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Growth arrest-specific 6 (GAS6) protein plays a key role in processes related to proliferation, inflammation, angiogenesis, and atherosclerotic plaque formation. In addition, it has been reported that plasma levels of GAS6 are related to cancer prognosis and other relevant pathologies, such as heart failure or sepsis. We report here the first electrochemical immunoplatform for the determination of GAS6, which has demonstrated to be competitive with other available methodologies in terms of cost, simplicity, and decentralized application. The developed immunoplatform involves a sandwich immunoassay using magnetic microparticles (MBs) and uses amperometric detection at disposable screen-printed carbon electrodes (SPCEs). The MBs were modified with an antibody specific to GAS6 for its selective capture, which is further recognized by a biotinylated secondary antibody subsequently labeled with a streptavidin-horseradish peroxidase (Strep-HRP) conjugate. The electrochemical detection was carried out using the hydroquinone (HQ)/H2O2 system. The developed bioplatform exhibits a great selectivity and low limit of detection (27 pg/mL) that allowed the determination of the GAS6 circulating level in plasma samples from patients suffering heart failure (HF) and diagnosed with pancreatic ductal adenocarcinoma (PDAC), as well as the determination of the target protein in raw secretomes of human colorectal cancer cell lines., This work is part of the POSITION-II project fundedby the ECSEL Joint Undertaking under grant numberEcsel-783132-Position-II-2017-IA;www.position-2.eu,and PCI2018-093067 (Spanish Ministerio de Ciencia eInnovación) to M.P. The financial support of PID2019-103899RB-I00 (Spanish Ministerio de Ciencia e Inno-vación) Research Project to S.C., PI17CIII/00045 andPI20CIII/00019 grants from the AES-ISCIII program toR.B. and the TRANSNANOAVANSENS-CM Program fromthe Comunidad de Madrid (Grant S2018/NMT-4349) toS.C., RTI2018-095672-B-I00 (Spanish Ministerio de Cienciae Innovación) to P.G.F.; Fundació la Marató de TV3 project081010toM.B.; researchprojectPI20/00625,fromtheAES-ISCIII/FEDER program, to P.N, are gratefully acknowl-edged. A. Montero-Calle acknowledges the support of theFPU predoctoral contracts by the Spanish Ministerio deEducación, Cultura y Deporte. G.S-F. is recipient of a pre-doctoral contract (grant number 1193818N) supported byThe Flanders Research Foundation (FWO). C. Muñoz-SanMartín acknowledges a predoctoral contract from Complutense University of Madrid. R.M. Torrente-Rodríguezacknowledges a Talento-Contract from Comunidad deMadrid (2019-T2/IND-15965).

Construction of artificial allosteric protein switches is one of the central goals of synthetic biology that holds promise to transform the way we detect and quantify substances in vitro and in vivo. An artificial chimeric fusion protein of pyrroloquinoline quinone-dependent glucose dehydrogenase with calmodulin (PQQ-GDH-CaM) was covalently attached to graphene nanosheets produced electrochemically on a carbon fiber electrode. The chimeric PQQ-GDH-CaM represents an artificial allosteric switch activated by association of a calmodulin-binding peptide with the Ca2+-bound calmodulin domain. The activity of the immobilized enzyme was switched between active and inactive states by adding/removing the activating peptide. The peptide-signal switchable features originated from the enzyme 3D-structural variations induced by the conformational (folding/unfolding) changes in the connected calmodulin unit upon formation/dissociation of its complex with the specific peptide. The peptide-activated immobilized PQQ-GDH-CaM enzyme displayed direct (non-mediated) electron transfer to the conducting electrode support upon glucose oxidation. On the contrary, in the absence of the peptide, the inactive form of the enzyme demonstrated very low bioelectrocatalytic activity for glucose oxidation. Since the conformational changes of the PQQ-GDH-CaM depend on the presence of Ca2+ cations and the calmodulin-binding peptide, both of them were used as input signals to control the enzyme activity mimicking a Boolean AND logic gate. The switchable behavior of the enzyme-modified electrode was studied electrochemically and used to assemble a signal-switchable biofuel cell. The use of the peptide as the signaling messenger enables the design of generalizable bioelectronic systems controlled by native and synthetic biochemical signaling systems.

