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Biomedical subjects

N Jaffrezic-Renault

Publications and source records attributed to N Jaffrezic-Renault.

At least 19 recordsLinked to original sources
PubMed2006

Formaldehyde-sensitive sensor based on recombinant formaldehyde dehydrogenase using capacitance versus voltage measurements.

A new formaldehyde-selective biosensor was constructed using NAD(+)- and glutathione-dependent recombinant formaldehyde dehydrogenase as a bio-recognition element immobilised on the surface of Si/SiO(2)/Si(3)N(4) structure. Sensor's response to formaldehyde was evaluated by capacitance measurements. The calibration curves obtained for formaldehyde concentration range from 10 microM to 20mM showed a broad linear response with a sensitivity of 31 mV/decade and a detection limit about 10 microM. It has been shown that the output signal decreases with the increase of borate buffer concentration and the best sensitivity is observed in 2.5mM borate buffer, pH 8.40. The response of the created formaldehyde-sensitive biosensor has also been examined in 2.5mM Tris-HCl buffer, and the shift to the positive bias of the C(V) curves along with the potential axis has been observed, but the sensitivity of the biosensor in this buffer is decreased dramatically to the value of 2.4 mV/decade.

Aldehyde Oxidoreductases↗
PubMed2006

Formaldehyde assay by capacitance versus voltage and impedance measurements using bi-layer bio-recognition membrane.

A novel formaldehyde sensitive biosensor based on bacterial formaldehyde dehydrogenase (FDH) as a bio-recognition element has been developed. The bio-recognition membrane had bi-layer architecture and consisted of FDH, cross-linked with albumin, and of the cofactor NAD at a high concentration level (first layer). The second layer was a negatively charged Nafion membrane, which prevented a leakage of negatively charged NAD molecules from the bio-membrane. As transducers, gold electrodes SiO(2)/Si/SiO(2)/Ti/Au and electrolyte-insulator-semiconductor Si/SiO(2) (EIS) structures have been used. Changes in capacitance and impedance properties of the bio-recognition membrane have been used for monitoring formaldehyde concentration in a bulk solution. It has been shown that formaldehyde can be detected within a concentration range from 1 microM to 20mM depending on the type of transduction used, with a detection limit of 1 and 100 microM for gold-based and EIS-based transducers, respectively.

Aldehyde Oxidoreductases↗
PubMed2005

Bioelectronic detector with monoamine oxidase for halitosis monitoring.

Methyl mercaptan (MM) is known as one of the major chemicals of halitosis (bad breath). In this study, a bioelectronic gas sensor (bio-detector) for gaseous MM was developed and was applied to measure halitosis in breath. The bio-detector consisted of a Clark-type dissolved oxygen electrode, a monoamine oxidase type-A (MAO-A) immobilized membrane and a reaction unit that had liquid and gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the electrode covered with MAO-A membrane was placed into the liquid compartment as touching to the PTFE diaphragm membrane. In order to amplify the bio-detector output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid as reducing reaction with reagent system, was applied. The results of MM vapor measurements showed the calibration range of the bio-detector for MM vapor was from 0.087 to 11.5 ppm (correlation coefficient: 0.993) and included the human sense of smell level 5 (0.2 ppm). The bio-detector had good selectivity being attributed to enzyme specificity was obtained for several substances (trimethyl amine, ammonia, dimethyl sulfide, etc.). The bio-detector was applied for halitosis measurement. Expired gases in five subjects were sampled every hour and the concentrations of MM in the expired gases were monitored. The output of bio-detector showed behaviour of halitosis level changes in a day such as increasing with passage of time and decreasing after eating.

Biosensing Techniques↗
PubMed2005

Insulator semiconductor structures coated with biodegradable latexes as encapsulation matrix for urease.

