Screen Printed Electrode

According to the World Health Organisation, worldwide waterborne diseases are responsible for nearly two million human deaths annually. Rapid and at-site screen of pathogenic microorganisms in drinking water can help to markedly reduce this number. Here we report an innovative, simple and low-cost, paper-based probe for detection of bacteria in water, fabricated by screen printing carbon electrodes onto hydrophobic paper. Electrochemical characterization of the printed electrodes confirmed fast-electron transfer, with an estimated electroactive surface area of 0.25 cm 2 . The electrode surface was functionalised with carboxyl groups, prior to covalent immobilisation of the lectin concanavalin A (Con A), used as the biorecognition element. The system was then tested as an impedimetric sensor for bacteria in water. A linear increase in the probe charge transfer resistance was observed for bacterial concentrations ranging from 10 3 to 10 6 CFU mL -1 , with an estimated lower detection limit of 1.9 × 10 3 CFU mL -1 . Considering its remarkable simplicity, cost-effectiveness and biodegradability, the sensor here reported could be an attractive solution for portable testing kits that address the challenges of traditional timeconsuming and expensive lab-based analyses.

This work reports the development of an amperometric glucose-6-phosphate biosensor by coimmobilizing p-hydroxybenzoate hydroxylase (HBH) and glucose-6-phosphate dehydrogenase (G6PDH) on a screen-printed electrode. The principle of the determination scheme is as follows: G6PDH catalyzes the specific dehydrogenation of glucose-6-phosphate by consuming NADP + . The product, NADPH, initiates the irreversible the hydroxylation of p-hydroxybenzoate by HBH in the presence of oxygen to produce 3, 4-dihydroxybenzoate, which results in a detectable signal due to its oxidation at the working electrode. The sensor shows a broad linear detection range between 2 µM and 1000 µM with a low detection limit of 1.2 µM. Also, it has a fast measuring time which can achieve 95% of the maximum current response in 20 s after the addition of a given concentration of glucose-6-phosphate with a short recovery time (2 min).

An innovative voltammetric sensor was developed to estimate omarigliptin, a novel long-acting anti-diabetic drug. The sensor utilized a carbon paste electrode enhanced with a nanocomposite of carbon nanotubes and electrodeposited gold nanoparticles. The modified electrode was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The modification significantly improved the electrode's sensitivity and electrochemical efficiency and decreased its electron transfer resistance. The surface area of the modified electrode increased by about 2.8-fold compared to the bare electrode. Omarigliptin's oxidation behavior on the modified electrode was pH-dependent and irreversible, resulting in a peak current 4 times higher than the unmodified electrode. The modified electrode revealed good reproducibility, reusability, and stability. It allows for sensitive voltammetric analysis of omarigliptin over a linear range of 0.4-27 μM (LOD = 0.12 μM) and good applicability in tablets and plasma. The recovery percentages were 98.47%-101.27% in tablets and 95.86%-105.02% in plasma. The modified electrode exhibits good selectivity towards omarigliptin without interference from tablet excipients, endogenous plasma components, and coadministered drugs. The comparison with the reported methods reveals the superiority of the proposed method in terms of sensitivity, selectivity, applicability, and eco-friendliness. Finally, the proposed method demonstrates excellent environmental profiles based on recent assessment metrics.

We present a methodology for the determination of gaseous elemental mercury (GEM). It is based on passive sampling of Hg on screen-printed gold electrodes (SPGEs), followed by the measurement of amalgamated mercury by square wave anodic stripping voltammetry. We have explored in detail the behavior of the SPGE electrode surface during the sampling process (by timeof-flight secondary ion mass spectrometry), the stability of the voltammetric signals, and the inter-electrode reproducibility, and obtained acceptable results. Adsorption of mercury onto the SPGE follows a nearly linear behavior until the sorbent becomes saturated (equilibrium phase) for different mercury concentrations, allowing to select a sampling time of 30 min for calibration. The theoretical behavior of the sampling system was modeled, considering the changes in the diffusive path length between the porous diffusive barrier and the adsorbed surface, L. Finally, we have tested two GEM calibration protocols. The first one is based on the measurement of the mercury stripping peak area, A Hg , and the second one is based on the measurement of the mass of mercury, m Hg , by standard additions. We found good correlation coefficients between the GEM concentration for both A Hg (R 2 = 0.9591) and m Hg (R 2 = 9615) in the range of 5.82 to 59.29 ng dm -3 GEM. Detection limits were 5.32 and 5.22 ng dm -3 for A Hg and m Hg , respectively. Our results open a new line of electroanalytical strategies for the determination of GEM in atmospheric samples.

