Herbicides are the most widely used class of pesticides in the world. Their intensive use raises the question of their harmfulness to the environment and human health. These pollutants need to be detected at low concentrations, especially in water samples. Commonly accepted analytical techniques (HPLC-MS, GC-MS, ELISA tests) are available, but these highly sensitive and time-consuming techniques suffer from high cost and from the need for bulky equipment, user training and sample pre-treatment. Biosensors can be used as complementary earlywarning systems that are less sensitive and less selective. On the other hand, they are rapid, inexpensive, easy-to-handle and allow direct detection of the sample, on-site, without any further step other than dilution. This review focuses on enzyme- and cell- (or subcellular elements) based biosensors. Different enzymes (such as tyrosinase or peroxidase) whose activity is inhibited by herbicides are presented. Photosynthetic cells such as algae or cyanobacteria are also reported, as well as subcellular elements (thylakoids, chloroplasts). Atrazine, diuron, 2,4-D and glyphosate appear as the most frequently detected herbicides, using amperometry or optical transduction (mainly based on chlorophyll fluorescence). The recent new WSSA/HRAC classification of herbicides is also included in the review.

The discovery of luminol electrogenerated chemiluminescence (ECL) at carbon electrodes in the presence of hydrogen peroxide by Sakura in 1992 and the enhanced ECL of ruthenium-(2,2′-bipyridyl)32+ complex (Ru(bpy)32+) in the presence of reduced nicotinamide adenine dinucleotide (NADH) by Jameison in 1996 opened the way for ECL-based enzyme assays: the activity of oxidases that generate hydrogen peroxide and the one of dehydrogenases that produce NADH could be measured thanks to light emission of luminol or Ru(bpy)32+, respectively. This chapter reviews the important achievements in ECL-based biosensing systems since nearly 20 years. Numerous systems involving, first luminol or Ru(bpy)32+ as soluble ECL emitters, then immobilized on an electrode surface are described, distinguishing bioassays and biosensors. The introduction of nanomaterials such as nanoparticles (NPs) that act as ECL enhancers with some of them having their own ECL properties (e.g. quantum dots) are presented. The combination of several nanomaterials into the so-called nanocomposites offers new opportunities in the field of enzyme-based ECL bioassays and biosensors. Finally, future trends in bipolar electrochemistry and ratiometric assays are presented.

This paper reports on electrochemiluminescent sensors and biosensors based on polyluminol/hydrogel composite sensing layers using chemical or biological membranes as hydrogel matrices. In this work, luminol is electropolymerized under near-neutral conditions onto screen-printed electrode (SPE)-supported hydrogel films. The working electrode coated with a hydrogel film is soaked in a solution containing monomeric luminol units, allowing the monomeric luminol units to diffuse inside the porous matrix to the electrode surface where they are electropolymerized by cyclic voltammetry (CV). Sensors and enzymatic biosensors for H2O2 and choline detection, respectively, have been developed, using choline oxidase (ChOD) as a model enzyme. In this case, hydrogel is used both as the enzymatic immobilization matrix and as a template for the electrosynthesis of polyluminol. The enzyme was immobilized by entrapment in the gel matrix during its formation before electropolymerization of the monomer. Several parameters have been optimized in terms of polymerization conditions, enzyme loading, and average pore size. Using calcium alginate or tetramethoxysilane (TMOS)-based silica as porous matrix, H2O2 and choline detection are reported down to micromolar concentrations with three orders of magnitude wide dynamic ranges starting from 4 × 10−7 M. Polyluminol/hydrogel composites appear as suitable electrochemiluminescence (ECL)-active sensing layers for the design of new reagentless and disposable easy-to-use optical sensors and biosensors, using conventional TMOS-based silica gel or the more original and easier to handle calcium alginate, reported here for the first time in such a configuration, as the biocompatible hydrogel matrix.

Immobilization of enzymes on the transducer surface is a necessary and critical step in the design of biosensors. An overview of the different immobilization techniques reported in the literature is given, dealing with classical adsorption, covalent bonds, entrapment, cross-linking or affinity as well as combination of them and focusing on new original methods as well as the recent introduction of promising nanomaterials such as conducting polymer nanowires, carbon nanotubes or nanoparticles. As indicated in this review, various immobilization methods have been used to develop optical, electrochemical or gravimetric enzymatic biosensors. The choice of the immobilization method is shown to represent an important parameter that affects biosensor performances, mainly in terms of sensitivity, selectivity and stability, by influencing enzyme orientation, loading, mobility, stability, structure and biological activity.

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-toperform, 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.