A new urea biosensor for clinical applications was obtained by immobilization of urease within different latex polymers functionalized by hydroxy, acetate and lactobionate groups. Responses of these biosensors based on pH-ion-selective field effect insulator-semiconductor (IS) systems to urea additions were evaluated by capacitance measurements. UV-visible spectroscopy was used to check the urease activity in various matrixes. A good retention of the catalytic urease activity in the case of the cationic polymers was observed. In addition, rotating disk electrode experiments were carried out to determine the matrix permeability characteristics. Under optimal conditions, i.e. buffer capacity corresponding to 5 mM phosphate buffer, the urea enzyme insulator semiconductor (ENIS) sensors showed a linear response for urea concentrations in the range 10(-1.5) to 10(-4)M. Furthermore, kinetic parameters for the immobilized urease were obtained from Lineweaver-Burk plot. Clearly, a fast response and a good adhesion for the urease-acetate polymer composite films, prepared without using glutaraldehyde as cross-linking agent was observed.

Absorbable Implants↗
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

Use of competitive inhibition for driving sensitivity and dynamic range of urea ENFETs.

An urea biosensor based on urease-BSA (bovine serum albumin) membrane immobilised on the surface of an ion-sensitive field effect transistor (ISFET) has been studied in a mix buffer solution composed of potassium phosphate, Tris, citric acid and sodium tetraborate. In this mix buffer, the biosensor showed a dynamic larger than the one observed in a phosphate or Tris buffer. Investigation of the individual effect of each component of the buffer solution on the biosensor response has shown that tetraborate anion acts as a strong competitive inhibitor for the hydrolysis reaction of urea catalysed by urease. The biosensor response was investigated in a phosphate buffer with different concentrations of tetraborate anion. The results showed that the apparent constant of Michaelis-Menten, K(m(app)), increases from 4.3 to 79.3 mM, for experiments realised without and with 0.5 mM sodium tetraborate, respectively. The mean value, determined graphically, for the inhibition constant, K(i), was 29 microM. The graphical representation of biosensor calibration curves in semilogarithmic co-ordinates showed that the linear range of the biosensor can be extended up to three orders of magnitude, allowing an urea detection in a concentration range 0-100 mM.

Biosensing Techniques↗
PubMed2002

Urea biosensors based on immobilization of urease into two oppositely charged clays (laponite and Zn-Al layered double hydroxides).

Enzyme-based field effect transistors (ENFETs) for urea determination were developed based on the immobilization of urease within two different clay matrixes, one cationic (Laponite) and the other anionic (layered double hydroxide (LDH)), cross-linked with glutaraldehyde. The biosensor based on the enzyme immobilized in Laponite shows a greater sensitivity and smaller dynamic linear range, because the enzymatic reaction is protected from the effect of the buffer capacity of the outer medium. The apparent Michaelis-Menten constant, Km(app), is quite similar for both biosensors. Inhibition of the enzyme by sodium tetraborate was investigated. Tetraborate acts as a competitive inhibitor for urease in the two different types of clay, the inhibitor effect being stronger for the LDH/urease biosensor. In particular, the maximum limit of the dynamic linear range extends from 1.4 mM in the absence of the inhibitor to 12 mM in the presence of 0.5 mM tetraborate. The Km(app) values in the presence of 0.5 mM tetraborate for Laponite and LDH biomembranes were 10 and 62 mM, respectively. Comparison of the inhibition constant values, Ki 0.16 and 0.05 mM for Laponite and LDH biosensors, respectively, clearly indicates a stronger enzyme-inhibitor interaction in the LDH/urease biomembrane.

Aluminum Silicates↗
PubMed2002

Impedimetric immunosensor using avidin-biotin for antibody immobilization.

The potentialities of an electrodeposited biotinylated polypyrrole film as an immobilisation matrix for the fabrication of impedimetric immunosensors are described. Biotinylated antibody (anti-human IgG), used as a model system, was attached to free biotin groups on the electrogenerated polypyrrole film using avidin as a coupling reagent. This immobilization method allows to obtain a highly reproducible and stable device. The resulting immunosensor has a linear dynamic range of 10-80 ng ml(-1) of antigen and a detection limit of 10 pg ml(-1). Furthermore, this immunosensor exhibited minor loss in response after two regeneration steps.

Avidin↗
PubMed2002

Red blood cells imaging and antigen-antibody interaction measurement.

