User-friendly one-step disposable signal-on bioassay for glyphosate detection in water samples

The onsite detection of glyphosate requires an easy-to-handle, low-cost and disposable assay for untrained users as requested by the ASSURED guidelines. A new strategy based on the expression of fusion proteins is proposed here. A glyphosate oxidase derived from Bacillus subtilis and the 6E10 variant of the dye peroxidase from Pseudomonas putida, both fused with the carbohydrate binding module (CBM) 3a from Clostridium thermocellum, were designed and expressed, leading to GlyphOx-CBM and 6E10-CBM. Cell lysates were used to immobilise both enzymes on cotton buds' heads without any purification. The cotton buds exhibit glyphosate oxidase activity when dipped into a glyphosate-contaminated water sample containing the 6E10-CBM chromogenic substrates. The chromophore could be quantified both in the solution and on the cotton buds' heads. Photography followed by image analysis allows to detect glyphosate with a linear range of 0.25-2.5 mM and a limit of detection (LoD) of 0.12 mM. When the chromogenic substrates are replaced by luminol, the chemiluminescence reaction allows the detection of glyphosate with a linear range of 2-500 μM and a LoD of 0.45 μM. No interference was observed using glyphosate analogues (glycine, sarcosine, aminomethylphosphonic acid) or other herbicides used in a mixture. Only cysteine was found to inhibit 6E10-CBM. Two river waters spiked with glyphosate lead to recoveries of 64-131%. This work describes a very easy-to-handle and inexpensive signal-on bioassay for glyphosate detection in real surface water samples.

Membrane Fluidity as a New Means to Selectively Target Cancer Cells with Fusogenic Lipid Carriers

Lipid-based carriers such as liposomes represent one of the most advanced classes of drug delivery systems. Their clinical success relies on their composition, similar to that of the cell membrane. Their cellular specificity often relies on a ligand-receptor interaction. Although differences in the physicochemical properties of the cell membrane between tumor and nontumor cells have been reported, they are not systematically used for drug delivery purposes. In this report, a new approach was developed to ensure selective targeting based on physical compatibility between the target and the carrier membranes. By modulating the liposome composition and thus its membrane fluidity, we achieved selective targeting on four cancer cell lines of varying aggressiveness. Furthermore, using membrane-embedded and inner core-encapsulated fluorophores, we assessed the mechanism of this interaction to be based on the fusion of the liposome with the cell membranes. Membrane fluidity is therefore a major parameter to be considered when designing lipid drug carriers as a promising, lower cost alternative to current targeting strategies based on covalent grafting.

Innovative Electrochemical Screening Allows Transketolase Inhibitors to Be Identified

Transketolases (TKs) are ubiquitous thiamine pyrophosphate (TPP)-dependent enzymes of the nonoxidative branch of the pentose phosphate pathway. They are considered as interesting therapeutic targets in numerous diseases and infections (e.g., cancer, tuberculosis, malaria), for which it is important to find specific and efficient inhibitors. Current TK assays require important amounts of enzyme, are time-consuming, and are not specific. Here, we report a new high throughput electrochemical assay based on the oxidative trapping of the TK-TPP intermediate. After electrode characterization, the enzyme loading, electrochemical protocol, and substrate concentration were optimized. Finally, 96 electrochemical assays could be performed in parallel in only 7 min, which allows a rapid screening of TK inhibitors. Then, 1360 molecules of an in-house chemical library were screened and one early lead compound was identified to inhibit TK from E. coli with an IC₅₀ of 63 μM and an inhibition constant ( K_I) of 3.4 μM. The electrochemical assay was also used to propose an inhibition mechanism.

Human Skin 3D Bioprinting Using Scaffold-Free Approach

Organ in vitro synthesis is one of the last bottlenecks between tissue engineering and transplantation of synthetic organs. Bioprinting has proven its capacity to produce 3D objects composed of living cells but highly organized tissues such as full thickness skin (dermis + epidermis) are rarely attained. The focus of the present study is to demonstrate the capability of a newly developed ink formulation and the use of an open source printer, for the production of a really complete skin model. Proofs are given through immunostaining and electronic microscopy that the bioprinted skin presents all characteristics of human skin, both at the molecular and macromolecular level. Finally, the printability of large skin objects is demonstrated with the printing of an adult-size ear.