Electrodes composed of carbon fibers were modified with graphene nano-sheets in order to increase their surface area and facilitate electrochemical reactions. Electrocatalytic species, such as Meldola's blue (MB) and hemin were immobilized on the graphene surface due to their π-π stacking and then used for electrocatalytic oxidation of NADH and reduction of H2O2, respectively. Further modification of these electrodes with enzymes producing NADH and H2O2 in situ (lactate dehydrogenase, LDH, and lactate oxidase, LOx, respectively), allowed assembling of a biofuel cell operating in the presence of lactate, oxygen and NAD+. The cathode of the biofuel cell required lactate and O2 for its operation, while the anode operated in the presence of lactate and NAD+. Notably, both bioelectrocatalytic electrodes operated in the presence of lactate, one producing H2O2 in the reaction catalyzed by LOx in the presence of O2, second producing NADH in the reaction catalyzed by LDH in the presence of NAD+. Both reactions were performed in the biofuel cell without separation of the cathodic and anodic solutions and with no need of a membrane. The biofuel cell was tested in solutions mimicking human sweat and then in real human sweat samples, demonstrating substantial power release being able to activate electronic devices.

A graphene-functionalized carbon fiber electrode was modified with adsorbed polyethylenimine to introduce amino functionalities and then with trigonelline and 4-carboxyphenylboronic acid covalently bound to the amino groups. The trigonelline species containing quarterized pyridine groups produced positive charge on the electrode surface regardless of the pH value, while the phenylboronic acid species were neutral below pH 8 and negatively charged above pH 9 (note that their pKa=8.4). The total charge on the monolayer-modified electrode was positive at the neutral pH and negative at pH > 9. Note that 4-carboxyphenylboronic acid was attached to the electrode surface in molar excess to trigonelline, thus allowing the negative charge to dominate on the electrode surface at basic pH. Negatively charged fluorescent dye-labeled insulin (insulin-FITC) was loaded on the modified electrode surface at pH 7.0 due to its electrostatic attraction to the positively charged interface. The local pH in close vicinity to the electrode surface was increased to ca. 9–10 due to consumption of H+ ions upon electrochemical reduction of oxygen proceeding at the potential of −1.0 V (vs. Ag/AgCl) applied on the modified electrode. The process resulted in recharging of the electrode surface to the negative value due to the formation of the negative charge on the phenylboronic acid groups, thus resulting in the electrostatic repulsion of insulin-FITC and stimulating its release from the electrode surface. The insulin release was characterized by fluorescence spectroscopy (using the FITC-labeled insulin), by electrochemical measurements on an iridium oxide, IrOx, electrode and by mass spectrometry. The graphene-functionalized carbon fiber electrode demonstrated significant advantages in the signal-stimulated insulin release comparing with the carbon fiber electrode without the graphene species.

Single-stranded DNA molecules were loaded on the mixed poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA)/poly(methacrylic acid) (PMAA) brush covalently attached to an indium tin oxide (ITO) electrode on a flexible support. The DNA deposition was performed at pH 5.0 when the polymer brush is positively charged due to protonation of tertiary amino groups in PDMAEMA, thus resulting in electrostatic attraction of the negatively charged DNA. By applying electrolysis at −1.0 V (vs. Ag/AgCl reference) electrochemical oxygen reduction resulted in the consumption of hydrogen ions and local pH increase in the vicinity of the electrode surface. The process resulted in the transition to negative charge of the mixed polymer-brush due to dissociation of carboxylic groups of PMAA. This resulted in the electrostatic repulsion and release of the loaded DNA. The developed approach allows cyclic load-release of the DNA with the significantly increased amount of the released DNA comparing with previously reported systems. Further options for the improvements of the system are discussed.

A new bioelectronic system activated by a DNA-signal and releasing another DNA has been designed. The system was composed of two modified electrodes: one electrode functionalized with enzymes was activated with a DNA-signal, while another electrode coated with an alginate film released pre-loaded DNA species, when the first electrode was activated. The sensing electrode was functionalized with pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) producing negative potential in the presence of glucose. This bioelectrocatalytic process was inhibited by the presence of glucose oxidase (GOx) at the external surface of the biomolecular system organized on the electrode surface through a DNA-linker. GOx consumed incoming glucose and did not allow its penetration to the internal layer functionalized with PQQ-GDH, thus leaving the electrode mute. The DNA-signal resulted in the detachment of GOx and activated the process biocatalyzed by PQQ-GDH due to penetration of glucose to the internal layer at the electrode surface. Finally, formation of a negative potential on the sensing electrode resulted in the activation of the second electrode and DNA release from the alginate matrix. The Sense-and-Act system allowed amplification of the DNA-signal by releasing much higher amount of DNA comparing with the applied DNA-signal. The DNA-signal amplification will find applications in various biosensor and biomolecular computing systems.