In the present study the atomic force microscope (AFM) was used to image the surface morphology of red blood cells (RBC) for the first time. The AFM yielded very reproducible images without appreciable modifications of the sample surfaces. In addition to this topographical imaging, we have developed an experimental approach to measure the binding strength between antibody (anti-A), and the RBC antigen A, when reversible bonds between specific molecules such as antigen and antibody mediate the adhesion. The experimental results suggest that the procedure established here may be used for specific antibody detection. This study has also enhanced our understanding under physiological conditions of molecular interaction in particular antigen-antibody.

ABO Blood-Group System↗
PubMed2002

Investigating specific antigen/antibody binding with the atomic force microscope.

The aim of this work is to detect immune complexes without any kind of labelling of each of the immunological species, with a view to create a very sensitive biosensor. This is achieved by using the atomic force microscopy. We have proceeded by imaging the antibody (anti-rabbit IgG) or anti-rabbit IgG moieties adsorbed onto mica surface, before and after incubation of two kinds of antigens: a specific (rabbit IgG) and a non-specific one (sheep IgG). The analysis using the height histograms reveals many interesting features. We propose a general framework for interpreting these analysis, which enables the discrimination between specific and non-specific complexes.

Adsorption↗
PubMed2002

A novel enzyme biosensor for steroidal glycoalkaloids detection based on pH-sensitive field effect transistors.

For the design of a biosensor sensitive to steroidal glycoalkaloids, pH-Sensitive Field Effect Transistors as transducers and immobilised butyrylcholinesterase as a biorecognition element have been used. The total potato glycoalcaloids can be measured by this biosensor in the concentration range 0.5-100 microM with detection limits of 0.5 microM for alpha-chaconine and of 2.0 microM for alpha-solanine and solanidine, respectively. The responses of the developed biosensors were reproducible with a relative standard deviation of about 1.5% and 5% for intra- and inter-sensor responses (both cases, n=10, for an alkaloid concentration of 5 microM), respectively. Moreover, due to the reversibility of the enzyme inhibition, the same sensor chip with immobilised butyrylcholinesterase can be used several times (for at least 100 measurements) after a simple washing by a buffer solution and can be stored at 4 degrees C for at least 3 months without any significant loss of the enzymatic activity.

Alkaloids↗
PubMed2002

Development of enzyme biosensor based on pH-sensitive field-effect transistors for detection of phenolic compounds.

This article describes a biosensor based on pH-sensitive field-effect transistors (pH-FETs) as transducer, and immobilised enzyme tyrosinase as biorecognition element, which was used for the determination of phenolic compounds in water solutions. The biologically active membrane was formed by cross-linking of tyrosinase with bovine serum albumin (BSA) in saturated glutaraldehyde (GA) vapours on the sensitive transducer surface. The main analytical characteristics were studied under different conditions as well as the possibility to optimise these working parameters. Different factors such as the pH of immobilisation, the enzyme loading, the time of exposition to glutaraldehyde vapours were investigated in regards to the influence on sensitivity, limit of detection, dynamic range, and operational and storage stability.

Biosensing Techniques↗
PubMed1998

In vivo voltammetric detection of rat brain lactate with carbon fiber microelectrodes coated with lactate oxidase.

To allow rat brain lactate measurement in vivo, a specific sensor based on a carbon fiber (phi = 30 microns) microelectrode coated with lactate oxidase was prepared. Combined with the differential normal pulse voltammetry measurement method, such a sensor, with a sensitivity of 9.15 +/- 0.91 mA.M-1.cm-2, provided a lactate linear response in concentrations ranging from 0.1 to 2.0 mM. The measurements performed appeared to be essentially insensitive to usual interference caused by the electroactive compounds present in the brain (ascorbic acid and peptides). In vivo detection performed in the cortex of the anesthetized rat led to the determination of a lactate concentration of 0.41 +/- 0.02 mM. Moreover, to validate the results obtained in vivo, an ex vivo determination of the lactate level was also performed in samples of brain tissue, plasma, and cerebrospinal fluid, using both voltammetry and a clinical analyzer with colorimetric-based detection. A good correlation was observed between the sets of data established by both methods.

Animals↗
PubMed1997

Brain glucose: voltammetric determination in normal and hyperglycaemic rats using a glucose microsensor.