Multiplex cell microarrays for high-throughput screening

Microarray technology was developed in the early 1990s to measure the transcription levels of thousands of genes in parallel. The basic premise of high-density arraying has since been expanded to create cell microarrays. Cells on chip are powerful experimental tools for high-throughput and multiplex screening of samples or cellular functions. Miniaturization increases assay throughput while reducing both reagent consumption and cell population heterogeneity effect, making these systems attractive for a wide range of assays, from drug discovery to toxicology, stem cell research and therapy. It is usual to functionalize the surface of a substrate to design cell microarrays. One form of cell microarrays, the transfected cell microarray, wherein plasmid DNA or siRNA spotted on the surface of a substrate is reverse-transfected locally into adherent cells, has become a standard tool for parallel cell-based analysis. With the advent of technology, cells can also be directly spotted onto functionalized surfaces using robotic fluid-dispensing devices or printed directly on bio-ink material. We are providing herein an overview of the latest developments in optical cell microarrays allowing high-throughput and high-content analysis.

Adding Biomolecular Recognition Capability to 3D Printed Objects

Three-dimensional (3D) printing technologies will impact the biosensor community in the near future, at both the sensor prototyping level and the sensing layer organization level. The present study aimed at demonstrating the capacity of one 3D printing technique, digital light processing (DLP), to produce hydrogel sensing layers with 3D shapes that are unattainable using conventional molding procedures. The first model of the sensing layer was composed of a sequential enzymatic reaction (glucose oxidase and peroxidase), which generated a chemiluminescent signal in the presence of glucose and luminol. Highly complex objects with assembly properties (fanciful ball, puzzle pieces, 3D pixels, propellers, fluidic and multicompartments) with mono-, di-, and tricomponents configurations were achieved, and the activity of the entrapped enzymes was demonstrated. The second model was a sandwich immunoassay protocol for the detection of brain natriuretic peptide. Here, highly complex propeller shape sensing layers were produced, and the recognition capability of the antibodies was elucidated. The present study opens then the path to a totally new field of development of multiplex sensing layers, printed separately and assembled on demand to create complex sensing systems.

Development and Validation of a Fully Automated Platform for Extended Blood Group Genotyping

Thirty-five blood group systems, containing >300 antigens, are listed by the International Society of Blood Transfusion. Most of these antigens result from a single nucleotide polymorphism. Blood group typing is conventionally performed by serology. However, this technique has some limitations and cannot respond to the growing demand of blood products typed for a large number of antigens. The knowledge of the molecular basis of these red blood cell systems allowed the implementation of molecular biology methods in immunohematology laboratories. Here, we describe a blood group genotyping assay based on the use of TKL immobilization support and microarray-based HIFI technology that takes approximately 4 hours and 30 minutes from whole-blood samples to results analysis. Targets amplified by multiplex PCR were hybridized on the chip, and a revelation step allowed the simultaneous identification of up to 24 blood group antigens, leading to the determination of extended genotypes. Two panels of multiplex PCR were developed: Panel 1 (KEL1/2, KEL3/4; JK1/2; FY1/2; MNS1/2, MNS3/4, FY*Fy et FY*X) and Panel 2 (YT1/2; CO1/2; DO1/2, HY+, Jo(a+); LU1/2; DI1/2). We present the results of the evaluation of our platform on a panel of 583 and 190 blood donor samples for Panel 1 and 2, respectively. Good correlations (99% to 100%) with reference were obtained.

Peroxide detected in imidazolium-based ionic liquids and approaches for reducing its presence in aqueous and non-aqueous environments

Peroxide species appearing in imidazolium-based ionic liquids could be removed by salen–manganese complexes or the enzyme catalase.

