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At least 1,153 records · Page 64Linked to original sources

PubMed2003

HRP-based biosensor for monitoring rifampicin.

Pyrrole was electropolymerized onto a Pt electrode in the presence of LiClO(4) and horseradish peroxidase (HRP). This HRP-based biosensor has been used for the amperometric detection of rifampicin (RIF) in the presence of a constant concentration of H(2)O(2). The C(H(2)O(2)) as well as the applied potential (E(ap)) and the pH of the phosphate buffer have simultaneously been optimized through a central composite design. Under these conditions, repeatability, reproducibility, and stability of the modified electrode have been analyzed. The detection limit for RIF has been calculated taking into account the probability of false-positive (alpha) and -negative (beta), reaching a value of 5.06x10(-6) mol dm(-3). The biosensor was applied to the determination of RIF in pharmaceutical preparations and biological samples.

Biosensing Techniques↗

PubMed2003

Flow-injection-type biosensor system for salivary amylase activity.

The authors aim to establish a method that can quantitatively evaluate vital reactions to stress. We have been examining the correlation between stress and salivary amylase activity in order to verify its validity as a stress index. In order to quantify human stress, which changes over time, the relationship between stress and salivary amylase activity must be verified by fast and repeated analysis of salivary amylase activity. Standard biosensors are designed such that the enzyme immobilized on an electrode (enzyme electrode) and the substrate-dependent activity is measured. The reverse approach of measuring the alpha-amylase-dependent activity was adopted. We fabricated an amylase activity analytical system. Maltopentaose was selected as a substrate for alpha-amylase and a flow-injection-type device was used to supply maltopentaose continuously. alpha-Glucosidase, having relatively low enzyme activity, was immobilized on a pre-activated membrane so that it could be enclosed in a pre-column, Glucose oxidase, having higher enzyme activity, was immobilized on a working electrode so that it could function as an amperometric biosensor. A saliva-collecting device was fabricated to make saliva pretreatment unnecessary. As a result, an amylase activity analytical system was fabricated that enabled us to measure salivary amylase activity from 0 to 30 kU/l, with an R(2) value of 0.97. The time-course changes in the salivary amylase activities for 1 week were 5.1%, and the initial sensitivity remained nearly constant. Through this study, we were able to verify the possible development of the amylase activity analytical system.

Amylases↗

PubMed2003

Bienzyme biosensors for glucose, ethanol and putrescine built on oxidase and sweet potato peroxidase.

Amperometric biosensors for glucose, ethanol, and biogenic amines (putrescine) were constructed using oxidase/peroxidase bienzyme systems. The H(2)O(2) produced by the oxidase in reaction with its substrate is converted into a measurable signal via a novel peroxidase purified from sweet potato peels. All developed biosensors are based on redox hydrogels formed of oxidases (glucose oxidase, alcohol oxidase, or amine oxidase) and the newly purified sweet potato peroxidase (SPP) cross-linked to a redox polymer. The developed electrodes were characterized (sensitivity, stability, and performances in organic medium) and compared with similarly built ones using the 'classical' horseradish peroxidase (HRP). The SPP-based electrodes displayed higher sensitivity and better detection limit for putrescine than those using HRP and were also shown to retain their activity in organic phase much better than the HPR based ones. The importance of attractive or repulsive electrostatic interactions between the peroxidases and oxidases (determined by their isoelectric points) were found to play an important role in the sensitivity of the obtained sensors.

Alcohol Oxidoreductases↗

PubMed2003

Microdevice with integrated dialysis probe and biosensor array for continuous multi-analyte monitoring.

The simultaneous on-line determination of glucose and lactate using a microdevice that consisted of a dialysis sampling system incorporated to the flow-through cell of a microfabricated biosensor array is presented. The fluidic connections between the different device's components were realized by subsequent processing of stacked dry resist layers on a plastic support that provided also the means for electric connections. The performance of the device was evaluated in vitro. The cross-talk effect on the downstream sensor was investigated and found to be negligible. Recoveries of over 95% for both analytes were achieved when flow rates of the perfusion fluid </=0.5 microl/min were used. At this flow rate, the response time of the device was 2.4 min, which is acceptable for on-line analysis. The linear response concentration range extended up to 30 mM for glucose and 15 mM for lactate. Interference from electroactive species such as ascorbic acid, 2-acetamidophenol and uric acid, was minimal (less than 5% increase in biosensors signal for all substances tested). In addition, the device presented long-term run stability both in buffer and serum samples.