Advances in the development and the applications of optical biosensing systems based on immobilized aptamers are presented. These nucleic acid sequences have been used as new molecular recognition elements to develop heterogeneous assays, biosensors and microarrays. Among different detection modes that have been employed, optical ones which are described here are among the most used. Since their first report in 1996, numerous optical detection systems using aptamers and mainly based on fluorescence have been developed. Two main approaches have been used: label-based (using fluorophore, luminophore, enzyme, nanoparticles) or aptamer label-free detection systems (e.g. surface plasmon resonance, optical resonance). Most methods are based on a labeling approach. Some targets can be optically detected using not only colorimetry, chemiluminescence or the most developed fluorescence mode but also more recent non conventional optical methods such as surface plasmon-coupled directional emission (SPCDE). The first SPCDE-based aptasensor for thrombin detection has recently been reported in 2009. Aptasensors based on surface-enhanced Raman scattering spectroscopy (SERS) which presents advantages compared to fluorescence have also been described. Different label-free techniques have recently been shown to be suitable for developing performant aptasensors or aptamer-based microarrays, such as surface plasmon resonance (SPR), diffraction grating, evanescent-field-coupled (EFC) waveguide-mode, optical resonance or Brewster angle straddle interferometry (BASI). Important advances have been realized on optical aptamer-based detection systems that appear as highly efficient devices with enormous potential.

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.

In the nanotechnology field, the concept of using biomolecules as an elementary structure to develop self-assembled entities has received considerable attention. Particularly, the ability of amphiphilic molecules like lipids to self-organize into bilayers can be exploited to provide biomimetic membrane models. Langmuir–Blodgett (LB) technology, based on the transfer of an interfacial film onto a solid support, offers the possibility to prepare lipid bilayers suitable for biomolecule immobilization and achievement of nanoscale-organized sensing layers, tailored for the design of miniaturized biosensors. With the aim of immobilizing enzymes in a defined orientation at the surface of LB bilayers, an original strategy has been previously developed in our group. This approach combines two techniques based on molecular self-assembly properties: liposome fusion at an air/buffer interface and Langmuir–Blodgett technology. It allows the functional insertion of a non-inhibitory antibody in lipid bilayers, further used to anchor a soluble enzyme at the surface of the lipid membrane. When associated with an electrochemiluminescent (ECL) sensor, this molecular assembly allows the design of a biomimetic sensor able to closely integrate the recognition and transduction events. However, sensor's performance not only depends on bioactive sensing layer properties, but also on the additional introduction of luminol in the reaction medium which delays ECL reaction. This work explores the potentiality of two neosynthesized amphiphilic luminol derivatives to form a lipid bilayer serving as a matrix used for both antibody insertion and ECL detection in order to develop a new sensing layer allowing a reagentless detection. As a model, choline oxidase activity has been detected. After enzyme immobilization at the surface of the luminol derivative LB bilayer by the way of specific recognition of a non-inhibitory antibody, in situ catalytic generation of hydrogen peroxide is able to trigger ECL reaction in the sensing layer interfaced with an optoelectronic device leading to a reagentless detection of choline oxidase activity.

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.

Enzymes are very efficient biocatalysts, which have the ability to specifically recognize their substrates and to catalyze their transformation These unique properties make the enzymes powerful tools to develop analytical devices. Enzyme-based biosensors associate intimately a biocatalyst-containing Sensing layer with a transducer. The transformations catalyzed by an enzyme come with the variations of some physicochemical parameters The role of the transducer is to convert those physicochemical signals into a measureble electrical signal. In biosensors, enzymes are generally immobilized oil or close to the transducer. Depending oil the chemical and physical characteristics of the enzyme support, different immobilization techniques can be implemented The transduction mode will be adapted to the physicochemical parameter that is monitored. The variation of the concentration Of :I Substrate or a product in the course of all enzymatic reaction earl be detected with the help of a physical or chemical sensor, which then acts as a transducer Electrochemical biosensors have been then developed involving oxidoreduction reactions. Optical biosensors are based either on fluorescence, absorbance, and bioluminescence Or chemiluminescence measurement Enzymatic reactions are usually associated with a high enthalpy change, which results in a temperature variation that can be recorded using a thermistor. Gravimetric biosensors are based oil a mass variation induced by an enzymatic reactionDue to their proteic nature, enzymes are often fragile and this instability results in a decrease in the enzyme activity and consequently in a decrease in the biosensor performances. Although, fortunately, not all enzymes are concerned, this call unlit the development of enzyme-based biosensors. The first biosensors described were the size of a pH electrode but now the progress in the transducer technology makes the fabrication of miniaturized systems possible and this allows the development of small-sized multi-biosensors and the integration of miniaturized biosensors in lab-on-a-chip-type devices.