Graphene nanosheets were produced on the surface of carbon fibers by in situ electrochemical procedure including oxidative and reductive steps to yield first graphene oxide, later converted to graphene. The electrode material composed of graphene-functionalized carbon fibers was characterized by scanning electron microscopy (SEM) and cyclic voltammery demonstrating superior electrochemical kinetics comparing with the original carbon paper. The interfacial electron transfer rate for the reversible redox process of [Fe(CN)6]3−/4− was found ca. 4.5-fold higher after the electrode modification with the graphene nanosheets. The novel electrode material is suggested as a promising conducting interface for bioelectrocatalytic electrodes used in various electrochemical biosensors and biofuel cells, particularly operating in vivo.

Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor involved in tumor growth and metastasis by regulating genes involved in response to hypoxia. This work reports the first magnetic beads (MBs)-based electrochemical immunoassay for the determination of HIF-1α. The design involves a sandwich immunoassay using MBs and amperometric detection at disposable screen-printed carbon electrodes (SPCEs). Magnetic immunoconjugates of carboxylic acid-microsized magnetic particles (HOOC-MBs) modified with a specific antibody were used to selectively capture the target protein which was sandwiched with a biotinylated secondary antibody further conjugated with a streptavidin peroxidase conjugate (Strep-HRP). The great analytical performance of the immunoassay in terms of selectivity and low limit of detection (76 pg mL−1) for HIF-1α allows the determination of the endogenous amount of this biomarker in 0.5 μg raw cancer cells lysates cultured in normoxia or induced-hypoxia with CoCl2. In addition, the developed immunosensing approach was employed to analyze HIF-1α in saliva samples with results that agree with those provided by an ELISA kit involving the same immunoreagents.

Single-stranded DNA molecules were loaded on the mixed poly(2-vinylpyridine) (P2VP)/polyacrylic acid (PAA) brush covalently attached to an indium tin oxide (ITO) electrode. The DNA deposition was performed at pH 3.0 when the polymer brush is positively charged due to protonation of pyridine groups in P2VP, thus resulting in electrostatic binding of the negatively charged DNA. By applying electrolysis at −1.0 V (vs. Ag/AgCl reference) oxygen reduction resulted in the consumption of hydrogen ions and local pH increase in the vicinity of the electrode surface. The process resulted in the local pH ca. 7.5 which yielded the negative state of the mixed polymer-brush due to dissociation of carboxylic groups of PAA. This resulted in the electrostatic repulsion and release of the loaded DNA. The developed approach allows cyclic load-release of the DNA with the significantly increased amount of the released DNA comparing with previously reported systems. Further options for the improvements of the system are discussed.

A bioelectronic system composed of two modified electrodes, one activated in the presence of ketone bodies, a biomarker of diabetic ketoacidosis, and another releasing insulin upon receiving a signal, was designed and tested in vitro to operate as a Sense-and-Act device. The functional integration of biomarker-sensing and insulin-releasing electrodes represents a step to a theranostic system with autonomous operation.

Signal-controlled release of DNA from Fe

A modified electrode with bioaffinity to E. coli bacterial cells was used to detect bacteria presence on its surface and to produce an electrical signal triggering antibacterial drug release from another coupled electrode. The Sense-and-Treat system was realized in two different versions and suggested as the first step to future theranostic applications where bacteria presence results in automatic antibacterial treatment.

A novel hybrid nanomaterial was synthesised by covalent attachment of O-carboxymethylcellulose to reduced graphene oxide. Graphene oxide was first anchored with (3-aminopropyl)triethoxysilane moieties to provide reactive primary amino groups at the basal plane. Periodate-oxidised O-carboxymethylcellulose was further covalently attached to this aminated nanomaterial through reductive alkylation with NaBH4. Stable aqueous dispersions were obtained with the resulting hybrid nanomaterial, which was used to coat glassy carbon electrodes. Furthermore, the enzyme tyrosinase was covalently immobilised and the nanostructured enzyme electrode was successfully employed for the amperometric detection of catechol in the 20 nM–56 μM range. The biosensor showed excellent analytical performance with a high sensitivity of 270 mA M−1 and a low detection limit of 0.2 nM.