Artifacts↗

PubMed2003

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva.

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol-gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be rho=-0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.

Biosensing Techniques↗

PubMed2003

A disposable microbial based biosensor for quality control in milk.

The food industry needs suitable analytical methods for quality control, that is, methods that are rapid, reliable, specific and cost-effective as current wet chemistries and analytical practices are time consuming and may require highly skilled labor and expensive equipment. The need arises from heightened consumer concern about food composition and safety. The present study was carried out keeping in view the recently emerging concern of the presence of urea in milk, called "synthetic milk". The biocomponent part of the urea biosensor is an immobilized urease yielding bacterial cell biomass isolated from soil and is coupled to the ammonium ion selective electrode of a potentiometric transducer. The membrane potential of all types of potentiometric cell based probes is related to the activity of electrochemically detected product, and thus to the activity of the substrate by a form of the Nernst equation. Samples of milk were collected and analyzed for the presence of urea by the developed biosensor with a response time as low as 2 min. The results were in good correlation with the pure enzyme system.

Animals↗

PubMed2003

New principle of direct real-time monitoring of the interaction of cholinesterase and its inhibitors by piezolectric biosensor.

This paper describes a new method for the sensitive detection of cholinesterase inhibitors based on real-time monitoring using a piezoelectric biosensor. The cholinesterase inhibitor paraoxon was immobilized on the sensing surface via a chelate complex as the recognition element. At first, the conjugate of N-mercaptoundecanoic acid (MUA) with Nalpha,Nalpha-bis (carboxymethyl)-L-lysine (NTA-Lys) was chemisorbed to form a self-assembled monolayer on the surface of the gold electrode of the piezosensor. In the next step, paraoxon-spacer-hexahistidine conjugate was linked to the MUA-Lys-NTA layer via the chelate complex with Ni2+. The paraoxon-modified surface thus obtained was applied for the binding of human butyrylcholinesterase (BChE). Regeneration of the sensing surface was achieved by splitting the chelate complex with EDTA and depositing a fresh layer of Ni2+ followed by addition of the paraoxon-spacer-hexahistidine. In the presence of free inhibitors like diisopropylfluorophosphate (DFP), binding of BChE to the surface-bound paraoxon was decreased. In this way, a competitive affinity assay for organophosphorus compounds was developed. The limit of detection for DFP as a model compound was 10 nmol/l (ca. 2 microg/l). This new concept seems suitable for constructing biosensors for the group-specific detection of cholinesterase-inhibiting substances like insecticides in the field.

Biosensing Techniques↗

PubMed2003

Real time kinetic analysis of the interaction between immunoglobulin G and histidine using quartz crystal microbalance biosensor in solution.

Quartz crystal microbalance (QCM) biosensor integrated in a flow injection analysis (FIA) system was used for the investigation of the specific interaction between immunoglobin G (IgG) and histidine. The histidine was immobilized on the gold electrodes of the piezoelectric crystal using appropriate procedures based on self-assembling of the dithiothreitol (DTT). The specific interaction of the immobilized ligand with IgG in solution was followed as a change in the resonant frequency of the modified crystal and studied in real time without any additional labels. With the mass sensitive biosensor system, the differences in affinity of three different species of IgG: human IgG, goat IgG and mouse IgG were easily distinguished and their respective kinetic rate constants (kass and kdiss) and equilibrium association constants (KA) were determined from the curves of frequency versus time. For the interactions, KA were 2.92 x 10(4), 3.23 x 10(4) and 4.08 x 10(4) M(-1) for human IgG, goat IgG and mouse IgG, respectively.

Adsorption↗

PubMed2003

Optical biosensor consisting of glutathione-S-transferase for detection of captan.

The optical biosensor consisting of a glutathione-S-transferase (GST)-immobilized gel film was developed to detect captan in contaminated water. The sensing scheme was based on the decrease of yellow product, s-(2,4-dinitrobenzene) glutathione, produced from substrates, 1-chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH), due to the inhibition of GST reaction by captan. Absorbance of the product as the output of enzyme reaction was detected and the light was guided through the optical fibers. The enzyme reactor of the sensor system was fabricated by the gel entrapment technique for the immobilized GST film. The immobilized GST had the maximum activity at pH 6.5. The optimal concentrations of substrates were determined with 1 mM for both of CDNB and GSH. The optimum concentration of enzyme was also determined with 100 microg/ml. The activity of immobilized enzyme was fairly sustained during 30 days. The proposed biosensor could successfully detect the captan up to 2 ppm and the response time to steady signal was about 15 min.