Microarrays in blood group genotyping

Thirty-five blood group systems, containing more than 300 antigens, are listed by the International Society of Blood Transfusion (ISBT). Most of these antigens result from a single-nucleotide polymorphism (SNP). Blood group typing is conventionally carried out by serology. However, this technique has certain limitations and cannot respond to the growing demand for blood products typed for a large number of antigens. Here we describe a blood group genotyping assay, from genomic DNA extraction from whole-blood samples to results. After DNA extraction, the on-chip test is based on the hybridization of targets beforehand amplified by multiplex polymerase chain reaction, followed by a revelation step allowing the simultaneous identification of up to 24 blood group antigens and leading to the determination of extended genotypes.

Directed evolution of a formate dehydrogenase for increased tolerance to ionic liquids reveals a new site for increasing the stability

The formate dehydrogenase (FDH) from Candida boidinii is a well-known enzyme in biocatalysis for NADH regeneration. Nevertheless, it has low activity in a water-miscible ionic liquid (1,3-dimethylimidazolium dimethyl phosphate, [MMIm][Me2 PO4 ]). In this work, this enzyme was subjected to directed evolution by using error-prone PCR, and a mutant (N187S/T321S) displaying higher activity was obtained following selection based on the formazan-based colorimetric assay. The mutation N187S is responsible for improved activity both in aqueous solution and in [MMIm][Me2 PO4 ], through an enhancement of the kcat value by a factor of 5.8. Fluorescence experiments performed in the presence of a quenching agent revealed that the mutant does not unfold in the presence of 50 % (v/v) [MMIm][Me2 PO4 ] whereas the wild-type enzyme does. Molecular modelling revealed that the mutation is located at the monomer-monomer interface and causes an increase in the pKa of residue E163 from 4.8 to 5.5. Calculation of the pKa of this residue in other microbial FDHs showed that thermostable FDHs have a highly basic glutamate at this position (pKa up to 6.2). We have identified a new site for improving FDH thermostability and tolerance to ionic liquids, and it is linked to the local charge of the enzymes in this class.

Rapid electrochemical screening of NAD-dependent dehydrogenases in a 96-well format

The electrochemical detection of dehydrogenase activity in crude cell lysates is performed simultaneously using 96 carbon electrodes modified with electrografted phenazines. The method is applied to the screening of a library of formate dehydrogenase mutants obtained by directed evolution.

Multiplex microarray ELISA versus classical ELISA, a comparison study of pollutant sensing for environmental analysis

The present study describes the development, optimization and performance comparison of three ELISAs and one multiplex immunoassay in a microarray format. The developed systems were dedicated to the detection of three different classes of pollutants (pesticide, explosive and toxin) in water. The characteristics and performances of these two types of assays were evaluated and compared, in order to verify that multiplex immunoassays can replace ELISA for multiple analyte sensing. 2,4-Dichlorophenoxyacetic acid, 2,4,6-trinitrotoluene and okadaic acid were chosen as model targets and were immobilized in classical microtiter plate wells or arrayed at the surface of a microarray integrated within a classical 96-well plate. Once optimized, the classical ELISAs and microarray-based ELISA performances were evaluated and compared in terms of limit of detection, IC50, linearity range and reproducibility. Classical ELISAs provided quite good sensitivity (limit of detection down to 10 μg L(-1)), but the multiplex immunoassay was proven to be more sensitive (limit of detection down to 0.01 μg L(-1)), more reproducible and an advantageous tool in terms of cost and time expenses. This multiplex tool was then used for the successful detection of the three target molecules in spiked water samples and achieved very promising recovery rates.

A 96-well electrochemical method for the screening of enzymatic activities

The rapid electrochemical screening of enzyme activities in bioelectronics is still a challenging issue. In order to solve this problem, we propose to use a 96-well electrochemical assay. This system is composed of 96 screen-printed electrodes on a printed circuit board adapted from a commercial system (carbon is used as the working electrode and silver chloride as the counter/reference electrode). The associated device allows for the measurements on the 96 electrodes to be performed within a few seconds. In this work, we demonstrate the validity of the screening method with the commercial laccase from the fungus Trametes versicolor. The signal-to-noise ratio (S/N) is found to be the best way to analyze the electrochemical signals. The S/N follows a saturation-like mechanism with a dynamic linear range of two decades ranging from 0.5 to 75 ng of laccase (corresponding to enzymatic activities from 62 × 10(-6) to 9.37 × 10(-3) μmol min(-1)) and a sensitivity of 3027 μg(-1) at +100 mV versus Ag/AgCl. Laccase inhibitors (azide and fluoride anions), pH optima, and interfering molecules could also be identified within a few minutes.