Disposable amperometric magnetosensors, involving a mixture of modified-magnetic beads (MBs), for the multiplex screening of cephalosporins (CPHs), sulfonamides (SAs) and tetracyclines (TCs) antibiotic residues in milk are reported for the first time in this work. The multiplexed detection relies on the use of a mixture of target specific modified magnetic beads (MBs) and application of direct competitive assays using horseradish peroxidase (HRP)-labeled tracers. The amperometric responses measured at −0.20 V vs . the Ag pseudo-reference electrode of screen-printed carbon electrodes (SPCE) upon the addition of H 2 O 2 in the presence of hydroquinone (HQ) as redox mediator, were used to monitor the extent of the different affinity reactions. The developed methodology, involving a simple and short pretreatment, allowed discrimination between no contaminated UHT and raw milk samples and samples containing antibiotic residues at the maximum residue limits (MRLs). The usefulness of the multiplexed magnetosensor was demonstrated by analyzing spiked milk samples in only 5 min. The results demonstrated that a clear discrimination of milk samples contaminated with antibiotics at their MRL level or their mixtures, allowing the identification of milk not complying with current legislation. These features make the developed methodology a promising alternative in the development of user-friendly devices for on-site analysis to ensure quality control for dairy products.

In the last fifteen years, the nucleic acid biosensors and delivery area has seen a breakthrough due to the interrelation between the recognition of nucleic acid’s high specificity, the great sensitivity of electrochemical and optical transduction and the unprecedented opportunities imparted by nanotechnology. Advances in this area have demonstrated that the assembly of nanoscaled materials allows the performance enhancement, particularly in terms of sensitivity and response time, of functional nucleic acids’ biosensing and delivery to a level suitable for the construction of point-of-care diagnostic tools. Consequently, this has propelled detection methods using nanomaterials to the vanguard of the biosensing and delivery research fields. This review overviews the striking advancement in functional nanomaterials’ assisted biosensing and delivery of nucleic acids. We highlight the advantages demonstrated by selected well-known and rising star functional nanomaterials (metallic, magnetic and Janus nanomaterials) focusing on the literature produced in the past five years.

A non-invasive, passive and simple to use skin surface based sensing device for determining the blood's ethanol content (BAC) by monitoring transdermal alcohol concentration (TAC) is designed and developed. The proposed prototype is based on bienzyme amperometric composite biosensors that are sensitive to the variation of ethanol concentration. The prototype correlates, through previous calibration set-up, the amperometric signal generated from ethanol in sweat with its content in blood in a short period of time. The characteristics of this sensor device permit determination of the ethanol concentration in isolated and in continuous form, giving information of the BAC of a subject either in a given moment or its evolution during long periods of time (8h). Moreover, as the measurements are performed in a biological fluid, the evaluated individual is not able to alter the result of the analysis. The maximum limit of ethanol in blood allowed by legislation is included within the linear range of the device (0.0005-0.6 g L(-1)). Moreover, the device shows higher sensitivity than the breathalyzers marketed at the moment, allowing the monitoring of the ethanol content in blood to be obtained just 5 min after ingestion of the alcoholic drink. The comparison of the obtained results using the proposed device in the analysis of 40 volunteers with those provided by the gas chromatographic reference method for determination of BAC pointed out that there were no significant differences between both methods.

The design, preparation and analytical performance of a novel integrated amperometric immunosensor based on the immobilization of selective capture antibodies on the surface of Protein G-modified screen-printed dual carbon electrodes (SPdCEs) for the multiplexed determination of sulfonamide and tetracycline antibiotics residues in milk is reported in this work. Protein G was covalently immobilized onto a 4-aminobenzoic acid (4-ABA) film grafted on the disposable electrode, and a direct competitive immunoassay using horseradish peroxidase (HRP)-labeled tracers was performed. The amperometric responses measured at -0.2 V vs. the silver pseudo-reference electrode of the SPdCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as mediator were used to monitor the extent of the immunoreactions. The developed methodology showed very low limits of detection (in the low ppb level) for sulfonamide and tetracycline antibiotics tested in untreated milk samples, and a good selectivity against other antibiotic residues frequently detected in milk and dairy products. The usefulness of the dual immunosensor was demonstrated by analyzing spiked milk samples as well as a reference milk containing a certified oxytetracycline (OTC) content. Good recoveries were attained in an analysis time of 30 min.