Biosensing Techniques↗

PubMed2003

A novel urea sensitive biosensor with extended dynamic range based on recombinant urease and ISFETs.

A novel urea biosensor based on immobilised recombinant urease as sensitive element and ion sensitive field effect transistor as transducer was developed. Recombinant urease from E. coli with an increased Km was photoimmobilised in PVA/SbQ (poly(vinyl alcohol) containing styrylpyridinium) membrane and has demonstrated quite good performance as biosensitive element. Enzymatic field effect transistors based on such a bioselective element were studied in model buffer solutions. This biosensor demonstrated an extended dynamic range up to 80 mM, a quite good reproducibility (standard deviation of the sensor responses was approximately 2.5%, n= 20 for urea concentration 10 mM) and a high stability. Such characteristics fit with the analytical requirements needed for urea control in plasma and liquids used during renal dialysis.

Biosensing Techniques↗

PubMed2003

A new quantitative optical biosensor for protein characterisation.

A new optical biosensor is described based on a dual waveguide interferometric technique. By addressing the waveguide structure with alternate polarisations the optogeometrical properties (density and thickness) of adsorbed protein layers at the sensor (solid)-liquid interface have been determined. Differences in the waveguide mode dispersion between the transverse electric (TE) and transverse magnetic (TM) modes allow unique solutions for adlayer thickness and refractive index to be determined at all stages during the formation process. The technique has been verified using standard protein systems and by comparing the data with published work using X-ray crystallography and neutron reflection techniques. The data obtained was found to be in excellent agreement with previously reported X-ray experiments given that typical film thicknesses for streptavidin layers were in the range 5.5-6.5 nm compared with the short axis crystal structure of between 4.8 and 5.6 nm. The precision of the measurements taken was of the order of 40 pm with respect to adsorbed adlayer thicknesses. This biosensor approach provides measurements of both thickness and density of adlayers to a high precision, simultaneously and in real time enabling detail of the structure and function of proteins to be elucidated. From such data it is possible to obtain information on the orientation, distortion and efficiency of immobilisation procedures as well as the interaction event of interest. The technique is expected to find utility with those interested in protein structure and function. This is an area of growing importance within the life sciences as the demand for quantitative analytical techniques increases with the growth in "proteomics".

Antibodies↗

PubMed2003

Simultaneous determination of L- and D-methotrexate using a sequential injection analysis/amperometric biosensors system.

A sequential injection analysis (SIA) is proposed for the simultaneous determination of L- and D-methotrexate (Mtx) using amperometric biosensors as detectors. A SIA system is proposed due to the highest precision and accuracy and lower consumption of sample and buffer. The amperometric biosensors used as detectors in SIA system were based on L-amino acid oxidase (L-AAOD) or/and L-glutamate oxidase (L-Glox) and horseradish peroxidase (HRP) for the assay of L-Mtx and D-amino acid oxidase (D-AAOD) and HRP for the assay of D-Mtx were selected. The linear concentration ranges are of pmol/l to nmol/l magnitude order, with very low limits of detection. The SIA/biosensors system can be used reliably on-line in synthesis process control, for the simultaneous assay of L- and D-Mtx with a frequency of 34 samples per hour.

Amino Acid Oxidoreductases↗

PubMed2003

A nitric oxide biosensor based on the multi-assembly of hemoglobin/montmorillonite/polyvinyl alcohol at a pyrolytic graphite electrode.

Direct electron transfer of hemoglobin (Hb) can be achieved in a Hb/montmorillonite (MMT)/polyvinyl alcohol multi-assembly at a pyrolytic graphite (PG) electrode. Accordingly, a novel nitric oxide (NO) biosensor is proposed. The reduction of NO is observed at a potential of approximately -783 mV (vs. SCE) at pH 5.5. At optimum pH, this biosensor shows a wide linear range of 1.0x10(-6)-2.5x10(-4) mol/l with a detection limit of 5.0x10(-7) mol/l. The sensor-to-sensor reproducibility is good consideringmacr; a relative standard deviation of 3.5% in five independent determinations at 5.0x10(-5) mol/l NO. The modified electrode is conveniently constructed and durable in long-term operations.