Shrinking hydrogel-DNA spots generates 3D microdots arrays

This report describes a straightforward approach for the achievement of sub-100 micrometers size hydrogel dots supporting DNA immobilization. Hydrogel-DNA spots are arrayed and UV-crosslinked on PolyShrink, an innovative polymer material having the remarkable property of isotropically shrinking under high temperature. Curing the microarray enables then spot miniaturization, resulting in 6 µm thick and 60 µm wide hydrogel dots in which oligonucleotides are immobilized in a 3D hydrophilic environment. The probe immobilization within the hydrogel network and its capacity to detect targets specifically and quantitatively is demonstrated using chemiluminescent as well as colorimetric detection techniques. The hydrogel material improves probe accessibility within the spot, leading to an enhanced sensitivity.

Luciferin incorporation in the structure of acrylic microspheres with subsequent confinement in a polymeric film: A new method to develop a controlled release-based biosensor for ATP, ADP and AMP

The controlled release of coreactants at the sensing tip of a biosensor is a possible approach to develop self-contained devices. For luciferin which is a firefly luciferase cosubstrate, a new method of retention is evaluated. The two-step procedure consists of incorporating the substrate in acrylic microspheres during their formation, these last being then confined in a PVA SbQ film. When associated with a compartmentalised trienzymatic sequence (adenylate kinase, creatine kinase and luciferase), such a complex matrix ensures the internal delivery of the cosubstrate in the enzymatic microenvironment at a controlled rate. For the three adenylic nucleotides (ATP, ADP and AMP), the self-containment working time is 3 h of continuous and reproducible assays. The sensitivity of the fibre optic biosensor represents, for ATP, 30% of that obtained when luciferin is supplied in solution whereas for ADP and AMP, the values are about 80% of the reference ones.

Polymer adhesive surface as flexible generic platform for multiplexed assays biochip production

The present report describes the integration and application possibilities of a new microarray concept based on adhesive surface. The method was shown to enable the straightforward production of 384 and 1536-well plates modified with 100 and 25 spots per well, respectively. Such in-well densities were only possible thanks to the fabrication process which implies first the deposition of the microarray on a flat adhesive surface and then its assembly with bottomless 384 or 1536-well plates. The concept was also confronted to various applications such as oligonucleotide detection, localised cell culture onto spotted adhesion proteins and immobilisation of peptide or active antibodies for immunoassays. In the particular case of immunotesting, the study focused on liver diseases diagnosis and more particularly on the detection of either one liver cancer marker, the alpha-fetoprotein, or the detection of Hepatitis C Virus infection. In every cases, interesting performances were obtained directly in crude patient serum, proof of the robust and generic aspect of the platform.

SU-8-carbon composite as conductive photoresist for biochip applications

A composite photoresist has been developed for the direct photopatterning of electrodes useful as biochip substrates. The material is composed of SU-8 polymer added with graphite carbon filler which enables patterning of conductive thin films (22 μm) on both glass substrate and transparency flexible film with a standard UV photolithography protocol. The resolution obtained using the conductive composite compared well with the bare resist, with lateral resolutions of 5 and 10 μm for bare and conductive resists, respectively. The obtained electrodes, after an electrochemical pre-treatment, exhibited very good electrochemical behaviors, opening the path to various electrochemical detections and grafting possibilities. In order to demonstrate the potentialities of the developed material in the biosensors and biochips field, DNA probes were electrografted, using diazonium chemistry, directly at the composite photoresist surface. Target oligonucleotide interactions were detected using chemiluminescent labeling and a satisfactory detection limit of 0.25 nM target sequence was demonstrated with a detection ranging over three orders of magnitude.