This work describes the development of an electrochemical, recombinant Fab fragment-based immunosensor for the detection of testosterone in bovine urine. The sensor comprised of a testosterone conjugate on the surface of screen-printed electrodes, and recognition followed by an anti-testosterone Fab fragment. The use of an IgG-horseradish peroxidase conjugate determined the degree of competition. Chronoamperometry at a potential of +100 mV, was chosen to reductively measure the product of the catalysis of 3,3 ,5,5 -tetramethylbenzidine catalysis. ELISA was primarily used to investigate the assay system, prior to transferring to SPEs. The final Fab-based sensor exhibited the linear range of 300-40,000 pg/ml with limit of detection of 90 ± 13 pg/ml. Furthermore, the developed Fab sensor allowed for the determination of testosterone in bovine urine directly after dilution, omitting the necessity of extraction and hydrolysis. Comparison of administrated bovine urine samples between the developed Fab sensor and GC-MS data showed quantitative or semi-quantitative results and enabled identification of suspicious samples for further extensive analysis by established analytical techniques. With simple sample preparation, low limit of detection, and good repeatability, the proposed method can offer alternative advantages as a primary screening tool for meat quality control.

In the presented work, a disposable immunosensor for the detection of testosterone, an endogenous steroid hormone, in bovine urine has been developed using screen-printed electrodes (SPEs). Due to concerns over the use of steroid hormones as growth promoters, the EU prohibits their use in food producing animals. Consequently, rigorous screening procedures have been implemented in all member states to detect the illegal administration of such compounds. Competitive immunoassays were developed, initially by enzyme linked immunosorbent assay (ELISA), and subsequently transferred to an electrochemical immunosensor format using disposable screen-printed carbon electrodes. Horseradish peroxidase (HRP) was the enzyme label of choice and chronoamperometric detection was carried out using a tetramethylbenzidine/hydrogen peroxide (TMB/H 2 O 2 ) substrate system, at +100 mV. The EC 50 values obtained for the assay in buffer and urine gave relatively comparable results, 710 pg mL -1 and 960 pg mL -1 , respectively. The linear range obtained for the assay in buffer extended from 0.03 ng mL -1 to 40 ng mL -1 ; while that in urine ranged from 0.03 ng mL -1 to 1.6 ng mL -1 . The corresponding limits of detection (LOD) in buffer and urine were 26 pg mL -1 and 1.8 pg mL -1 . Cross reactivity profiles of the antibody have been examined, with notable cross reactivities with 19-nortestosterone (11.6%) and boldenone (9.86%). Precision studies for the sensor demonstrated adequate reproducibility (CV < 13%, n = 3) and repeatability (CV < 9%, n = 3). Recovery data obtained showed good agreement between spiking studies and known concentrations of analyte. Sensors showed stability for 4 days at +4 • C. A sensitive, highly specific, inexpensive, disposable immunosensor, showing excellent overall performance for the detection of testosterone in bovine urine, has been developed.

Foi realizado um estudo comparativo entre duas metodologias de imobilização do Azul de Meldola (MB), utilizado para diminuir o potencial de oxidação do NADH. O estudo foi realizado no eletrodo de carbono vítreo através da eletropolimerização do pirrol e MB, empregando a técnica de voltametria cíclica e avaliando-se o efeito do número de ciclos para definir a espessura e a estabilidade do filme. Com 25 ciclos foi obtido o melhor resultado. Foi também investigada a modificação do eletrodo de grafite com filme formado pelo sistema sol-gel PPO 300 ou PPO 4000 pelo método de recobrimento por mergulho, através de dois métodos: oclusão e adsorção. O melhor método foi o de adsorção da MB durante 10 min, seguida de depósito do filme PPO 300, favorecido pelo tempo de secagem (24 horas). A adsorção da MB seguido do depósito do PPO 300 apresentou maior intervalo linear do que a metodologia do PPY. A comparative study was accomplished between two immobilization methodologies for the meldola's blue (MB), used to decrease the oxidation potential of NADH. The study was performed with glassy carbon electrode by electropolymerization of pyrrole and MB through the technique of cyclic voltammetry being evaluated the effect of the number of cycles to define the thickness and the stability of the film. With 25 cycles it was obtained the best result. They were also investigated the modification of the graphite electrode with film formed by the system sol-gel PPO 300 or PPO 4000 for the dip-coating, through two methods: occlusion and adsorption. The best method was it of adsorption of MB during 10 min, following by deposit of the film PPO 300, favored for the time of drying (24 hours). The adsorption of MB followed by PPO 300 deposition presented broader linear range than PPy methodology

We report the first successful deposition of fibrinogen blood protein thin films by matrix assisted pulsed laser evaporation using a KrF * excimer laser. We have demonstrate by Fourier transform infrared spectroscopy (FTIR) that our thin films are composed of fibrinogen and fibrin maintaining their chemical structures. FTIR spectra, atomic force microscopy (AFM) micrographs and fibrinogen concentration depend on the laser fluence. The best results for fibrinogen deposition were obtained using lower fluences.

A disposable screen-printed multi channel taste sensor composed of several types of lipid as transducers and a computer as data analyzer could detect taste in a manner similar to human gustatory sensation. The disposable taste sensor was used to measure the electrical potential resulted from the interaction between lipid membranes and taste substances. In the present study, two types of packaged commercial milk, the ultra high temperature (UHT) and the pasteurized milk were tested. It was found that the disposable taste sensor is capable to discriminate reliably between fresh and spoiled milk and to follow the deterioration of the milk quality when it is stored at room temperature based on a pattern recognition principle namely Principle Component Analysis (PCA). This research could provide a new monitoring method ideally for simple and cheap decentralized testing for controlling the quality of milk, which may be of great use in the dairy industries.