Novel label free electrochemical magnetoimmunosensors for the determination of lactoperoxidase (LPO) were developed based on the use of streptavidin-magnetic beads (Strep-MBs) and graphite-Teflon composite or screen-printed carbon electrodes (SPCEs) as electrochemical transducers. Biotinylated antiLPO antibodies were immobilized onto the Strep-MBs and a direct-type immunoassay by detecting the enzymatic activity of the captured target enzyme using amperometric detection at −0.20 V and the H2O2/hydroquinone (HQ) system was employed. The SPCEs-based magnetoimmunosensors allowed a detection limit (LOD) of 0.12 μg mL−1 and a good selectivity against nontarget proteins. Moreover, their analytical usefulness was successfully demonstrated by analyzing different types of milk samples.

We study the mechanisms involved in the release, triggered by the application of glucose, of insulin entrapped in Fe

Two different D-dimer disposable amperometric immunosensing designs based on indirect competitive or sandwich formats and the use of carboxylic acid-modified magnetic beads (COOH-MBs) and screen-printed carbon electrodes (SPCEs) have been developed and compared. In both approaches, the resulting modified MBs were magnetically captured on the surface of a SPCE which was used as the transducer for the electrochemical detection at −0.20 V upon addition of H2O2, and hydroquinone (HQ). Both configurations exhibited linear ranges of clinical usefulness and detection limits quite below the clinical threshold (0.5 µg mL−1 D-dimer). The sandwich configuration has been successfully tested with serum samples.

The preparation and performance of a disposable amperometric magneto-immunosensor, involving the use of a selective capture antibody immobilized on the surface of protein G-functionalized magnetic beads (ProtG-MBs) and screen-printed carbon electrodes (SPCEs), for the specific detection and quantification of tetracyclines (TCs) residues in milk is reported. A direct competitive immunoassay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling was performed. The amperometric response measured at -0.2 V vs. the silver pseudo-reference electrode of the SPCE upon the addition of H(2)O(2) in the presence of hydroquinone (HQ) as redox mediator was used as transduction signal. The developed methodology showed very low limits of detection (in the low ppb level) for 4 tetracycline antibiotics tested in untreated milk samples, and a good selectivity against other antibiotic residues frequently detected in milk and dairy products. The usefulness of the magneto-immunosensor was demonstrated by analyzing UHT whole milk samples spiked with 44 ng mL(-1) tetracycline (TC) as well as a reference milk containing a certified oxytetracycline (OTC) content. These features, together with the short analysis time (30 min), the simplicity, and easy automation and miniaturization of the required instrumentation make the developed methodology a promising alternative in the development of devices for on-site analysis.

A new layer-by-layer supramolecular approach for the construction of self-assembled nanoarchitectures of polyamidoamine (PAMAM) dendrimers and peroxidase on gold surface is reported. The methodology is based on the supramolecular self-assembly of alternated layers of adamantane-modified horseradish peroxidase and β-cyclodextrin-branched PAMAM G-5 dendrimers on a gold electrode, previously coated with β-cyclodextrin-modified cysteamine core PAMAM G-4 dendron. The formation of layer-by-layer assemblies (up to three dendrimer/peroxidase bilayers) was studied by SPR, quartz crystal microbalance, AFM and cyclic voltammetry. The analytical applicability of these architectures was evaluated by constructing a H 2 O 2 biosensor. The electroanalytical response of the biosensor towards H 2 O 2 increased with the number of enzyme layers. The bioelectrode constructed with three enzyme layers showed a low detection limit of 160 nM, a sensitivity of 602 μA/M cm 2 and retained 63% of its initial activity after 30 days of storage in wet conditions.