Adhesive microarrays for multipurpose diagnostic tools

We are reporting here a new technology for the straightforward production of integrated microarrays. The approach is based on the use of adhesive supports enabling (i) the immobilization of biomolecules as microarrays (up to 2500 spots per cm(2)) and (ii) the easy assembly of these microarrays with complex 3D structures such as 96-well bottomless microplates or polymer and glass microfluidic networks. The analytical performances of the system were demonstrated for sandwich protein detection (C-reactive protein) and hybridization assays, both in classical 96-well microplate format and microfluidic environment.

Homogeneous assays using aptamers

Aptamers are DNA or RNA oligonucleotides that can bind with high affinity and specificity to a wide range of targets such as proteins, metal ions or pathogenic microorganisms. Soluble aptamers and aptazymes have been used as sensing elements for developing homogeneous assays in a solution phase, the whole sensing process being carried out in a homogeneous solution. Contrary to most conventional heterogeneous assays that are time-consuming and labor-intensive, aptamer-based homogeneous assays are simple, easy-to-perform, rapid and do not require immobilization nor washing steps. To our knowledge, this review is the first entirely dedicated to aptamer-based homogeneous assays. Optical detection appears as the most developed technique. Colorimetry represents the simplest sensing mode that occupies a very important position among aptamer-based assays, involving gold nanoparticle aggregation (with unmodified or aptamer-modified gold NPs), the formation of HRP-mimicking DNAzyme with hemin, dye displacement or interactions with a cationic polymer. Fluorescence that is highly sensitive offers the most developed detection mode. Aptamers can be labeled or not, to give rise to turn-on or usually less sensitive turn-off fluorescent assays. Newly reported and thus less developed non-conventional magnetic resonance imaging (MRI) and electrochemistry also recently appeared in the literature, thrombin still remains the main detected target. Homogeneous assays based on aptazyme, an aptamer sequence connected to a known ribozyme motif, are also described in this review, involving optical detection, by colorimetry or fluorescence.

Automated oligonucleotide solid-phase synthesis on nanosized silica particles using nano-on-micro assembled particle supports

This article describes an original strategy to enable solid-phase oligodeoxyribonucleotide (ODN) synthesis on nanosized silica particles. It consists of the reversible immobilization of silica nanoparticles (NPs) on micrometric silica beads. The resulting assemblies, called nano-on-micro (NOM) systems, are well adapted to ODN synthesis in an automated instrument. First, NPs are derivatized with OH functions. For NOM assembly preparation, these functions react with the silanols of the microbeads under specific experimental conditions. Furthermore, OH groups allow ODN synthesis on the nanoparticles via phosphoramidite chemistry. The stability of the NOM assemblies during ODN solid-phase synthesis is confirmed by scanning and transmission electron microscopy (SEM and TEM, respectively), together with dynamic light scattering analyses. Then, the release of ODN-functionalized nanoparticles is performed under mild conditions (1% NH(4)OH in water, 1 h, 60 degrees C). Our technique provides silica nanoparticles well functionalized with oligonucleotides, as demonstrated by hybridization experiments conducted with the cDNA target.

Two-dimensional supramolecular assemblies involving neoglycoplipids: Self-organization and insertion properties into Langmuir monolayers

In nature, interfacial molecular recognition and chirality are of fundamental significance for the construction of biological assemblies. Lipid monolayers at liquid interface can be used as biomimetic models for studying molecular interactions in such assemblies. In this article, we will focus on the use of Langmuir monolayers for studying self-organization and insertion properties of several neoglycolipids. Two types of glycolipids have been considered, one in the context of the analysis of glycoconjugates of biological relevance, and one dealing with the ability of some glycoprobes to insert into a monolayer in relation with their efficiency for serving as membrane imaging systems.

