-bridged electron transfer between cytochrome p450(cam) and electrode.

We demonstrate a very fast heterogeneous redox reaction of substrate-free cytochrome P450(cam) on a glassy carbon electrode modified with sodium montmorillonite. The linear relationship of the peak current in the cyclic voltammogram with the scan rate indicates a reversible one-electron transfer surface process. The electron transfer rate is in the range from 5 to 152 s(-1) with scan rates from 0.4 to 12 V/s, respectively. These values are comparable to rates reported for the natural electron transfer from putidaredoxin to P450(cam). The formal potential of adsorbed P450(cam) is -139 mV (vs NHE) and therefore positively shifted by 164 mV compared to the potential of substrate-free P450(cam) in solution. UV-VIS and FTIR spectra do not indicate an influence of the clay colloidal particles on the heme and the secondary structure of P450(cam) in solution. However, P450(cam) adsorbed on the surface of the clay-modified electrode may undergo partial dehydration resulting in the shift of the formal potential.

Bentonite↗
PubMed2000

Enzyme kinetic assays with surface plasmon resonance (BIAcore) based on competition between enzyme and creatinine antibody.

A procedure is described which allows the characterization of enzyme by a hybrid approach using an enzyme and an antibody. The presented method is related to the affinity determination of antibodies by the 'affinity in solution' procedure for BlAcore. The antibody is used as an indicator for the concentration of substrate, which is also the antigen. A mixture of enzyme, substrate and antibody is incubated, and an aliquot of this solution is injected periodically into a flowcell containing immobilized substrate, which is bound by the antibody, but not cleaved by the enzyme. The chosen initial concentration of substrate inhibits the binding of antibody to the immobilized substrate by 90%. During the enzymatic reaction, increased amounts of antibody bind to the surface, as the substrate concentration is decreased. With this method, the cleavage of creatinine with creatinine iminohydrolase (6 mU/ml) was monitored for up to 11 h. A recently developed monoclonal antibody against creatinine was used as the indicating protein. For the calculation of enzyme activity, the signals were compared with a calibration curve for inhibition of antibody binding to the chip by creatinine in solution.

Aminohydrolases↗
PubMed2000

Electrochemical investigation of cellobiose oxidation by cellobiose dehydrogenase in the presence of cytochrome c as mediator.

An important aspect of the cytochrome c electrochemistry is the possibility of coupling the 'heterogeneous reactions' with other redox enzymes. Cellobiose dehydrogenase, a 89170 Da glycoprotein that contains both FAD and a b-type haem as prosthetic groups, donates electrons to a number of acceptors, including cytochrome c. While haem b is surrounded mainly by acidic amino acids, cytochrome c displays positive charged lysine groups around the haem site. Thus a fast reaction between both proteins is explicable. In the presence of cellobiose, a catalytic current was observed, owing to the interaction of cellobiose dehydrogenase with electrostatically adsorbed cytochrome c. Adsorption of cytochrome c provides a technological model surface for vectorial electron transfer.

Carbohydrate Dehydrogenases↗
PubMed1999

Changing functionality of surfaces by directed self-assembly using oligonucleotides--the Oligo-Tag.

A method is presented to modify surfaces for biotechnological applications. Oligonucleotides have been coupled covalently to a pre-activated surface. Complementary oligonucleotides hybridize to the surface, which are conjugated with functionalities. The oligonucleotides serve as "Oligo-Tags" for these functionalities that now are linked specifically and reversibly. The approach might be used to change DNA-arrays into arrays of arbitrary ligands. We demonstrate the method with an optical wave guide grating coupler as a sensing surface using two different haptens as examples for a variety of functionalities. The haptens were 2,4-dichlorophenoxyacetic acid and atrazin and are recognized by specific antibodies. The surface created was completely regenerable by alkaline washing or temperature increase without any loss of binding capacity. Specificity was demonstrated by competitive binding of antibody in presence and absence of analyte; unspecific binding has not been observed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1998

Automated amplified flow immunoassay for cocaine.

An amplified flow immunoassay (AFIA) was developed for cocaine, which combines a noncompetitive immunoenzymometric assay (IEMA) with an on-line detection of the enzyme label alkaline phosphatase (ALP) by a substrate-recycling biosensor. In the IEMA, the analyte cocaine first binds to a labeled polyclonal anti-cocaine antibody. Then, the excess labeled antibody is separated on an affinity column that contains a perfusion chromatography carrier modified by immobilized cocaine. The unbound complexes of the analyte cocaine with the ALP-labeled antibody are detected postcolumn. The detector senses phenol produced by ALP from phenyl phosphate. As detector, an amperometric substrate-recycling biosensor was used, which consists of a Clark-type oxygen electrode covered by tyrosinase and pyrroloquinoline quinone-dependent glucose dehydrogenase. The lower limit of detection is 380 pM (38 fmol) for cocaine. The sampling rate is 26/h. Cocaine could be detected from "real samples" with an imprecision of +/- 10% (n = 3) and with a recovery of 49 +/- 3% for various concentrations. AFIA is generally important as a new approach for the fast detection of picomolar concentrations of haptens.