Pulsed voltammetry applied to glucose oxidase-coated carbon fibre electrodes (glucose sensor) was used for brain glucose determination in normal and streptozotocin-treated rats (experimental diabetes mellitus). Glucose levels increased in the frontal cortex of diabetic animals compared with the controls (+262%). Glucose levels were also increased in their CSF (+48%) and plasma (+64%), determined in ex vivo conditions. The validity of the glucose sensor determinations, as well as that of the experimental model of diabetes used, was checked using the Beckman glucose analyser and a radioimmunoassay for plasma insulin. Insulin, unlike glucose, was decreased in diabetic animals. The sensor described here ensures precise determinations and is suitable for use in experimental models where alterations in glucose metabolism occur.

Animals↗
PubMed1996

In vivo brain glucose measurements: differential normal pulse voltammetry with enzyme-modified carbon fiber microelectrodes.

The enzyme glucose oxidase was immobilized on the surface of carbon fiber microelectrodes (CFMEs) either by cross-linking in glutaraldehyde vapor or by enzyme entrapment in electropolymerized films of m-phenylenediamine or resorcinol. The cross-linked enzymatic layer was, in the given conditions, covered with an additional membrane of Nafion or cellulose acetate. The prepared glucose sensors were tested using differential normal pulse voltammetry (DNPV, in which the scan comprises successive double pulses ("prepulse and pulse"), the prepulses are of increasing amplitude, and the current measured is the differential of the current existing between each prepulse and pulse). With properly chosen DNPV parameters, the response to glucose presented a peak at a potential of about 1 V versus an Ag/AgC1-reference, owing to the oxidation of enzymatically produced hydrogen peroxide. The calibration curves obtained (peak height/glucose concentration) were linear from 0.3-0.5 up to 1.5-6.5 mM and showed a sensitivity ranging from 1.4 up to 34.5 mA M-1 cm-2, depending on the sensor type. The DNPV response to glucose exhibited an essential insensitivity toward easily oxidizable interfering substances such as ascorbic acid and acetaminophen present at physiological concentrations. Peptides, the interfering species typical of the cerebral medium, were effectively retained by the above additional membranes. Concentration values of glucose in plasma and cerebrospinal fluid, determined in vitro from the DNPV peak height, agreed well with those measured by standard procedures. In the anesthetized rat, extracellular brain concentration of glucose was also monitored during administration of either insulin or glucagon. Under such pharmacological conditions, the changes observed in the peak height were in perfect agreement with the known effects induced by both substances.

Acetaminophen↗
PubMed1996

Performance of urea-sensitive enzyme field effect transistors: influence of the storage conditions.

Urea-sensitive enzyme field effect transistors (ENFETs) were prepared by cross-linking urease with bovine serum albumin in saturated glutaraldehyde vapor on the sensitive surface of a pH-FET. The linear part of the biosensor dynamic range is between 5 x 10(-5) and 10(-3) M of urea. The influence of pH on the sensor response, stability and reproducibility of the urea sensor were examined. The addition of EDTA, glycerol, sodium azide and dithiothreitol in the storage buffer solution was studied. In these specific storage conditions, an increase of sensor sensitivity and stability was observed, which means that the enzyme is inhibited during the immobilisation procedure and can be partially restored. Furthermore such reagents do not affect the operational characteristics of the sensor when working in serum.

Azides↗
PubMedDate not supplied

Sensitive immunodetection through impedance measurements onto gold functionalized electrodes.

This article deals with a direct electrochemical method of detecting antigens using new methods of functionalization of gold electrodes. Based on the reacting ability of gold with sulfhydryl groups, three protocols for the fixation of antibodies have been explored. They are based on either the self-assembling properties of functional thiols bearing long alkyl chains or the possibility of a direct coupling of antibody moieties. Coverage rates as high as 97% can be reached. The analysis of the electrochemical impedance behavior of such layers can lead to a sensitive method for the direct detection of the antibody/antigen interaction. The addition of a redox couple in the tested solution, acting as an amplifier, allowed detection limits for the antigens as low as a few picograms/milliliter to be reached.

Antibodies↗