The preparation and performance of a disposable amperometric immunosensor, based on the use of a selective capture antibody and screen-printed carbon electrodes (SPCEs), for the specific detection and quantification of sulfonamide residues in milk is reported. The antibody was covalently immobilized onto a 4-aminobenzoic acid (4-ABA) film grafted on the disposable electrode, and a direct competitive immunoassay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling was performed. The amperometric response measured at −0.2 V vs the silver pseudo-reference electrode of the SPCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as mediator was used as transduction signal. The developed methodology showed very low limits of detection (in the low ppb level) for 6 sulfonamide antibiotics tested in untreated milk samples, and a good selectivity against other families of antibiotics residues frequently detected in milk and dairy products. These features, together with the short analysis time (30 min), the simplicity, and easy automation and miniaturization of the required instrumentation make the developed methodology a promising alternative in the development of devices for on-site analysis.

Integrated amperometric biosensors for the determination of l-malic and l-lactic acids were developed by coimmobilization of the enzymes l-malate dehydrogenase (MDH) and diaphorase (DP), or l-lactate oxidase (LOX) and horseradish peroxidase (HRP), respectively, together with the redox mediator tetrathiafulvalene (TTF), on a 3-mercaptopropionic acid (MPA) self-assembled monolayer (SAM)-modified gold electrode by using a dialysis membrane. The electrochemical oxidation of TTF at +100 mV (vs. Ag/AgCl), and the reduction of TTF+ at -50 mV were used for the monitoring of the enzyme reactions involved in l-malic and l-lactic acid determinations, respectively. Experimental variables concerning the biosensors composition and the detection conditions were optimized for each biosensor. Good relative standard deviation values were obtained in both cases for the measurements carried out with the same biosensor, with no need of cleaning or pretreatment of the bioelectrodes surface, and with different biosensors constructed in the same manner. After 7 days of continuous use, the MDH/DP biosensor still exhibited 90% of the original sensitivity, while the LOX/HRP biosensor yielded a 91% of the original response after 5 days. Calibration graphs for l-malic and l-lactic were obtained with linear ranges of 5.2 × 10-7 to 2.0 × 10-5 and 4.2 × 10-7 to 2.0 × 10-5 M, respectively. The calculated detection limits were 5.2 × 10-7 and 4.2 × 10-7 M, respectively. The biosensors exhibited a high selectivity with no significant interferences. They were applied to monitor malolactic fermentation (MLF) induced by inoculation of Lactobacillus plantarum CECT 748T into a synthetic wine. Samples collected during MLF were assayed for l-malic and l-lactic acids, and the results obtained with the biosensors exhibited a very good correlation when plotted against those obtained by using commercial enzymatic kits. © 2010 Elsevier B.V. All rights reserved., The financial support of the Spanish Ministerio de Educación y Ciencia Research Project CTQ2006-02743BQU

The use of lectins for microorganism biosensors fabrication is proposed. Lectins are immobilised onto a gold-plated quartz crystal for direct piezoelectric label-free transduction of the bacteria-lectin binding event using an electrochemical quartz crystal microbalance (EQCM). Concanavalin A (Con A) and Escherichia coli were used for the evaluation of the lectin immobilisation method and the biosensor performance. Adsorption on nonpolarised and polarised (-0.200 V) gold-coated quartz crystals and immobilisation through avidin-biotin binding were checked for Con A surface attachment. Lectin-bacteria binding was evaluated in all cases. With a crystal modified with Con A via avidin-biotin immobilisation we obtained a linear calibration plot between 5.0 x 10(6) and 2.0 x 10(7) cfu mL(-1) by measuring frequency changes with E. coli concentration 1 h after bacteria addition. A remarkable increase in sensitivity was achieved when the analytical solution contained free biotinylated Con A, as a consequence of multiple lectin adhesion to Escherichia coli cell wall, which produced an accumulation of Con A-E. coli conjugates in the form of multilayers at the electrode surface. A detection limit of approximately 1.0 x 10(4) cfu mL(-1) was achieved. Moreover nonspecific adsorptions were minimised. Using Con A and lectin from Arachis hypogaea, different response profiles were achieved for Escherichia coli, Staphylococcus aureus and Mycobacterium phlei, thus demonstrating the feasibility of bacteria discrimination. An approach involving filtering of free and lectin-bound bacteria and introduction of a filter in the measuring cell allowed a significant frequency change to be obtained for an E. coli concentration of 1.0 x 10(3) cfu mL(-1) in order to further increase the sensitivity and discriminate between viable and nonviable cells; an approach using electrochemical measurements of bacterial catalase activity was also checked.