Chelating Langmuir-Blodgett film: a new versatile chemiluminescent sensing layer for biosensor applications

The present study reports the achievement of a new chemiluminescent sensing layer able to simultaneously (i) play an active role on ligand immobilization and (ii) serve as a catalyst in detection processes for label-free biosensor applications. This new type of active Langmuir-Blodgett (LB) monolayer has been designed by using a chelating lipid (Ni-NTA-DOGS). Thanks to the chelated metallic cation, this peculiar lipid exhibits luminol chemiluminescence catalysis properties in the presence of hydrogen peroxide. Upon biomolecule interaction through imidazole ring chelation (mediated by the metallic cation bound to the lipid headgroup), the chemiluminescent signal can be modulated. The first chemiluminescent signal acquisition experiments have shown a strong and homogeneous signal of the chelating layer. Upon histamine interactions, a histidine derivative used as a marker of fresh food quality, we succeeded in obtaining as a proof of concept a chemiluminescent signal variation without any derivatization of the target molecule. This signal variation was shown to be directly correlated to the histamine concentration with a limit of detection of 2 microg/mL.

"Print-n-Shrink" technology for the rapid production of microfluidic chips and protein microarrays

An innovative method for the production of microfluidic chips integrating protein spots is described. The technology, called "Print-n-Shrink", is based on the screen-printing of a microfluidic design (using a dielectric ink) onto Polyshrink polystyrene sheets. The initial print which has a minimum size of 15 microm (height) x 230 microm (width) is thermally treated (30 seconds, 163 degrees C) to shrink and generate features of 85 microm (height) x 100 microm (width). Concomitantly, proteins such as monoclonal antibodies or cellular adhesion proteins are spotted onto the Polyshrink sheets and shrunk together with the microfluidic design, creating a complete biochip integrating both complex microfluidic designs and protein spots for bioanalytical applications.

Protein-diazonium adduct direct electrografting onto SPRi-biochip

A direct protein immobilization method for surface plasmon resonance imaging (SPRi) gold chip arraying is exposed. The biomolecule electroaddressing strategy, previously demonstrated by our team on carbon surfaces, is here valuably involved and adapted to create a straightforward and efficient protein immobilization process onto SPRi-biochips. The proteins, modified with an aryl-diazonium adduct, are addressed to the SPRi chip surface through the electroreduction of the aryl-diazonium. The biomolecule deposition was followed through SPRi live measurements during the electrografting process. A specially designed setup enabled us to directly observe the mass increasing at the sensor surface while the proteins were electrografted. A pin electrospotting method, allowing the achievement of distinct sensing layers on gold SPRi-biochips, was used to generate microarray biochips. The integrity of the immobilized proteins and the specificity of the detection, based on antigen/antibody interactions, were demonstrated for the detection of specific antibodies and ovalbumin. The SPRi detection limit of ovalbumin using the electroaddressing of anti-ovalbumin IgG was compared with two other immobilization procedures, cystamine-glutaraldehyde self-assembled monolayer and pyrrole, and was found to be a decade lower than these ones (100 ng/mL, i.e., 2 nM).

New electrochemiluminescent biosensors combining polyluminol and an enzymatic matrix

Performant reagentless electrochemiluminescent (ECL) (bio)sensors have been developed using polymeric luminol as the luminophore. The polyluminol film is obtained by cyclic voltammetry (CV) on a screen-printed electrode either in a commonly used H(2)SO(4) medium or under more original near-neutral buffered conditions. ECL responses obtained after performing polymerization either at acidic pH or at pH 6 have been compared. It appears that polyluminol formed in near-neutral medium gives the best responses for hydrogen peroxide detection. Polymerization at pH 6 by cyclic voltammetry gives a linear range extending from 8 x 10(-8) to 1.3 x 10(-4) M H(2)O(2) concentrations. Based on this performant sensor for hydrogen peroxide detection, an enzymatic biosensor has been developed by associating the polyluminol film with an H(2)O(2)-producing oxidase. Here, choline oxidase (ChOD) has been chosen as a model enzyme. To develop the biosensor, luminol has been polymerized at pH 6 by CV, and then an enzyme-entrapping matrix has been formed on the above modified working electrode. Different biological (chitosan, agarose, and alginate) and chemical (silica gels, photopolymers, or reticulated matrices) gels have been tested. Best performances have been obtained by associating a ChOD-immobilizing photopolymer with the polyluminol film. In this case, choline can be detected with a linear range extending from 8 x 10(-8) to 1.3 x 10(-4) M.