Bentonite↗

PubMed2004

Measuring synchronization in neuronal networks for biosensor applications.

Cultures of neurons can be grown on microelectrode arrays (MEAs), so that their spike and burst activity can be monitored. These activity patterns are quite sensitive to changes in the environment, such as chemical exposure, and hence the cultures can be used as biosensors. One key issue in analyzing the data from neuronal networks is how to quantify the level of synchronization among different units, which represent different neurons in the network. In this paper, we propose a synchronization metric, based on the statistical distribution of unit-to-unit correlation coefficients. We show that this synchronization metric changes significantly when the networks are exposed to bicuculline, strychnine, or 2,3-dioxo-6-nitro-l,2,3,4-tetrahydrobenzoquinoxaline-7-sulphonamide (NBQX). For that reason, this metric can be used to characterize pharmacologically induced changes in a network, either for research or for biosensor applications.

Action Potentials↗

PubMed1997

Amperometric glutamate biosensor based on poly(o-phenylenediamine) film electrogenerated onto modified carbon paste electrodes.

A glutamate biosensor was developed by electropolymerizing o-phenylenediamine on a dehydrogenase-NAD+ modified carbon paste electrode. The amperometric response to glutamate was obtained by means of the electrocatalytic oxidation of the enzymatically produced NADH, at an applied potential close to 0 V (Ag/AgCl). After optimizing carbon paste composition, polymer thickness and operating variables, a linear amperometric response to glutamate was obtained within the concentration range 5.0 x 10(-6)-7.8 x 10(-5) M with a detection limit of 3.8 x 10(-6) M. The biosensor was applied to the determination of glutamate in chicken bouillon cubes. Good accuracy was found with respect to a reference enzymatic spectrophotometric method.

Biosensing Techniques↗

PubMed1997

Development of a new kind of dual modulated QCM biosensor.

To distinguish the mass loading effect from the total frequency change is a problem in the application of a quartz crystal microbalance (QCM) biosensor in the liquid phase. Based on the characteristic damping theory, this paper proposes a new method of dual modulation to solve this problem. Using polyethyleneimine to immobilize anti-SE (staphylococcin enterotoxin) antibody (C2 type), a dual modulated QCM SE biosensor was developed and the experiment proved that it has little cross-reaction with B-type SE. The measuring curve of the sensor was also determined through experiment.

Biosensing Techniques↗

PubMed1998

Acoustic standing-wave enhancement of a fiber-optic Salmonella biosensor.

An enhanced fluorescent fiber-optic biosensor system using ultrasonic concentration of particles and cells has been developed and applied in the detection of Salmonella typhimurium. A biosensor test chamber also serves as an ultrasonic standing-wave cell that allows microspheres or cells to be concentrated in parallel layers or in a column along the axis of the cell. A fiber probe along the axis delivers laser excitation to fluorescent-labeled antibodies of Salmonella and collects the fluorescent signal. The labeled-antibodies themselves do not respond to the ultrasound, but, when attached to Salmonella cells, the Salmonella-antibody complexes can be moved acoustically to the axis of the cell, increasing the fluorescent signal. In a second, more robust, type of immunoassay, the Salmonella-labeled-antibody complexes attach to unlabeled antibodies that have been immobilized on the surface of polystyrene microspheres. This entire structure can be manipulated acoustically and the increase in the fluorescent signal, which can be an order of magnitude, indicates the presence of Salmonella.

Biosensing Techniques↗

PubMed1998

Development of a green fluorescent protein reporter for a yeast genotoxicity biosensor.

A reporter system, constructed for a laboratory screen for new genes involved in DNA repair in the brewer's yeast Saccharomyces cerevisiae, has been developed for use in a genotoxicity biosensor. The strain produces green fluorescent protein (yEGFP) when DNA damage has occurred. yEGFP is codon optimised for yeasts. The reporter does not respond to chemicals which delay mitosis, and responds appropriately to the genetic regulation of DNA repair. Data is presented which demonstrate strain improvements appropriate to biosensor technology: improved signal to noise ratio, ease of data collection and uncomplicated material handling.

Biosensing Techniques↗