Alkaline Phosphatase↗
PubMed1998

A bienzyme electrode for L-malate based on a novel and general design.

The coimmobilization of a NAD(P) + -dependent dehydrogenase with salicylate hydroxylase (SHL, EC 1.14.13.1) in front of a Clark-electrode yields a flexible new design for dehydrogenase based biosensors. The feasibility of the approach has been tested with malic enzyme (MDH, EC 1.1.1.40) as the dehydrogenase, resulting in a novel L-malate sensor. It had substantial advantages over the biosensor approaches reported earlier: effective re-oxidation of NADPH by SHL yielded an extended linear range from 0.01 to 1.2 mmol 1(-1) L-malate and strongly reduced NADP+ -requirement (<0.025 mmol 1(-1)), while the working stability was increased to more than 30 days. The results obtained from six real samples showed a close correlation with the standard enzymatic method. The presented scheme with SHL and the Clark-electrode can be employed together with any NAD(P)+ -dependent dehydrogenase.

Biosensing Techniques↗
PubMed1998

Determination of L-phenylalanine based on an NADH-detecting biosensor.

An enzyme carbon paste electrode containing three different enzymes was developed for the determination of L-phenylalanine. This sensor is based on the enzymatic/electrochemical recycling of tyrosinase in combination with salicylate hydroxylase and L-phenylalanine dehydrogenase (PADH). The enzymes salicylate hydroxylase and tyrosinase were coimmobilized first in a carbon paste electrode for the sensitive detection of NADH. The principle of the bienzyme scheme is as follows: the first enzyme, salicylate hydroxylase, converts salicylate to catechol in the presence of oxygen and NADH. The second enzyme, tyrosinase, then oxidizes the catechol to o-quinone, which is electrochemically detected and reduced back to catechol at the electrode at an Eappl = -50 mV vs Ag/AgCl. This results in an amplified signal due to the recycling of the catechol and o-quinone between tyrosinase and the surface of the electrode. Prior to adding PADH, the salicylate hydroxylase-tyrosinase carbon paste electrode was characterized in terms of its sensitivity to NADH, pH dependence, buffer composition, interferences, and stability. Interference from ascorbic acid and uric acid was found to be minimal. Human serum was used to investigate whether this bienzyme system was suitable for the detection of NADH in serum and blood samples. The sensitivity for NADH was increased by a factor of 33 times using the bienzyme amplification scheme (electroreduction of o-quinone at Eappl = -50 mV) as opposed to the salicylate hydroxylase single-enzyme system (at which catechol would have been oxidized at Eappl = +150 mV vs Ag/AgCl). The detection limit for NADH achieved by the bienzyme carbon paste electrode was 1 vs 100 microM for the single-enzyme carbon paste electrode. The salicylate hydroxylase-tyrosinase system was then coupled with phenylalanine dehydrogenase for L-phenylalanine determination. This multienzyme sensor was able to achieve a linear range of 20-150 microM and a detection limit of 5 microM for L-phenylalanine. The sensitivity is sufficient since the reference clinical range for L-phenylalanine is 78-206 microM.

Amino Acid Oxidoreductases↗
PubMed1997

Catecholamine detection using enzymatic amplification.

Different amplification sensors based on the substrate recycling principle were investigated with respect to their applicability to catecholamine detection. In the bioelectrocatalytic approach, glassy carbon electrodes were modified by laccase or a PQQ-dependent glucose dehydrogenase. Substrate recycling occurs and the detection limit is in the lower nanomolar concentration range (e.g. 10 nM dopamine and 1 nM noradrenaline for the laccase- and glucose dehydrogenase-modified electrodes, respectively). Combinations of glucose dehydrogenase with laccase or tyrosinase were investigated as bienzymatic probes. Among the systems we studied, the laccase/glucose dehydrogenase sensor is the most sensitive (detection limit: 0.5 nM adrenaline). The selectivities of the different sensor systems are discussed. Application of the laccase/glucose dehydrogenase electrode in different media (i.e. brain homogenate, heart effluate) was successfully shown. For samples with high concentrations of interfering substances (uric and ascorbic acid), the interferences can be effectively removed using enzymatic methods.

Biosensing Techniques↗