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Biomedical subjects

C Martelet

Publications and source records attributed to C Martelet.

At least 19 recordsLinked to original sources
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

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↗
PubMed2004

Contribution of the comonomers to the bulk and surface properties of methacrylate copolymers.

Relationships between formulation, bulk properties, and surface properties are investigated on series of copolymers prepared with hydroxyethylmethacrylate (HEMA), methylmethacrylate (MMA), and ethylmethacrylate (EMA) monomers, and on the homopolymers PMMA and PHEMA. The bulk water content, swelling ratio, and static (sessile drop and captive bubble) and dynamic (Wilhelmy plate technique) contact angles and the electrokinetic potential (streaming potential) are measured. The bulk water content and swelling ratio of HEMA copolymers are proportional to the amount of HEMA and are linearly correlated to the contact angle hysteresis. Periodic instabilities in the wetting cycles, similar to Haines jumps, are observed with HEMA copolymers and support a bidirectional relaxation of the hydrophilic groups respectively towards external water and capillary water. The origin of the electrokinetic potential of these nonionizable polymers is attributed to specific adsorption of [Formula: see text] ions. Its dependence on surface hydrophobicity and statistical length of the side-chains is interpreted in terms of the properties of water molecules near the interface.

Journal Article↗
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

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↗
PubMed2000

Development of highly selective and stable potentiometric sensors for formaldehyde determination.

Two types of biosensors selective to formaldehyde have been developed on the basis of pH-sensitive field effect transistor as a transducer. Highly or partially purified alcohol oxidase (AOX) and the permeabilised cells of methylotrophic yeast Hansenula polymorpha (as a source of AOX) have been used as sensitive elements. The response time in steady-state measurement mode is in the range of 10-60 s for the enzyme-based sensors and 60-120 s for the cell-based sensor. When measured in kinetic mode the response time of all biosensors developed was less than 5 s. The linear dynamic range of the sensor output signals corresponds to 5-200 mM formaldehyde for highly and partially purified alcohol oxidase, and 5-50 mM formaldehyde for the cells. The operational stability of the biosensors is not less than 7 h, and the relative standard deviation of intra-sensor response is approximately 2 and 5% for the enzyme- and cell-based sensors, respectively. When stored at 4 degrees C, the enzyme and cell sensor responses have been found stable for more than 60 and 30 days, respectively. Both types of biosensors demonstrate a high selectivity to formaldehyde with no potentiometric response to primary alcohols, including methanol, or glycerol and glucose. The possible reasons of such unexpected high selectivity of AOX-based FET-sensors to formaldehyde are discussed. The influence of the biomembrane composition and the effect of different buffers on the sensor response to formaldehyde are also discussed.

Alcohol Oxidoreductases↗
PubMed1999

Application of enzyme field-effect transistors for determination of glucose concentrations in blood serum.

Glucose-sensitive enzyme field effect transistors (ENFETs) modified by an additional Nafion membrane have been developed and used for diluted blood samples analysis. The ENFET was used in the linear portion of the calibration curve up to 1.5 mM glucose in a model solution, which corresponds with up to 60 mM glucose in the undiluted samples (dilution 1:40). The high linearity of the Grans curve (factor of linearity is 1.03) obtained by the method of standard additions indicates the high precision of analysis. Glucose concentrations in different blood serum samples determined by ENFETs were compared with those measured by the commercial analyzer 'Eksan-G' and colorimetric method ('Diagluc' enzymatic kit), and good correlation between these methods was revealed. The high reproducibility and operational stability of the biosensor developed were demonstrated.

Animals↗
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↗
PubMed1995

Under buffer SFM observation of immunospecies adsorbed on a cyano grafted silicon substrate.

Scanning force microscopy (SFM) in contact mode and in liquid medium has been employed to study immunospecies layers adsorbed on a silicon wafer. The silicon wafer has been grafted with a cyanosilane monolayer in order to create a surface with strong adhesive properties which prevent proteins being swept by the scan of the SFM tip. The force curves reveal that the adhesive force has been increased by a factor six without roughness modification (< 1 nm). After the incubation of the surface in a monoclonal antibody (mouse anti-human alpha-fetoprotein IgG) solution, SFM surface images suggest an homogeneous layer composed by ellipsoidal objects (40-60 nm in diameter, 6-13 nm in height). The substrate was moreover incubated in an antigenic solution (human alpha-fetoprotein): SFM images reveal that proteins have been added onto the antibody layer.

Antibodies, Monoclonal↗
PubMed1993

Study of immunoglobulin G thin layers obtained by the Langmuir-Blodgett method: application to immunosensors.

Nowadays, immunosensors play a leading part in the field of bioanalytical chemistry research. As with any biosensor, they need appropriate transducers and a suitable technique to immobilize the active biocomponents. In this study, two transduction modes were chosen: mass effects (quartz microbalance measurements) and geometric and dielectric effects (capacitance measurements). The Langmuir-Blodgett (LB) method appears to be quite suitable for generating biospecific surfaces. This work has focused on the detection of staphylococcal enterotoxin B, the corresponding antibody being immobilized at the surface of fatty acids by a variant of the LB method. The composition of the film and the nature of antibody-fatty acid interactions were studied by means of the two transducers mentioned above. FTIR (Fourier transform infra-red) spectroscopy and protein diagnostic assay. Influence of several parameters (pH, ionic strength, transfer pressure, antibody concentration in the subphase) was investigated. The immobilization rate reached its maximum when experimental conditions allowed optimal electrostatic interactions. In this case, the quartz crystal microbalance response, in air, reached 55 Hz per monolayer of immobilized immunoglobulin G and the equivalent capacitance variation, measured in liquid media, was around 300 pF cm-2. Activity of the biospecific LB films, when binding enterotoxin, was checked by the classical ELISA (enzyme immuno-linked assay) technique.

Antigen-Antibody Reactions↗