Straightforward protein immobilization using redox-initiated poly(methyl methacrylate) polymerization

Rigid poly(methyl methacrylate) (PMMA) biochips directly modified with active protein spots were obtained, using a redox-initiated PMMA polymerization process. The protein immobilization mechanism is believed to be a combination of both a covalent binding through transient amino acid radical generation and a direct entrapment of the biomolecules in the PMMA polymer. Three different immunoassays (binding, capture, and sandwich) were performed using the developed system, and really promising limits of detection (160-200pg/mL) were obtained, demonstrating a novel straightforward route to fabricate plastic biochips.

Functionalization of luminescent aminated particles for facile bioconjugation

For labeling proteins (streptavidin and fibronectin) by luminescent aminated nanoparticles, an interesting strategy that requires neither activation nor chemical pre- or post-treatment was explored. Because biomolecules are easily rendered luminescent after reaction with organic dyes carrying isothiocyanate moiety, phenylene diisothiocyanate (DITC) was used for covalently binding proteins onto luminescent hybrid gadolinium oxide nanoparticles whose ability to combine imaging and therapy was recently demonstrated.

Microfluidic biochip for chemiluminescent detection of allergen-specific antibodies

Protein microarrays for allergen-specific antibodies detection were integrated in microfluidic chips, with imaging chemiluminescence as the analytical technique. This paper demonstrates the feasibility of miniaturized chemiluminescent ELISA by presenting rapid, reproducible and sensitive detection of protein antibodies using microfluidics. Three different proteins, beta-lactoglobulin, peanut lectin and human IgG were immobilized via a "macromolecules to polydimethylsiloxane elastomer (PDMS) transfer" protocol and used as capturing agent for the detection of specific antibodies. A convenient and reversible procedure was used to bond the PDMS microarray substrate to complimentary SU-8/glass microfluidic reaction chambers. The hydrodynamic behaviours of the three proteins interactions within the micro-chambers were investigated to select the most efficient flowing parameters (come to terms with the assay time and performances). The use of optimized conditions led to the concomitant detection of three specific antibodies at pM level in 300 microL and using 6 min sample incubation time. Finally, sera from allergic patients were assayed using the microfluidic device modified with apple hazelnut and pollen allergen. The results obtained compared favourably with those obtained with the classical Pharmacia CAP system.

Cylinder-shaped conducting polypyrrole for labelless electrochemical multidetection of DNA

A new multidetection biosensor has been developed using the electrochemical properties of cylinder-shaped conducting polypyrrole grown on miniaturized graphite electrodes. Our objective was to conceive a sensitive, labelless and real-time DNA sensor for biomedical diagnosis. In a first step, copolymers bearing both ferrocene redox markers and oligonucleotide probes were selectively electro-addressed on microchip electrodes. Then, the study of their voltammetric response upon the addition of DNA targets revealed that the hybridization was efficiently transduced through the variation of ferrocene oxidation intensity. Using this technique, a good selectivity between Human Immunodeficiency Virus and Hepatitis B Virus targets was obtained. It was indeed possible to directly follow the hybridization. Complementary DNA detection limit reached 100 pM (3 fmol in 30 microL), which represents a good performance for such a practical, labelless and real-time sensor.

Electro-chemiluminescent biosensing

The present review draws a general picture of the bioanalytical applications of electro-chemiluminescent reactions (ECL). Only the two main ECL reactions-i.e. the luminol-based and Ru(bpy)(3)(2+)-based reactions-are considered for application in the fields of enzyme biosensors, immunochemical biosensors, DNA biosensors, and biochips. The mechanism, principle, and experimental conditions of these two reactions are described. Then, for each category of analytical tools, experimental set-ups and performances are presented and discussed.