This paper describes two configurations that integrate electrochemical detection into microfluidic devices. The first configuration is a low-cost approach based on the use of PCB technology. This device was applied to electrochemiluminescence detection. The second configuration was used to carry out amperometric quantification of electroactive species using a serial dilution microfluidic system.

This review presents electrochemical aptasensors reported in the literature. Their development has been growing as evidenced by the increasing number of scientific publications on this subject since 2004. Aptasensors are presented according to their transduction mode, including the most described amperometric and impedimetric devices as well as FETs and the first very recently reported potentiometric aptasensor. 'Signal-on' (positive readout signal) Mid less sensitive 'signal-off' (negative readout signal) aptasensors are reviewed based oil target hinding-induced conformational change of aptamers or on target binding-induced strand displacement or even oil both processes. Aptamer-labeled and aptamer label-free devices are presented separately.

In this work chemiluminescence (CL) of luminol was used for the determination of Co(II). This method is based on the fact that Co(II) catalyzes the CL reaction of luminol in the presence of H2O2. The optimization of the conditions of CL measurements in a liquid system (effect of luminol and H2O2 concentrations) is studied. This method has shown a remarkable sensitivity until 4 fg/L of Co(II) as detection limit. The linear range extends from 0.4 pg/L to 40 mu g/L of Co(II). The optimum conditions for the preparation of the chitosan membranes for the adsorption of cobalt ions were studied. The analytical characteristics of the membrane/liquid CL system are similar to those of the CL liquid system. The preconcentration of cobalt ions on the chitosan membrane presented here opens up possibilities for a number of biomedical applications for determination of Vitamin B-12 containing a cobalt ion in pharmaceuticals, human serum, egg yolk and fish tissue, and for environmental applications for the detection of cobalt in soils and river waters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

This paper presents the design of two configurations of electrodes ("gold versus Ag/AgCl" and "gold versus gold") and an electrochemiluminescence (ECL) microfluidic device fabricated in the inexpensive printed circuit board (PCB) technology. The PCB electrodes are electrochemically characterized to determine appropriate working potentials. The ECL microfluidic device with integrated PCB electrodes is tested using luminol as luminophore to quantify H2O2 concentrations. Synchronous detection technique is implemented for weak signal recovery. For both PCB electrode configurations, a 100 nM H2O2 concentration is detected and a linear range extending from 1.00 nM to 10 mM is observed with a photomultiplier tube. A lab-on-board compatible potentiostat and a compact CMOS photodetector module are also designed and validated. The proposed instrumental approach may represent a low-cost way to develop portable analytical systems.

Amphiphilic luminol derivatives have been evaluated for electrochemiluminescence (ECL) measurements with a view to develop new lipid membranes as sensing element of nanobiosensors. The design and synthesis of new biospecific luminol derivatives with various substitution groups have been then undertaken. In a first approach, the possibility to use polarized screen-printed electrodes to trigger ECL in a buffer solution containing luminol derivatives and hydrogen peroxide has been studied. The ECL response to H2O2 in the presence of these luminescent derivatives has been investigated taking into account crucial factors such as the applied potential value, concentration of luminol derivatives and the substitution group in molecular structures. The lower hydrogen peroxide concentration detected varied from 1×10−7M to 5×10−5M, depending on the substitution group in the luminol derivative structures.

This paper presents an inexpensive approach of implementing electrochemiluminescence (ECL) detection for microfluidic analytical systems. It consists in using printed circuit board (PCB) technology to design electrodes and sealing the epoxy substrate with a transparent microfluidic structure in polymer for ECL detection and system integration. A pair of PCB electrodes (10 mm(2)) and an ECL microfluidic device are designed and fabricated. They are tested via luminol ECL detection to quantify H2O2. Characterization of the PCB electrodes is performed via the determination of the optimum potential (0.7 V vs. Ag/AgCl) to trigger luminol oxidation. Electrode potential is square-wave modulated from 0 to 0.7 V at a minimum period of 17 s. Measurements of on/off modulated ECL signals for different H2O2 concentrations are carried out to establish their relationship. The obtained results show a 50-nM detection limit at a signal-to-noise ratio (SNR) equal to 3 and a linear range extending up to 0.1 mM in batch or in microfluidic conditions. The detection volumes for these two systems are 2 ml and 4 mu l, respectively. (c) 2007 Elsevier B.V. All rights reserved.