In this study, a portable electronic tongue was developed and successfully used to distinguish and to discriminate quality of saffron samples. The proposed system consisted of an array of voltammetric sensors based on screenprinted electrodes (SPE), where the working electrodes were of different chemical natures (e.g. carbon, gold and modified carbon electrode). Moreover, the carbon electrodes were chemically modified by electrocatalytic copper phthalocyanine derivatives. The electrodes were immersed in saffron infusions to produce complex voltammetric curves that were characterised for each saffron sample. The electrochemical signals provided by the array showed good correlations with the data obtained from traditional chemical analysis, in particular with the kaempferol, a flavonol with antioxidant activity. The calibration model was optimised using more meaningful description of factors. Finally, discriminant analysis showed that the proposed e-tongue based on SPEs modified with phthalocyanine is useful for discrimination of saffron samples with different qualities. All of these results reveal that proposed e-tongue has a high potential for saffron quality control due to its very simple sample preparation and also its fast response.

A new approach for the electrochemical reduction of cytochromes P450 (P450, CYPs) with electrodes chemically modified with CYP appropriate substrates ("reverse" electrodes) has been proposed. The method is based on the analysis of cyclic voltammograms, square wave voltammograms, amperograms and determination of such electrochemical characteristics as catalytic current and redox potential. The differences of maximal current and potentials in square wave voltammograms and catalytic current in amperometric measurements are more sensitive and reliable. The planar mode of screen-printed electrodes permits to use 20-60 µ l of electrolyte volume. We have investigated P450 2B4-benzphetamine or P450scc-cholesterol enzyme-substrate pairs. Electrochemical parameters of electrodes with nonspecific P450 substrate were differed from the electrodes with appropriate substrates.

h i g h l i g h t s g r a p h i c a l a b s t r a c t A new probe has been developed for on-site analyses of free metal ion. A screen-printed electrode has been hyphenated to a DMT device. Analysis time has been reduced to 6H against 36H when using a classical DMT device. This new probe has been successfully applied on a synthetic freshwater sample.

The objective of this study was to exploit the advantages of stripping chronopotentiometry (SCP) and stripping chronopotentiometry at scanned deposition potential (SSCP) for trace metal speciation analyses by using thin-film mercury screen-printed electrodes (TMF-SPE). At first, the SCP parameters were optimised for TMF-SPE, in order to reach the complete depletion regime. It has been shown that a stripping current higher than or equal to 10 A allows this regime to be attained without removing oxygen from the solution. Then, these analytical conditions were used for the construction of SSCP curves for Cd-PDCA and Cd-NTA. When the concentration of free ligand in solution was known, the knowledge of the model describing the SSCP curves in absence and presence of a complex and the use of an effective fitting tool enabled estimating the stability constant and the rate constants for complexation. Further studies with complexes of restricted mobility are however necessary to assess the usefulness of this procedure to also estimate the diffusion coefficient of the complexes. Besides, this study showed that this approach was valid even when ligands were not in excess at the electrode during stripping.

In this work, we have undertaken the construction of a screen-printed electrode modified by a specific membrane to protect the working surface from interferences during the analysis of trace metals by anodic stripping voltammetry. Different crown-ethers selected for their metals affinity have been incorporated into a membrane then deposed on the working surface of the electrode. Each modified electrode has been first tested in an acidified KNO 3 10 -1 mol L -1 solution (pH 2) doped by free Cd 2+ and Pb 2+ ions. The response and selectivity of the modified electrodes have been investigated according to different parameters: (i) the substrates (commercial ink or carbon based homemade ink), (ii) the electrode support (polystyrene or transparency film) and (iii) crown-ethers nature (dibenzo-24-crown-8 and tetrathiacyclododecane 12-crown-4). The influence of the substrate on the response of the electrode is clearly demonstrated. Homemade ink appears as the most appropriate substrate to modify the working surface of the screen-printed electrode by a crown-ether based membrane. The effect of the composition of the membrane has been shown too. The best membrane developed showed a detection limit of 0.6 × 10 -8 mol L -1 for Cd and 0.8 × 10 -8 mol L -1 for Pb and a quantification limit of 10 -8 mol L -1 for Cd and 2 × 10 -8 mol L -1 for Pb. This method, which integrates the extraction, preconcentration and measurement, was successfully applied to environmental samples without pretreatment.

This paper presents the characterization and optimization of biosensors based on graphite-epoxy which incorporates the enzyme acetylcholinesterase (AChE). By means of advanced electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), the characterization and optimization of graphite-epoxy-AChE biosensors have been performed. In order to obtain sensitive electrodes, the optimal composition of the transducer material (graphite-epoxy-enzyme ratio) was studied. The optimization of the conductive particles distribution inside the biomaterial has allowed an improvement of the electrochemical properties. Optimal composition guarantees improving electrochemical properties required, such as high electron-transfer rate, high signal-to-noise ratio, and suitable sensitivity. The optimal biocomposite composition range was obtained between 16% and 17% of graphite and 0.12% of AChE. The biosensors were applied to the analysis of different pestici...

A disposable amperometric biosensor for lactic acid has been constructed based on the immobilisation of the enzyme L-lactate dehydrogenase (LDH) and its cofactor nicotinamide adenine dinucleotide (NAD) using a cellulose acetate (CA) membrane cast in situ. These components were deposited onto a screen-printed carbon electrode containing 2% Meldola's Blue (by weight of carbon). Sensor construction was optimised, the final biosensor contained 10 units of LDH, 60 pg of NAD+ and used a membrane cast from a 1% CA solution. The optimum solution for lactate measurement was found to consist of 0.5 mol dmP3 phosphate buffer, pH 8. The optimum temperature was 32°C. The relative standard deviation for a single batch of electrodes was found to be 8.7%.

A disposable amperometric biosensor for lactic acid has been constructed based on the immobilisation of the enzyme L-lactate dehydrogenase (LDH) and its cofactor nicotinamide adenine dinucleotide (NAD) using a cellulose acetate (CA) membrane cast in situ. These components were deposited onto a screen-printed carbon electrode containing 2% Meldola's Blue (by weight of carbon). Sensor construction was optimised, the final biosensor contained 10 units of LDH, 60 pg of NAD+ and used a membrane cast from a 1% CA solution. The optimum solution for lactate measurement was found to consist of 0.5 mol dmP3 phosphate buffer, pH 8. The optimum temperature was 32°C. The relative standard deviation for a single batch of electrodes was found to be 8.7%.

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO 2 as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-␤-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-␤-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases. The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min-1 , injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 mol L-1 glucose in free form. The limit of detection (3σ)is1mol L-1 glucose. A concentration of 100 mol L-1 yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase). Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.

A simple biosensor constructed by bulk-modification of carbon ink with manganese dioxide as a mediator was investigated for its ability to serve as amperometric detector for L-ascorbic acid in hydrodynamic mode. The sensor could be operated at pH 5.0 (0.05 M phosphate buffer) and exhibited excellent reproducibility and stability. Optimization of measurement parameters such as applied working potential and pH value were studied in detail. The screen printed electrode exhibited a linear amperometric increase with the concentration of L-ascorbic acid from 50 mg L -1 to 250 mg L -1 and gave a (LOD = 3σ) detection limit of 0.2 mg L -1 (1.172 µmol L -1 ). The manganese dioxide modified screen printed electrode shows long term stability.

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO 2 as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-␤-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-␤-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases. The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min -1 , injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 mol L -1 glucose in free form. The limit of detection (3σ) is 1 mol L -1 glucose. A concentration of 100 mol L -1 yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase). Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.

exclusion assay showed that addition of carboxylate anions on the surface of the polymer reduced the electrostatic binding affinity of DNA in high percentages of grafting but the nanoparticles still could form stable complexes with DNA. Altered binding affinity and surface charge reduction also changed the buffering capacity of PEI. The efficacy of these nanoparticles for delivery of plasmid DNA was investigated on Neuro2A cells. Conclusion: Some of the novel gene carriers, were successfully applied for in vitro transfection and could easily compete with both unmodified PEIs and the current 'golden standard' branched polyethylenimine with an average Mw of 25 kDa (PEI25b), having the advantage of being much less toxic. The resulting polymers displayed a very promising basis for the development of further powerful gene carriers.

exclusion assay showed that addition of carboxylate anions on the surface of the polymer reduced the electrostatic binding affinity of DNA in high percentages of grafting but the nanoparticles still could form stable complexes with DNA. Altered binding affinity and surface charge reduction also changed the buffering capacity of PEI. The efficacy of these nanoparticles for delivery of plasmid DNA was investigated on Neuro2A cells. Conclusion: Some of the novel gene carriers, were successfully applied for in vitro transfection and could easily compete with both unmodified PEIs and the current 'golden standard' branched polyethylenimine with an average Mw of 25 kDa (PEI25b), having the advantage of being much less toxic. The resulting polymers displayed a very promising basis for the development of further powerful gene carriers.

In this work, cobalt hexacyanoferrate (CoHCF) modified screen-printed electrodes were developed and characterised electrochemically. The effect of different cations was investigated showing a more reversible system with a well-defined peak around +0.35 V vs. Ag/AgCl when Na + was used as cation in the supporting electrolyte. The transfer coefficient (a) and the apparent charge transfer rate constant (k s) for electron transfer between the electrode and the CoHCF layer was calculated. The electrocatalytic behaviour of CoHCF towards oxidation of enzymatically generated thiocholine was thoroughly investigated. Cyclic voltammetry experiments performed in thiocholine solution showed the classical shape of a mediated redox system. The diffusion constant of thiocholine was estimated using chronoamperometry. Also, the catalytic rate constant k of thiocholine at CoHCF-SPE was determined. The current due to thiocholine mediated oxidation was then evaluated in batch amperometric mode at +0.5 V vs. Ag/AgCl obtaining a linear range (5 Â 10 À7-1 Â 10 À5 mol L À1) with a low detection limit and a high sensitivity equal to 5 Â 10 À7 mol L À1 and 435 mA mol À1 L cm À2 , respectively.

Lipase activity against triacylglycerols has been measured using an amperometric enzyme biosensor based on glycerol dehydrogenase/NADH oxidase. A Prussian Blue modified screen-printed electrode was selected as substrate for the two immobilised-enzyme systems due to their higher operative stability reported in previous works. Various parameters such as cofactor (flavin mononucleotide FMN) concentration (1 mM), NAD + coenzyme concentration (2 mM), pH effect (phosphate buffer pH 6 to 8, Tris buffer pH 8-10) response time and storage stability were evaluated and optimised. The glycerol biosensor was then investigated for lipase activity. The system was challenged against an olive or sunflower oil real samples in order to detect fatty acids and the results were compared with those provided either by the manufacture or reference methods with good agreement.

A method based on a thiol-disulfide exchange reaction is proposed for glutathione detection. The method utilises a reaction between glutathione and an excess of the disulfide cystamine which produces an equimolar concentration of the thiol cysteamine. This latter is then detected at Prussian Blue modified screen printed electrodes at an applied potential of 200 mV versus Ag/AgCl. First the cysteamine analytical parameters were optimised, resulting in a detection limit of 10 −6 mol l −1 and a linear range up to 10 −4 mol l −1. Reproducibility (R.S.D. = 7%, n = 6) and stability (more than 30 measurements with the same electrode) were satisfactory. Then the reaction between the disulfide cystamine and the thiol glutathione was optimised and a pH of 7.4 with a concentration of cystamine of 10 −2 mol l −1 was chosen as the best conditions in terms of reaction rate and sensor sensitivity. Glutathione was then measured under the optimised conditions giving a detection limit of 2 × 10 −6 mol l −1 and a linear range up to 5 × 10 −4 mol l −1. Blood samples were also tested in order to determine the recovery of the method. Recoveries between 92 and 103% were observed for glutathione concentrations in blood ranging from 0.5 to 3 × 10 −3 mol l −1 .

An overview is presented which summarizes our accomplishment in the development of sensors and biosensors based on heterogenous carbon electrodes modified with manganese dioxide. Brief account of each sensor and biosensor has been given and example of real sample applications provided where appropriate.

(English) Amperometric biosensors for bonded glucose were fabricated using screen printed carbon elecrode bulk modified with manganese dioxide onto which glucosidase and glucose oxidase were immobilized by Nafion film entrapment. Three methods of enzyme immobilization were performed (layering, mixing and sequencing of enzyme solutions). The analytical performance of the biosensor prepared by different enzyme immobilization methods was assessed in a flow injection mode using three sugar ...

Hydrogen peroxide (H2O2) has wide applications in industrial processes as a universal oxidant, and it is also a very important intermediate in environmental and biological reactions. The monitoring of H2O2 with a reliable, rapid and economic method is of great significance for numerous processes. The determination of H2O2 has been an important project from the last century to the present (Schachl et al. 1997; Wang et al. 2003).

Low-cost disposable immunosensors were produced by covalent binding of Protein A or G on graphite-polystyrene screen-printed electrodes, and they were used in a fully automated flow-injection analysis (FIA) system, allowing the kinetics of IgG binding to Protein A or G to be improved by forced convection. The displacement of rabbit IgG bound to Protein A or G by mouse IgG isotypes (IgG 1 or IgG 2a) was studied. A FIA immunoassay of mouse IgG 2a was performed at a Protein A-based immunosensor with a good sensibility (down to 0.02 g ml −1) and a total assay time of 19 min. It was shown that the immunosensor combines the advantages of being reusable for more than 30 assay cycles in flow-injection analysis, and disposable when necessary.

A theoretical model of mass transfer kinetics was developed for investigating the accumulation of cationic compounds at an anionic surfactant-doped screen-printed electrode. It was extended to an enzyme-generated cationic product for the indirect determination of alkaline phosphatase (AP). The model takes into account the analyte depletion, the kinetics of the ion-exchange reaction-diffusion and the kinetics of the enzymatic reaction. The relationship between the ion-exchange voltammetric anodic peak current and the enzyme incubation/accumulation time for a given concentration of AP was established and the validity of the theoretical model was verified experimentally using a new AP substrate/product couple. It was shown that the theoretical and experimental data are in agreement. The combination of the catalytic enzyme generation of the cationic product with its simultaneous preconcentration at a cation-exchanger-doped electrode allows one to envision the indirect determination of AP at femtomolar levels.

Low-cost disposable immunosensors were produced by covalent binding of Protein A or G on graphite-polystyrene screen-printed electrodes, and they were used in a fully automated flow-injection analysis (FIA) system, allowing the kinetics of IgG binding to Protein A or G to be improved by forced convection. The displacement of rabbit IgG bound to Protein A or G by mouse IgG isotypes (IgG 1 or IgG 2a) was studied. A FIA immunoassay of mouse IgG 2a was performed at a Protein A-based immunosensor with a good sensibility (down to 0.02 g ml −1) and a total assay time of 19 min. It was shown that the immunosensor combines the advantages of being reusable for more than 30 assay cycles in flow-injection analysis, and disposable when necessary.

This paper reports the development of a novel detection method, based on the coupling of a biosensor measuring device and a flow-injection system, using the enzyme formaldehyde dehydrogenase and a Os(bpy) 2-poly(vinylpyridine) (POs-EA) chemically modified screen-printed electrode. The sensor can detect 30 ng ml − 1 of formaldehyde in aqueous solution (corresponding to sub-ppb atmospheric concentrations of formaldehyde). The sensor is selective, inexpensive, stable over several days, and disposable, as well as simple to manufacture and operate. The system described here can easily be adapted to other substrates using their corresponding dehydrogenases.

A disposable screen-printed multi channel taste sensor composed of several types of lipid as transducers and a computer as data analyzer could detect taste in a manner similar to human gustatory sensation. The disposable taste sensor was used to measure the electrical potential resulted from the interaction between lipid membranes and taste substances. In the present study, two types of packaged commercial milk, the ultra high temperature (UHT) and the pasteurized milk were tested. It was found that the disposable taste sensor is capable to discriminate reliably between fresh and spoiled milk and to follow the deterioration of the milk quality when it is stored at room temperature based on a pattern recognition principle namely Principle Component Analysis (PCA). This research could provide a new monitoring method ideally for simple and cheap decentralized testing for controlling the quality of milk, which may be of great use in the dairy industries.

In this study, a portable electronic tongue was developed and successfully used to distinguish and to discriminate quality of saffron samples. The proposed system consisted of an array of voltammetric sensors based on screenprinted electrodes (SPE), where the working electrodes were of different chemical natures (e.g. carbon, gold and modified carbon electrode). Moreover, the carbon electrodes were chemically modified by electrocatalytic copper phthalocyanine derivatives. The electrodes were immersed in saffron infusions to produce complex voltammetric curves that were characterised for each saffron sample. The electrochemical signals provided by the array showed good correlations with the data obtained from traditional chemical analysis, in particular with the kaempferol, a flavonol with antioxidant activity. The calibration model was optimised using more meaningful description of factors. Finally, discriminant analysis showed that the proposed e-tongue based on SPEs modified with phthalocyanine is useful for discrimination of saffron samples with different qualities. All of these results reveal that proposed e-tongue has a high potential for saffron quality control due to its very simple sample preparation and also its fast response.

881-882A new hydroxyl-ion selective poly(vinyl chloride)- membrane electrode based on chlorpromazine base in the presence of sodium tetraphenyl borate has been prepared with dioctylphthalate as a plasticizer. The performance characteristics of the electrode have been studied. It exhibits a good Nernstian response at room temperature, over a relatively wide range of hydroxyl ion concentrations and is highly selective toward a large number of inorganic anions

This paper reports the interest of the novel 4-carboxyphenyl-grafted screen-printed electrodes (4-CP-SPEs) for sub-nanomolar analysis of uranium in water samples. Electrodes were easily prepared via electrochemically reduction of the corresponding diazonium salt. The stability of the grafted layer has been clearly demonstrated. Uranium detection was then achieved by immersing the grafted electrode into the sample solution, followed by the electrochemical measurement of adsorbed U(VI) by square wave voltammetry. Adsorption time was investigated so as to find the best compromise between analysis time, repeatability and reproducibility. Limit of detection and quantitation reached 7 × 10 −10 and 2 × 10 −9 mol L −1 , respectively. Moreover, interference study was conducted with Zn(II), Cd(II), Pb(II) and Cu(II); no major interference was established. 4-CP-SPEs were finally applied for uranium determination in estuarine water demonstrating the convenience of these electrodes for environmental analysis.

PCBs are among the most persistent and widely distributed pollutants in the global ecosystem and therefore it is of great importance for both human and environmental health to develop practical analytical systems to detect them. In this context, this work presents the application of an electrochemical immunosensor based on Screen-Printed Carbon-based Electrodes as transducers with antibody-coated magnetic microparticles as a solid phase. The immunoassay was based on direct competition between the analyte present in the samples and an alkaline phosphatase-labeled tracer. The product of the enzymatic reaction between AP and its substrate (a-naphthyl phosphate) was detected using differential pulse voltammetry. Sample extraction and clean-up was achieved using Solid Phase Extraction. Detection of low concentrations PCB was achieved and the method was shown to be applicable to both skimmed and whole milk. SPE was shown to improve the analysis.

Novel cost-effective screen-printed potentiometric platforms for simple, fast, and accurate assessment of Fluoxetine (FLX) were designed and characterized. The potentiometric platforms integrate both the FLX sensor and the reference Ag/AgCl electrode. The sensors were based on the use of 4′-nitrobenzo-15-crown-5 (ionophore I), dibenzo-18-crown-6 (ionophore II), and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) (ionophore III) as neutral carriers within a plasticized PVC matrix. Multiwalled carbon nanotubes (MWCNTs) were used as a lipophilic ion-to-electron transducing material and sodium tetrakis [3,5-bis(trifluoromethyl)phenyl] borate (NaTFPB) was used as an anionic excluder. The presented platforms revealed near-Nernstian potentiometric response with slopes of 56.2 ± 0.8, 56.3 ± 1.7 and 64.4 ± 0.2 mV/decade and detection limits of 5.2 × 10−6, 4.7 × 10−6 and 2.0 × 10−7 M in 10 mM Tris buffer solution, pH 7 for sensors based on ionophore I, II, and III, respectively. All measurements w...

A novel mathematical model is presented of the liquid transfer process encountered during screen printing, enabling the prediction of the volume of liquid removed from a mesh and printed on a substrate with reasonable accuracy. It is based on the key assumption that free surface effects dominate and the printed liquid is pulled out of, rather than flows from, the mesh. The model is validated against an extensive range of benchmark data from both on-and off-screen printing trials. The agreement is found to be remarkably good. In addition, the model is able to offer considerable insight to practitioners and liquid manufacturers alike-a key result being that the screen printing process can be made essentially independent of many of the setup parameters in the operating range adopted by most practitioners.

Pyrolyzed photoresist carbon electrodes modified with bismuth (Bi‐PPCEs) were prepared and used for the determination of trace levels of chromium. In order to lower the detection limit, the choice of the supporting electrolyte concentration and electroanalytical parameters were optimized. The adsorptive cathodic stripping voltammetric determination of Cr(VI) at Bi‐PPCE was selective even in the presence in Cr(III). A detection limit of 0.1 µg L−1 was obtained after 60 s preconcentration. After oxidation with UV light and oxygen, all chromium species were oxidized to Cr(VI) and the total inorganic Cr determination is possible. Finally, Bi‐PPCE was applied to trace Cr(VI) analysis in real samples such as waste water and tap water.

Gold nanoelectrodes ensembles (NEEs) have been prepared by electroless plating of Au nanoelectrode elements within the pores of a microporous polycarbonate template membrane. Cyclic voltammograms recorded in (ferrocenylmethyl) trimethylammonium hexafluorophosphate (FA + PF 6 −) solutions showed that these NEEs operate in the "total-overlap" response regime, giving well resolved peak shaped voltammograms. Experimental results show that the faradaic/background currents ratios at the NEE are independent on the total geometric area of the ensemble, so that NEE can be enlarged or miniaturized at pleasure without influencing the very favorable signal/noise ratio. Differential pulse voltammetry (DPV) at the NEE is optimized for direct determinations at trace levels. DPV at NEE allowed the determination (with no preconcentration) of trace amounts of FA + , with a detection limit of 0.02 M. The use of NEE and DPV in cytochrome c (cyt c) solutions showed the possibility to observe the direct electrochemistry of submicromolar concentration of the protein, even without the need of adding any promoter or mediator.

Gold nanoelectrode ensembles (NEEs) are prepared by electroless plating of Au nanoelectrode elements within the pores of a microporous polycarbonate template membrane. The surfaces of these NEEs and also the inner morphology of the gold nanofibers inside the membrane pores are imaged by scanning and transmission electron microscopy. The use of NEEs in micromolar cytochrome c (cyt c) solutions reveals the possibility of observing the direct electrochemistry of the protein, without the need of any promoter or mediator. Cyt c detection limits at NEEs are 1.0 lM by cyclic voltammetry and 0.03 lM by differential pulse voltammetry. The main difference between the voltammetric signals recorded at NEEs in the absence and in the presence of the promoter 4,4 0-bipyridyl is the more extended dynamic range obtained in the latter case. Quartz crystal microbalance measurements at gold-coated quartz crystals show that, in the absence of promoter, adsorption problems are responsible for the poisoning of the electrode surface. Such adsorption is, however, concentration dependent, so that in diluted solutions (cyt c concentration 6 20 lM) it becomes negligible. Experimental evidence indicates that the capability of NEEs to detect the direct electrochemistry of cyt c even in the absence of promoters is related to their peculiar property of furnishing well-resolved voltammetric signals in diluted solutions, where this unwanted adsorption is eliminated.

A development of disposable strip-type galactose sensor for point-of-care testing (POCT) was studied, which was constructed using screen-printed carbon electrodes. Galactose levels were determined by the redox reaction of galactose oxidase in the presence of potassium ferricyanide as an electron transfer mediator in a small sample volume (i.e., less than 1 µL). The optimal performance of biosensor was systematically designated by varying applied potential, operating pH, mediator concentration, and amount of enzyme on the electrode. The sensor system was identified as a highly active for the galactose measurement in terms of the sensitivity (slope = 4.76 ± 0.05 nA/µM) with high sensor-to-sensor reproducibility, the linearity (R 2 = 0.9915 in galactose concentration range from 0 to 400 µM), and response time (t 9 5 % = <17 s). A lower applied potential (i.e., 0.25 V vs. Ag/AgCl) allowed to minimize interference from readily oxidizable metabolites such as ascorbic acid, acetaminophen, uric acid, and acetoacetic acid. The proposed galactose sensor represents a promising system with advantage for use in POCT.

Potentiometric properties of cholic and deoxycholic acid derivatives substituted with various ion-recognizing moieties, such as dithiocarbamate, bipyridyl, glycolic and malonic diamides, urea and thiourea, and trifluoroacetophenons (TFAP), have been studied using solvent polymeric membranes. The dithiocarbamate and bipyridyl group containing ionophores exhibit high silver ion selectivity. The cholic acid derivatized with glycolic diamides exhibited high calcium selectivity, but its complex formulation constant was 10 5 times smaller than that of ETH 1001. The reduced calcium binding ability of the glycolic diamide-substituted ionophore was advantageous for eliminating anionic interference. The bi-or tripodal malonic diamide-substituted ionophores exhibited substantially increased magnesium selectivity. Anion-selective ionophores have been designed by substituting urea and thiourea group containing chains to the hydroxyl linkers of chenodeoxycholic acid frames; their selectivity closely followed the sequence of Hoffmeister series, except the unusually large response of the thiourea-substituted ionophore to sulfate. The most successful examples of cholic or deoxycholic acid frame-based ionophores are those functionalized with two carbonate-selective TFAP groups: bipodal TFAP groups behaves like a tweezers for the incoming carbonate, and exhibit analytically interference free and quantitative responses to the carbonate in serum and seawater samples.

We consider flow systems that have been utilized for small-scale biomolecular computing and digital signal processing in binary-operating biosensors. Signal measurement is optimized by designing a flow-reversal cuvette and analyzing the experimental data to theoretically extract the pulse shape, as well as reveal the level of noise it possesses. Noise reduction is then carried out numerically. We conclude that this can be accomplished physically via the addition of properly designed well-mixing flow-reversal cell(s) as an integral part of the flow system. This approach should enable improved networking capabilities and potentially not only digital but analog signal-processing in such systems. Possible applications in complex biocomputing networks and various sense-and-act systems are discussed.

A novel detection method for organophosphate neurotoxins has been described, based on the fluorescence quenching of a Coumarin derivative. These dyes are similar in structure to some organophosphates (OPs), and they fluoresce in the blue-green region of the spectra. This methodology has been utilized for the detection of organophosphates whose hydrolysis product is p-nitrophenol by using an enzyme, organophosphorus hydrolase (OPH). Coumarin1 in the presence of p-nitrophenol results in a quenching of fluorescence, providing a direct measure of the concentration of p-nitrophenol present in the sample. The decrease in fluorescence intensity is proportional to the paraoxon concentration in the range of 7.0 × 10 −7-1.7 × 10 −4 M. The specificity of this sensing application for p-nitrophenyl substituent OPs has also been demonstrated. OPs are a class of synthetic organic pesticides which generally have a short residual life and can cause numerous acute and chronic health effects. They have been an integral part of the agricultural industry for the past several decades due to their target specificities and selectable toxicities. The toxic nature of these compounds can be attributed to the species-specific inhibition of acetylcholinesterase (AChE), an important enzyme responsible for the regeneration of neural synaptic function. In addition to their wide agricultural and urban usage, they have also been exploited for the development of neurological chemical warfare agents. Currently available technologies for OP detection include sol-gel thin films, screen printed electrodes, acoustic patterning, gas chromatography-mass spectrometry, and various other intricate techniques that have limited field applicabilities. This optically-based approach promises much simpler and more direct detection capabilities.

Potentiometry is extensively studied by researchers as one of the electrochemical methods due to its multiple advantages. Until today, thousands of potentiometric sensors have been developed and applied successfully in many fields such as medicine, environmental monitoring, agriculture, industry and pharmaceutical sciences. Clinical drug analyses and determination of drugs in biological samples are highly important from a medical point of view. These analyses are carried out using various analytical devices including potentiometric sensors. These potentiometric sensors are superior to other devices in terms of several performance parameters, and thus present a good alternative for researchers. Using potentiometric sensors, very successful results in the identification of drug molecules in body fluids have been obtained and reported in the literature up to now. In this study, we review potentiometry-based sensors developed for the determination of drug molecules in various biological samples such as blood serum and urine, and touch upon their performance features in these applications.

Carbon nanofibers (CNFs) are fiber-structured nano-sized carbon materials, which have excellent mechanical, thermal and electrical properties. CNFs possess a wide range of application especially in biorecognition area. In this study, we developed an indicator-free voltammetric biosensor for detection of miRNA-34a target RNA by using carbon nanofiber enriched disposable screen printed electrodes (CNF-SPEs). The sensitive and selective recognition of miRNAs has been an attractive topic due to they have been defined as small RNAs and play major roles in regulating the translation and degradation of messenger RNAs. The characterization of CNF-SPEs in contrast to unmodified ones was firstly performed by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) techniques. The amino linked DNA probe, that was the complementary sequence of miRNA-34a, was immobilized onto the surface of CNF-SPEs. After measuring the guanine oxidation signal measured by differential pulse voltammetry (DPV), the detection of sequence-selective hybridization was then investigated between probe and miRNA-34a RNA target, or other miRNA sequences; miRNA-15a, or miRNA-660, which were chosen as noncomplementary sequences (NC). The detection limit was corresponded to 10.98 μg/mL (54 pmol in 35 μL sample) in the linear concentration range of target miRNA-34a from 25 to 100 μg/mL by using CNF-SPEs. The features of this present study was comprehensively discussed by means of the unique characteristics of single-use CNF-SPEs and importance of miRNA monitoring.

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HC1 and H 2 O 2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators.