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Early diagnosis of bacterial infections is crucial to improving survival rates by enabling treatment with appropriate antibiotics within the first few hours of infection. This paper presents a highly sensitive amperometric biosensor for the detection of several pathogenic bacterial cells in blood plasma around 30 min. The proposed device is based on an electropolymerized self-assembled layer on gold nanoparticles operated in a portable nano-sieving microfluidic system (NS-MFS). The redox-active gold nanoparticles (raGNPs) enhanced the electrical conductivity and provided a greater number of electrochemically active molecules for sensing, while improving resistance to the fouling of sensors by oxidation products in blood plasma. The detection limit of the device has been shown to reach 10 CFU/mL for Pseudomonas aeruginosa and Staphylococcus aureus spiked in plasma. The dynamic range of the sensing system falls between 10 and 105 CFU/mL in a buffer solution by cyclic voltammetry (CV) measurements. The results demonstrated that the raGNPs/NS-MFS can successful detect P. aeruginosa and S. aureus in human plasma, and is very useful for the diagnosis of bacteremia from clinical samples. • We proposed a raGNPs/NS-MFS amperometric device to detect pathogenic bacteria in human plasma. • The raGNPs/NS-MFS amperometric device provide 5 orders dynamic range of the sensing. • raGNPs does not require electrochemical transfer media or special catalysts for signal enhancement. • A chip-based filtration system using an array of MWCNT nanopillars to capture, concentrate and purification bacteria pretreatment procedures. [ABSTRACT FROM AUTHOR]

Abstract Enzymatic and non-enzymatic amperometric glucose sensors based on nanostructured Au-Ni alloy were prepared and compared in their performance. The hierarchically structured Au-Ni surface was merely used for the non-enzymatic glucose sensor, while glucose oxidase attached poly-3′(benzoic acid) −2,2′:5′,2′- terthiophene (pTBA) formed on the alloy surface was used as the enzymatic sensor. The fabricated sensor was characterized using surface analysis and electrochemical experiments. In case of the enzymatic sensor, the anodic current of H 2 O 2 generated from the enzyme reaction was used as the analytical signal, while the direct oxidation of glucose was observed on a mere Au-Ni alloy electrode without enzyme immobilization, which shows an excellent catalytic oxidation of glucose even in physiological pH. The potential pulse pretreatment of the sensor surfaces improved the performance, which allowed both the sensors reproducible and reusable (enzymatic sensor: coefficient of variation = 1.82%, n = 5, non-enzymatic: coefficient of variation = 2.93%). The enzymatic biosensor reveals the advantages of increased sensitivity, selectivity, and stability, compared with the non-enzymatic sensor. The linear range of enzymatic sensor was attained from 1.0 µM to 30.0 mM with a detection limit of 0.29 μM. The reliabilities of the sensors were also demonstrated through the glucose analysis in human blood samples, and the result was compared with the commercially available glucometer. Highlights • The performance of enzymatic and non-enzymatic glucose sensors based on hierarchical Au-Ni alloy were compared. • The hierarchical bimetallic alloy gave an increased sensitivity for glucose and H 2 O 2 oxidation in neutral pH. • The enzymatic sensor was more sensitive, selective, and stable than that of non-enzymatic. [ABSTRACT FROM AUTHOR]

Lab-on-a-Chip (LoC) technology has the potential to revolutionize medical Point-of-Care diagnostics. Currently, considerable research efforts are focused on innovative production technologies that will make commercial upscaling of lab-on-chip products financially viable. Printed circuit board (PCB) manufacturing techniques have several advantages in this field. In this paper we focus on transferring a complete IFN-γ enzyme-linked immune-sorbent assay (ELISA) onto a commercial PCB electrochemical biosensing platform, We adapted a commercially available ELISA to detect the enzyme product TMB/H 2 O 2 using amperometry, successfully reproducing the colorimetry-obtained ELISA standard curve. The results demonstrate the potential for the integration of these components into an automated, disposable, electronic ELISA Lab-on-PCB diagnostic platform. [ABSTRACT FROM AUTHOR]

In this work, a sensitive amperometric biosensor for hydrogen peroxide based on synergetic catalysis of hemoglobin and porous Pd@Fe 3 O 4 -MWCNT nanocomposite has been constructed. With attention to the utilities of large surface area and outstanding catalytic performance, Pd@Fe 3 O 4 -MWCNT nanocomposite was employed as the nano-stabilizer for the immobilization of hemoglobin (Hb). The immobilized Hb on the surface of nanocomposite as an electrochemical biosensor efficiently catalyzed the reduction of hydrogen peroxide, amplified the electrochemical signal and enhanced the sensitivity. Results of voltammetry and electrochemical impedance examinations showed that the nanocomposite could enhance the electron conductivity and provide more sites for the immobilization of Hb. A linear response from 0.2–500 µM with detection limit of 0.063 µM for hydrogen peroxide was achieved. The apparent Michaelis–Menten constant K app M value was 21 µM. Thus, the nanocomposite could be applied for fabrication of a third generation biosensor for hydrogen peroxide with high sensitivity, selectivity and low detection limit. The excellent performance of the biosensor indicated its promising prospect as a valuable tool in simple and fast hydrogen peroxide detection in environmental and clinical applications. [ABSTRACT FROM AUTHOR]

Novel self-assembled dipeptide–gold nanoparticle (DP–AuNP) hybrid microspheres with a hollow structure have been prepared in aqueous solution by a simple one-step method. Diphenylalanine (FF) dipeptide was used as a precursor to form simultaneously peptide spheres and a reducing agent to reduce gold ions to gold nanoparticles in water at 60 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that formed AuNPs were localized both inside and on the surface of the dipeptide spheres. Horseradish peroxidase (HRP) as a model enzyme was further immobilized on the dipeptide–AuNP hybrid spheres to construct a mediate H 2 O 2 amperometric biosensor. UV–vis spectroscopy showed that the immobilized HRP retained its original structure. Cyclic voltammetry characterization demonstrated that the HRP/dipeptide–AuNP hybrid spheres modified glassy carbon electrode showed high electrocatalytic activity to H 2 O 2 . The proposed biosensor exhibited a wide linear response in the range from 5.0×10 −7 to 9.7×10 −4 M with a high sensitivity of 28.3 µA mM −1 . A low detection limit of 1.0×10 −7 M was estimated at S/N =3. In addition, the biosensor possessed satisfactory reproducibility and long-term stability. These results indicated that the dipeptide–AuNP hybrid sphere is a promising matrix for application in the fabrication of electrochemical biosensors due to its excellent biocompatibility and good charge-transfer ability. [ABSTRACT FROM AUTHOR]

A new approach for the one-pot synthesis of reduced graphene oxide-dendritic Pd nanoparticle (rGO-nPd) hybrid material and the development of biosensing scaffold for the amperometric sensing of H2O2 and total cholesterol in human serum are described. In situ reduction of both graphene oxide (GO) and PdCl42− in acidic solution was achieved with Zn to obtain rGO-nPd hybrid material. The oxygen containing functionalities of GO were reduced by the liberated atomic hydrogen in 20min. The formal potential of Zn/Zn2+ and PdCl42−/Pd couples favor the facile reduction of PdCl42−. The in situ produced Pd nanoparticles behave like hydrogen sponge and increase the local concentration of atomic hydrogen. Biosensing platforms for H2O2 and cholesterol in human serum and butter sample were developed using the hybrid material. Amperometric sensing of H2O2 at 0.2nM level without any redox mediator or enzymes in neutral pH is demonstrated. The cholesterol biosensing platform was developed by integrating cholesterol oxidase and cholesterol esterase with the hybrid material. The biosensor is highly sensitive (5.12±0.05μA/μMcm2) and stable with a fast response time of 4s; it could detect cholesterol ester as low as 0.05µM (S/N=3). The biosensor is successfully used for the analysis of total cholesterol in human serum and butter. [ABSTRACT FROM AUTHOR]

This paper describes an innovative amperometric biosensor for the in vitro determination of activity of transketolase from Escherichia coli (TKec) using commercially available TK substrates, namely d-fructose-6-phosphate a physiological donor and glycolaldehyde the best non-phosphorylated acceptor. A galactose oxidase (GAOx) biosensor, based on the immobilization of this enzyme within laponite clay, allows amperometric detection of l-erythrulose released upon TK-catalyzed reaction. A calibration curve has been established from 0.01 to 0.1Uml−1 TKec concentration in solution. These data are comparable to that obtained by a fluorometric method. In order to ensure a higher sensitivity and re-usability of the system, an original bienzymatic sensing system was further developed based on apoenzyme TKec and GAOx separately immobilized on the electrode surface. The inner sensing layer contains GAOx@laponite and the outer layer TKec@layered double hydroxide biohybrid. The biosensor response was validated by the determination of KDapp for thiamine diphosphate, the TK cofactor and the inhibition action of two commercially available products, pyrophosphate, a TK cofactor analog and d-arabinose-5-phosphate, a substrate analog. [ABSTRACT FROM AUTHOR]

The specific detection of biological organics without the use of an enzyme is challenging, and it is crucial for analytical and clinical chemistry. We report specific nonenzymatic bilirubin detection through the catalytic oxidation of bilirubin molecule on the Nafion/Mn-Cu surface. The catalytic ability, true surface area, morphology, crystallinity, composition, and oxidation state of the sensor surface were assessed using voltammetry, coulometry, XPS, XRD, Brunauer-Emmett-Teller (BET), SEM, EDXS, and TOF-SIMS experiments. The results showed that the surface was composed of microporous Mn-Cu bimetallic crystal in flake shape with a large BET surface area (3.635 m2g-1), where the surface area and crystallinity mainly affected the sensor performance. Product analysis of the catalytic reaction on the sensor probe revealed a specific two-electron oxidation of dipyrromethane moiety to dipyrromethene in the bilirubin molecule. Experimental variables affecting the analysis of bilirubin were optimized in terms of probe composition, temperature, pH, and potential. At the optimized condition, the dynamic range was between 1.2µM and 0.42mM, which yielded the equation of ΔI (µA)=(1.03±0.72)+(457.0±4.03) [C] (mM) with 0.999 of correlation coefficient, and the detection limit was 25.0±1.8nM (n=5, k=3). The stability test, interference effects, and analysis of real clinical samples, human whole blood and certified serum samples were demonstrated to confirm the reliability of the proposed bilirubin sensor. [ABSTRACT FROM AUTHOR]

A novel amperometric biosensor for catechol was developed using the layer-by-layer (LbL) self-assembly of positively charged hexadecyltrimethylammonium stabilized gold nanocubes (AuNCs), negatively charged poly(sodium 4-styrenesulfonate) and tyrosinase on a screen printed carbon electrode (SPCE). A carboxylic acid terminated alkanethiol assembled on electrochemically deposited Au nanoparticles on a SPCE was used as a platform for LbL assembly. Each SPCE sensor surface was terminated with tyrosinase and the electrocatalytic response due to the tyrosinase reaction with catechol was measured using cyclic voltammetry and square wave voltammetry (SWV). The effect of introducing AuNCs into the LbL assembly to further enhance the catechol detection performance was then investigated by comparing the SWV results to those from biosensors created using both the tyrosinase modified LbL assembly in the absence of NCs and the covalent attachment of tyrosinase. A wide dynamic range from 10 nM to 80μM of catechol with an excellent sensitivity of 13.72 A/M and a detection limit of 0.4nM were both achieved alongside a good selectivity and reproducibility for the AuNC-modified electrodes. As a demonstration, the optimized biosensor design was applied to determine catechol concentrations in tea samples. [ABSTRACT FROM AUTHOR]

Abstract: A sensitive amperometric acetylcholinesterase (AChE) biosensor, based on SnO2 nanoparticles (SnO2 NPs), carboxylic graphene (CGR) and nafion (NF) modified glassy carbon electrode (GCE) for the detection of methyl parathion and carbofuran has been developed. The nanocomposites of SnO2 NPs and CGR was synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Chitosan (CS) was used to immobilize AChE on SnO2 NPs–CGR–NF/GCE and to improve electronic transmission between AChE and SnO2 NPs–CGR–NF/GCE. NF was used as the protective membrane for the AChE biosensor. The SnO2 NPs–CGR–NF nanocomposites with excellent conductivity, catalysis and biocompatibility offered an extremely hydrophilic surface for AChE adhesion. The AChE biosensor showed favorable affinity to acetylthiocholine chloride (ATCl) and could catalyze the hydrolysis of ATCl with an apparent Michaelis–Menten constant value of 131μM. The biosensor detected methyl parathion in the linear range from 10−13 to 10−10 M and from 10−10 to 10−8 M. The biosensor detected carbofuran in the linear range from 10−12 to 10−10 M and from 10−10 to 10−8 M. The detection limits of methyl parathion and carbofuran were 5×10−14 M and 5×10−13 M, respectively. The biosensor exhibited low applied potential, high sensitivity and acceptable stability, thus providing a promising tool for analysis of pesticides. [Copyright &y& Elsevier]

Abstract: The rapid determination of trace phenolic compounds is of great importance for evaluating the total toxicity of contaminated water samples. Nowadays, electrochemical tyrosinase (Tyr) based biosensors constitute a promising technology for the in situ monitoring of phenolic compounds because of their advantages such as high selectivity, low production cost, promising response speed, potential for miniaturization, simple instrumentation and easy automatization. A mediator-free amperometric biosensor for phenolic compounds detection based on the combination of bismuth nanoparticles (BiNPs) and Tyr for phenol detections will be hereby reported. This is achieved through the integration of BiNPs/Tyr onto the working electrode of a screen printed electrode (SPE) by using glutaraldehyde as a cross-linking agent. BiNPs/Tyr biosensor is evaluated by amperometric measurements at –200mV DC and a linear range of up to 71μM and 100μM and a correlation coefficient of 0.995 and 0.996 for phenol and catechol, respectively. The very low DC working potential ensures the avoidance of interferences making this biosensor an advantageous device for real sample applications. In addition, the response mechanism including the effect of BiNPs based on electrochemical studies and optical characterizations will be also discussed. The obtained results may open the way to many other BiNPs applications in the biosensing field. [Copyright &y& Elsevier]

Abstract: A novel l-arginine-selective amperometric bi-enzyme biosensor based on recombinant human arginase I isolated from the gene-engineered strain of methylotrophic yeast Hansenula polymorpha and commercial urease is described. The biosensing layer was placed onto a polyaniline–Nafion composite platinum electrode and covered with a calcium alginate gel. The developed sensor revealed a good selectivity to l-arginine. The sensitivity of the biosensor was 110±1.3nA/(mMmm2) with the apparent Michaelis–Menten constant (K M app) derived from an l-arginine (l-Arg) calibration curve of 1.27±0.29mM. A linear concentration range was observed from 0.07 to 0.6mM, a limit of detection being 0.038mM and a response time — 10s. The developed biosensor demonstrated good storage stability. A laboratory prototype of the proposed amperometric biosensor was applied to the samples of three commercial pharmaceuticals (“Tivortin”, “Cytrarginine”, “Aminoplazmal 10% E”) for l-Arg testing. The obtained l-Arg-content values correlated well with those declared by producers. [Copyright &y& Elsevier]

Abstract: An amperometric biosensor was proposed for the enantioanalysis of l-lysine. The biosensor is based on the impregnation of l-lysine oxidase in diamond paste. The potential used for the determination of l-lysine was 650mV. The biosensor exhibited a linear concentration range between 1 and 100nmol/L with a limit of detection of 4pmol/L. The selectivity of the biosensor is high over other amino acids, such as l-serine, l-leucine, l-aspartic acid, l-glutamic acid, histamine, glycine. The proposed biosensor can be applied for the determination of l-lysine in serum samples and pharmaceutical compounds. [Copyright &y& Elsevier]

Abstract: An amperometric sequence-specific molecularly imprinted single-stranded oligodeoxyribonucleotide (ss-ODN) biosensor was fabricated and characterised in this study. Using ss-ODN as the template and o-phenylenediamine as the functional monomer, the ODN biosensor was fabricated by an electropolymerisation process on an indium-tin oxide (ITO) coated glass substrate. The template ss-ODN was washed out of the ss-ODN/poly(o-phenylenediamine)(PoPD)/ITO electrode using sterilised basic ethanol-water. The resulting ss-ODN imprinted PoPD/ITO electrode was characterised using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The amperometric responses, i.e., Δi as a function of the target ss-ODN concentration was studied. The biosensor using ss-ODN imprinted PoPD/ITO as the working electrode showed a linear Δ current response to the target ss-ODN concentration within the range of 0.01–300fM. The biosensor showed a sensitivity of 0.62μA/fM, with a response time of 14s. The present novel molecularly imprinted ss-ODN biosensor could greatly benefit in terms of cost-effectiveness, storage stability, ultra sensitivity and selectivity together with the potential for improved commercial genetic sensors. [Copyright &y& Elsevier]

Abstract: A novel strategy of amperometric assay for drug–dsDNA interactions was developed based on an inhibitory effect of antimararial drug (quinacrine) on an electrocatalytic activity of DNA–Cu(II) complex. In this method, a DNA–Cu(II) complex immobilized DNA/polyallylamine(PAA) polyion complex membrane was used as a sensing element. The electrocatalytic activity of a DNA–Cu(II) complex for hydrogen peroxide reduction was reversibly inhibited by electron blocking effect of quinacrine–dsDNA interaction and this inhibitory effect was amplified by the hydrogen peroxide reduction. This phenomenon was utilized for development of a novel amperometric biosensor for DNA-binding drug. From the amperometric current–time curves, the response time of the sensor to 20μM quinacrine was obtained about 20s, and the detection limit of the quinacrine was found to be 10μM estimated to a signal-to-noise ratio of 3.0. Based on the change of steady-state catalytic current, the kinetic analysis of drug–dsDNA interaction can be done in a similar manner of enzyme inhibition, and the binding constant of the quinacrine with DNA can be calculated. This measurement method would be useful for screening of wide variety of DNA-binding drugs and highly toxic pollutants. [Copyright &y& Elsevier]

Abstract: Cerium oxide nanorods (CeO2 NRs) were synthesized without templates through a low cost and simple non-isothermal precipitation method. The structure and morphology of CeO2 NRs were characterized by X-ray diffraction and transmission electron microscopy. The CeO2 NRs films, deposited on indium tin oxide (ITO)-coated glass substrates through electrophoretic deposition, were used for the immobilization of glucose oxidase (GOx). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the CeO2 NRs/ITO and GOx/CeO2 NRs/ITO electrodes. The GOx/CeO2 NRs/ITO electrode exhibits a linear range for the detection of glucose from 2 to 26mM (correlation coefficient: 0.99) at 1–2s response time. Biosensor sensitivity is 0.165μAmM−1 cm−2 with 100μM detection limit. The anti-interference ability of the biosensor was also examined. The mediator-less application of CeO2 NRs for glucose sensing was demonstrated. [Copyright &y& Elsevier]

Abstract: A novel, highly sensitive amperometric biosensor for detection of organophosphorus (OP) compounds has been constructed, based on rat brain acetylcholinesterase (AChE) immobilized onto nanocomposite of ZnS-nanoparticles (ZnSNPs) and poly(indole-5-carboxylic acid) electrodeposited on Au electrode. In the presence of acetylthiocholine chloride (ATCl) as a substrate, ZnSNPs promoted electron transfer reactions at a lower potential and catalyzed electrochemical oxidation of enzymatically formed thiocholine, thus increasing detection sensitivity. Under optimum conditions (phosphate buffer, pH 7.5 and 30°C), the inhibition of AChE by malathion and chlorpyrifos was proportional to their concentrations in the range, 0.1–50nM and 1.5–40nM, respectively. The biosensor determined malathion and chlorpyrifos in spiked tap water samples with a acceptable accuracy (95–100%). The enzyme electrode had long-storage stability (50% retention of initial activity within 2months, when stored at 4°C). [Copyright &y& Elsevier]

Abstract: A simple and highly sensitive method for simultaneous detection of anticancer drugs is developed by integrating the preconcentration and separation steps in a microfluidic device with an amperometric biosensor. An amperometric detection with dsDNA and cardiolipin modified screen printed electrodes are used for the detection of anticancer drugs at the end of separation channel. The preconcentration capacity is enhanced thoroughly using field amplified sample stacking and field amplified sample injection techniques. The experimental parameters affecting the analytical performances, such as pH, temperature, buffer concentration, water plug length, and detection potential are optimized. A reproducible response is observed during multiple injections of samples with a RSD <5%. The calibration plots are linear with the correlation coefficient between 0.9913 and 0.9982 over the range of 2–60 pM. The detection limits of four drugs are determined to be between 1.2 (±0.05) and 5.5 (±0.3) fM. The applicability of the device to the direct analysis of anticancer drugs is successfully demonstrated in a real spiked urine sample. Device was also examined for interference effect of common chemicals present in real samples. [Copyright &y& Elsevier]

Abstract: A bilayer amperometric nitrate biosensor with an integrated permselective layer has been developed for exclusion of inorganic anion and cation interferences. The inner PPy(polypyrrole)–NaR–NADH layer of the biosensor is formed by galvanostatic polymerization of pyrrole (Py) in presence of nitrate reductase (NaR) and nicotinamide adenine dinucleotide (NADH), followed by formation of the outer permselective poly-ortho-phenylenediamine (P-o-PDA) layer by potentiodynamic polymerization of ortho-phenylenediamine (o-PDA). The exclusion efficiency (E eff) of the outer layer in rejecting inorganic cation and anion interferences is evaluated by a new proposed relationship. 73–87% and 47–84% of anion and cation interferences, respectively, were efficiently rejected with the permselective layer. Further improvement in the exclusion efficiency for cations was accomplished by combining the use of the outer layer with the addition of 1mM EDTA into the measurement solution. The addition of EDTA improved the E eff achieved for cation rejection by 10–40% to give net E eff of 89–94%. The inclusion of the outer layer also aided the retention of NaR and NADH in the inner PPy–NaR–NADH layer and, hence, enabled improved amperometric detection of nitrate, achieving a detection limit of 0.20μM and a linear concentration range of 10–500μM with a 3.4%rsd (n =10). [Copyright &y& Elsevier]

Abstract: A rapid and highly sensitive miniaturized amperometric biosensor for the detection of α-ketoglutarate (α-KG) based on a carbon fiber electrode (CFE) is presented. The biosensor is constructed by immobilizing the enzyme, glutamate dehydrogenase (GLUD) on the surface of single carbon fiber modified by co-deposition of ruthenium (Ru) and rhodium (Rh) nanoparticles. SEM and EDX shed useful insights into the morphology and composition of the modified microelectrode. The mixed Ru/Rh coating offers a greatly enhanced electrocatalytic activity towards the detection of β-nicotinamide adenine dinucleotide (NADH), with a substantial decrease in overpotential of ∼400mV compared to the unmodified CFE. It also imparts higher stability with minimal surface fouling, common to NADH oxidation. Further modification with the enzyme, GLUD leads to effective amperometric biosensing of α-KG through monitoring of the NADH consumption. A very rapid response to dynamic changes in the α-KG concentrations is observed with a response time of 6s. The current response is linear between 100 and 600μM with a sensitivity of 42μAM−1 and a detection limit of 20μM. This proof of concept study indicates that the GLUD-Ru/Rh-CFE biosensor holds great promise for real-time electrochemical measurements of α-KG. [Copyright &y& Elsevier]

Abstract: A high-performance amperometric fructosyl valine (FV) biosensor was developed, based on immobilization of fructosyl amino-acid oxidase (FAO) on core–shell magnetic bionanoparticles modified gold electrode. Chitosan was used to introduce amino groups onto the surface of core–shell magnetic bionanoparticles (MNPs). With FAO as an enzyme model, a new fructosyl valine biosensor was fabricated. The biosensor showed optimum response, when operated at 50mVs−1 in 0.1M potassium phosphate buffer, pH 7.5 and 35°C. The biosensor exhibited excellent sensitivity [the detection limit is down to 0.1mM for FV], fast response time (less than 4s), wide linear range (from 0 to 2mM). Analytical recovery of added FV was 95.00–98.50%. Within batch and between batch coefficients of variation were <2.58% and <5.63%, respectively. The enzyme electrode was used 250 times over 3 months, when stored at 4°C. [Copyright &y& Elsevier]

Abstract: Carbon fiber paper (CFP), a material frequently used as the diffusion layer in fuel cells, was found recently to exhibit a potential as an electrode for the development of sensitive, unmediated biosensors. After nitrogen plasma treatment, the CFP exhibited a quasi-reversible behavior to the redox couple (e.g., ferricyanide) with an electron transfer rate constant of 7.2×10−3 cms−1. This rate constant is approximately double that of a Pt-electrode and is much higher than that of many carbon-based electrodes. The unmediated CFP-based tyrosinase biosensor fabricated for this study exhibited an optimal working potential and operating pH value of −0.2V and 6.5, respectively. Compared to other unmediated tyrosinase biosensors, the CFP-based tyrosinase biosensor offers a high sensitivity for the monitoring of phenolic compounds (17.8, 7.1, 5.2 and 3.7μAμM−1 cm−2 for catechol, phenol, bisphenol and 3-aminophenol, respectively). The lowest detection limit for catechol, phenol, bisphenol and 3-aminophenol was 2, 5, 5 and 12nM, respectively. Furthermore, this biosensor exhibited a good repeatability, a fast response time (around 10s), and a wide linear dynamic range of detection for phenolic compounds. [ABSTRACT FROM AUTHOR]

Abstract: A novel non-enzyme glucose amperometric biosensor was fabricated based on biospecific binding affinity of concanavalin A (Con A) for d-glucose on thionine (TH) modified electrode. TH can be covalently immobilized on potentiostatically activated glassy carbon electrode through Schiff-base reaction. Subsequently, the surface-adherent polydopamine film formed by self-polymerization of dopamine attached to TH and afforded binding sites for the subsequent immobilization of Con A molecules via Michael addition and/or Schiff-base reaction with high stability. Thus, a sensing platform for specific detection towards d-glucose was established. The binding of Con A towards d-glucose can be monitored through the decrease of the electrode response of the TH moiety. Due to the high affinity of Con A for d-glucose and high stability of the resulting sensing platform, the fabricated biosensor exhibited high selectivity, good sensitivity, and wide linear range from 1.0×10−6 to 1.0×10−4 M with a low detection limit of 7.5×10−7 M towards d-glucose. [ABSTRACT FROM AUTHOR]

Abstract: We report on the utilization of triangular silver nanoprisms (AgTNPs) to create a highly responsive glucose biosensor. Glucose oxidase (GOD) was simply mixed with AgTNPs and cross-linked on the Pt electrode with chitosan (CHIT) medium by glutaraldehyde. Circular dichroism (CD) and UV-spectrum results show that the activity of GOD was preserved after conjugating with AgTNPs. The current response of modified electrode is 16 times higher than that without AgTNPs. The biosensor showed high sensitivity (67.17μAcm−2 mM−1), low detection limit (1×10−6 M), good storage stability, and high affinity to glucose (K M =3.84mM). A linear calibration plot was obtained in the wide concentration range from 3×10−6 to 3×10−3 M. The excellent performance of the biosensor is attributed to large surface-to-volume ratio and high conductivity of AgTNPs, and good biocompatibility of CHIT, which enhances the enzyme absorption and promotes electron transfer between redox enzymes and the surface of electrodes. [ABSTRACT FROM AUTHOR]

Abstract: This study is focused on possible application of some 1,10-phenanthroline derivatives (PDs) in the development of biosensors and biofuel cells. Differently from some other studies, the PDs that were not involved into structures of metal complexes were investigated. Five PDs [1,10-phenanthroline monohydrate (PMH); 5-nitro-1,10-phenanthroline (5NP); 5-amino-1,10-phenanthroline (5AP), 5-amino,6-nitro-1,10-phenanthroline (5A6NP) and 5,6-diamino-1,10-phenanthroline (56DAP)] were selected for this study. Bioelectrochemical responses of PDs and glucose oxidase (GOX)-modified graphite rod electrodes (GREs) were studied amperometrically and potentiometrically. The best redox mediators for GOX were found on PDs containing amino groups: 5AP and 56DAP. Amperometrical measurements have shown that 5NP derivative was also acting as a redox mediator but activity of 5NP was approximately four times lower than 5AP and three times lower than 56DAP. This study clearly illustrates that some PDs can be applied as redox mediators for oxidases and are suitable for the development of reagent-less biosensors and biofuel cells. Since amino groups can be very easily involved in the formation of chemical bounds, the amino-PDs are interesting compounds for the development of nanobiotechnological tools by bottom-up technique. [Copyright &y& Elsevier]

Abstract: Pyrrole electrooxidation in the presence of weak-acidic anions allows one to locally, rapidly and in single step form on the electrode a pinhole-free very thin layer of overoxidized polypyrrole (OPPy). This membrane could be really useful for the design of amperometric biosensor based on oxidation of H2O2 generated by an oxidase. Indeed, using rotation disk electrode, the apparent diffusion coefficient of H2O2 within this OPPy film was found to be 10−8 cm2 s−1, which corresponds to a fast response time of 0.1ms. Moreover, it is shown that with this system, platinum electrode coated with the very thin OPPy membrane, the H2O2 sensitivity is excellent (700nAμM−1 cm−2) and the H2O2 selectivity relative to potentially interfering species present in biological fluids, such as ascorbate and dopamine, is very good. Thus, this OPPy membrane which can be locally electrodeposited is ideal for the construction of oxidase-based microbiosensors. [Copyright &y& Elsevier]

Abstract: The use of an amperometric biosensor for rapid salicylate determination in blood is described. Photolitography was used to make gold electrodes on a polyester film. The plastic microcell was characterized using cyclic voltammetry to demonstrate the electrochemical performance of the system. The biosensor was constructed by immobilizing salicylate hydroxylase onto the working electrode of the plastic electrochemical microcell. The optimized working conditions were 0.1molL−1 phosphate buffer at pH 7.6 with 0.5mmolL−1 of NADH and 300mV vs. Au as the applied potential. The resulting biosensor exhibited a high sensitivity (97.4nA/mmolL−1 salicylate) and an adequate linear response range (1.2×10−4 to 1.0×10−3 mol −1). The biosensor performance was verified by determining salicylate in spiked blood samples and the results were statistically equivalent to the values obtained from the standard Trinder spectrophotometric method, with a 95% confidence level. This study shows the potential development of a portable, inexpensive and disposable device for point-of-care monitoring. [Copyright &y& Elsevier]

Abstract: A biocomputing system composed of a combination of AND/IDENTITY logic gates based on the concerted operation of three enzymes: lactate oxidase, horseradish peroxidase and glucose dehydrogenase was designed to process biochemical information related to pathophysiological conditions originating from various injuries. Three biochemical markers: lactate, norepinephrine and glucose were applied as input signals to activate the enzyme logic system. Physiologically normal concentrations of the markers were selected as logic 0 values of the input signals, while their abnormally increased concentrations, indicative of various injury conditions were defined as logic 1 input. Biochemical processing of different patterns of the biomarkers resulted in the formation of norepi-quinone and NADH defined as the output signals. Optical and electrochemical means were used to follow the formation of the output signals for eight different combinations of three input signals. The enzymatically processed biochemical information presented in the form of a logic truth table allowed distinguishing the difference between normal physiological conditions, pathophysiological conditions corresponding to traumatic brain injury and hemorrhagic shock, and abnormal situations (not corresponding to injury). The developed system represents a biocomputing logic system applied for the analysis of biomedical conditions related to various injuries. We anticipate that such biochemical logic gates will facilitate decision-making in connection to an integrated therapeutic feedback-loop system and hence will revolutionize the monitoring and treatment of injured civilians and soldiers. [Copyright &y& Elsevier]

Abstract: Nanostructured, hollow spheres of polydiphenylamine (HS-PDPA) are prepared through a “soft template assisted self-assembly” approach. An enzymatic glucose biosensor is fabricated through immobilizing glucose oxidase (GOx) into HS-PDPA matrix. The HS-PDPA–GOx electrode exhibits a pair of well-defined reversible redox peaks with a fast heterogeneous electron transfer rate. At an applied potential of +0.65V, HS-PDPA–GOx electrode possesses high sensitivity (1.77μAmM−1 cm−2), stability and reproducibility towards glucose. The amperometric current response of HS-PDPA–GOx to glucose is linear in the concentration range between 1 and 28mM with a detection limit of 0.05mM (S/N=3). Also, HS-PDPA–GOx electrode shows high selectivity towards glucose in the presence of ascorbic acid, uric acid and acetaminophen at their maximum physiological concentrations. [Copyright &y& Elsevier]

Abstract: The highly sensitive urine glucose meter based on amperometric glucose sensor was developed and commercialized. It shows remarkable performances of wide measurement range in 0–2000mgdl−1, rapid response time as 6s and robustness against influence by interferents like ascorbic acid or acetaminophen. Correlation between the developed urine glucose meter and commercialized clinical-use urine glucose analyzer showed excellent linear relationship. The monitoring of postmeal blood glucose levels by assess of urine glucose of actual subjects was performed with the developed urine glucose meter. The experimental results suggest the urine glucose level 120min following the meal should be the appropriate index for diabetes or impaired glucose tolerance to control blood glucose level. The new portable meter was developed, and is expected for flexible use at places other than home or office. [Copyright &y& Elsevier]

Abstract: In this work the sensitivity-increasing effect of single-walled carbon nanotubes (SWCNTs) in amperometric biosensors, depending on their average length distribution, was studied. For this purpose the SWCNTs were oxidatively shortened and subsequently length separated by size exclusion chromatography. Transmission electron micrographs of different fractions of SWCNTs were collected. Diaphorase “wired” to an osmium redox polymer was blended with the shortened SWCNTs of different lengths. Depending on the average length of the SWCNTs the sensitivity of the amperometric biosensor model system towards oxidation of 1,4-dihydronicotinamide adenine dinucleotide (NADH) was increased by a factor of five. The best performance was achieved with SWCNTs of medium length. The linear range for NADH detection was between 5μM and 7mM, the maximum sensitivity was 47nAμM−1 cm−2, and the detection limit was 1μM. The biosensor exhibited excellent electrocatalytic properties. Even at relatively high NADH concentrations the oxidative current was limited by the diffusion rate of NADH. [Copyright &y& Elsevier]

Abstract: An amperometric bilirubin biosensor was fabricated by complexing the Mn(II) ion with a conducting polymer and the final biosensor surface was coated with a thin polyethyleneimine (PEI) film containing an enzyme, ascorbate oxidase (AsOx). The complexation between poly-5,2′-5′,2″-terthiophene-3-carboxylic acid (PolyTTCA) and Mn(II) through the formation of Mn–O bond was confirmed by XPS. The PolyTTCA–Mn(II) complex was also characterized using cyclic voltammetry. The PolyTTCA–Mn(II)/PEI–AsOx biosensor specifically detect bilirubin through the mediated electron transfer by the Mn(II) ion. To optimize the experimental condition, various experimental parameters such as pH, temperature, and applied potential were examined. A linear calibration plot for bilirubin was obtained between 0.1μM and 50μM with the detection limit of 40±3.8nM. Interferences from other biological compounds, especially ascorbate and dopamine were efficiently minimized by coating the biosensor surface with PEI–AsOx. The bilirubin sensor exhibited good stability and fast response time (<5s). The applicability of this bilirubin sensor was tested in a human serum sample. [Copyright &y& Elsevier]

Abstract: We report on an amperometric biosensor that is based on a nanocomposite of carbon nanotubes (CNT), a nano-thin plasma-polymerized film (PPF), and glucose oxidase (GOx) as an enzyme model. A mixture of the GOx and a CNT film is sandwiched with 10-nm-thick acetonitrile PPFs. Under PPF layer was deposited onto a sputtered gold electrode. To facilitate the electrochemical communication between the CNT layer and GOx, CNT was treated with nitrogen or oxygen plasma. The resulting device showed that the oxidizing current response due to enzymatic reaction was 4–16-fold larger than that with only CNT or PPF, showing that the PPF and/or plasma process is an enzyme-friendly platform for designing electrochemical communication from the reaction center of GOx to the electrode via CNTs. The optimized glucose biosensor showed high sensitivity (sensitivity of 42μAmM−1 cm−2, correlation coefficient of 0.992, linear response range of 0.025–2.2mM, and a detection limit of 6μM at signal/noise ratio of 3, +0.8V versus Ag/AgCl), high selectivity (almost no interference by 0.5mM ascorbic acid) for glucose quantification, and rapid response (<4s to reach 95% of maximum response). Additionally, the devices showed a small and stable background current (0.35±0.013μA) compared with the glucose response (ca. 10μA at 10mM glucose) and suitable reproducibility from sample-to-sample (<3%, n =4). [Copyright &y& Elsevier]

Abstract: In this paper, we present the analytical properties of a new type of polypyrrole-based, enzymatic amperometric biosensor. It is produced by encapsulating the enzyme, glucose oxidase (GOx), into onion-type multilamellar vesicles (MLV). We compare its properties to those of a classical GOx–polypyrrole biosensor. When MLV are used to embed GOx in polypyrrole (PPy), GOx behaves as a Michaelis–Menten enzyme. Without MLV, a deviation to the Michaelis–Menten behaviour is observed for high glucose concentrations. Kinetics parameters of both types of biosensors are studied as a function of the surface charge synthesis: GOx encapsulation induces a 200-fold increase of the apparent maximal current and a 10-fold increase of the apparent Michaelis constant . Sensitivity is improved by a factor of 5. GOx is also shown to be less sensitive to inhibiting ions (Cl−) when MLV are used. A residual amperometric response of 43% instead of 3% is measured. Finally, the long-term stability of biosensors is improved by the GOx encapsulation. All these results are partially explained by our previous study on the morphology of PPy films fabricated with GOx encapsulated into onion-type MLV (). [Copyright &y& Elsevier]

Abstract: A l-lactate-selective microbial biosensor was developed using permeabilized cells of gene-engineered thermotolerant methylotrophic yeast Hansenula polymorpha, over-producing l-lactate:cytochrome c-oxidoreductase (EC 1.1.2.3, flavocytochrome b 2, FC b 2). The construction of FC b 2-producers by over-expression of the gene CYB2 H. polymorpha encoding FC b 2 is described. The HpCYB2 gene under the control of the strong H. polymorpha alcohol oxidase promoter in the frame of a plasmid for multicopy integration was transformed to the recipient strain H. polymorpha C-105 (gcr1 catX) impaired in glucose repression and devoid of catalase activity. The permeabilized cells were either immobilized on the graphite working electrode by physical entrapment of the cell suspension by means of a dialysis membrane or by integration of the cells in an electrochemically generated layer using a cathodic electrodeposition polymer. Phenazine methosulphate was used as a free-diffusing redox mediator. It was assumed that the mediator reacts with mitochondrial FC b 2 after entering the cells in the presence of l-lactate. The biosensor based on recombinant yeast cells exhibited a higher value and hence expanded linear range toward l-lactate as compared to a similar sensor based on the initial cells of H. polymorpha C-105. [Copyright &y& Elsevier]

Abstract: The simple and efficient method for preparing sensitive carbon nanotube/polysulfone/RIgG immunocomposite is described. The membrane of the modified disposable screen-printed electrochemical immunosensor is based on phase inversion method. Carbon nanotube/polysulfone membrane acts both as reservoir of immunological material and transducer while offering high surface area, high toughness and mechanical flexibility. The comparison with graphite/polysulfone/RIgG immunosensors shows a much higher sensitivity for those prepared with carbon nanotubes coupled with polysulfone (PSf). The membrane was characterized by scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), laser profilometer and by atomic force microscopy (AFM). The purity of the materials was evaluated by thermogravimetric analysis (TGA). The roughness value is doubled when MWCNTs are used instead of graphite into the PSf membranes and the incorporation of antibodies enhances the dispersion of the carbon with the polymeric membrane reducing the roughness in all cases. This biosensor was based on the competitive assay between free and labelled anti-RIgG for the available binding sites of immobilized rabbit IgG (RIgG). The RIgG was incorporated into the polysulfone membrane by a phase inversion method. Horse radish peroxidase (HRP) enzyme was used as label and hydroquinone as mediator. The detection limit for competitive assay was determined to be 1.66μg/ml. the linear range of anti-RIgG from 2 to 5μg/ml and the C50 was found at 3.56μg/ml. The sensitivity is five times higher for MWCNT than for graphite electrodes, showing lower unspecific adsorption. [Copyright &y& Elsevier]

Abstract: A novel amperometric ethanol biosensor was constructed using alcohol dehydrogenase (ADH) physically immobilized within poly(vinyl alcohol)–multiwalled carbon nanotube (PVA–MWCNT) composite obtained by a freezing–thawing process. It comprises a MWCNT conduit, a PVA binder, and an ADH function. The measurement of ethanol is based on the signal produced by β-nicotinamide adenine dinucleotide (NADH), the product of the enzymatic reaction. The homogeneity of the resulting biocomposite film was characterized by atomic force microscopy (AFM). The performance of the PVA–MWCNT–ADH biocomposite modified glassy carbon electrode was evaluated using cyclic voltammetry and amperometry in the presence of NADH and in the presence of ethanol. The ethanol content in standard solutions was determined and a sensitivity of 196nAmM−1, a linear range up to 1.5mM, and a response time of about 8s were obtained. These characteristics allowed its application for direct detection of ethanol in alcoholic beverages: beer, red wine, and spirit. [Copyright &y& Elsevier]

Abstract: A novel, nitroreductase (NTR) containing a sequence of six cysteine amino acids, enabling strong thiolate bonds to form on a gold electrode surface without the loss of enzyme activity, was genetically engineered. The enzyme was directly immobilised at a gold electrode without the need for pre-treatment of the surface with a self-assembled monolayer or a conducting polymer. The ensemble was used to develop an amperometric biosensor for the detection of explosives containing nitroaromatic compounds. Preliminary results demonstrate detection levels down to 100 parts per trillion, signifying tremendous promise towards an in situ sensor for the detection of explosives. [Copyright &y& Elsevier]

Abstract: An l-glutamate biosensor modified by cation exchanger membrane on a palladium (Pd) electrode was designed for the purpose of preventing interferences and electrode fouling during the measurement of serum AST and ALT activities. The rate of signal increase obtained by our sensor for the determination of AST and ALT activity was 0.259 and 0.596nA/minU−1 l and the response of the sensor to AST and ALT activity were linear over the range of 8–200 and 8–250Ul−1, respectively. Both AST and ALT activities could be measured sequentially by injecting the serum into a solution containing l-aspartate and α-ketoglutarate. The rate of current increase was relative to AST activity. The activity of ALT was sequentially determined after addition of l-alanine into the solution. The change in the current increase rate after the addition of l-alanine was proportional to the ALT activity. By using the proposed biosensor, the interference of 1mM ascorbic acid was negligible on a dynamical aminotransferase determination when the dynamic data are taken after the steady state of an elevated baseline has been reached. The proposed l-glutamate biosensor provides adequate sensitivity for the measurement of AST and ALT and is expectable to be applied for rapid blood screening of AST and ALT activity in clinical sample. [Copyright &y& Elsevier]

Abstract: Polysulfone membrane is used for the first time for the preparation of electrochemical immunosensors. A disposable immunosensor based on a porous conductor polymer graphite–polysulfone–electrode has been developed using a phase inversion technique for the determination of anti-rabbit IgG (anti-RIgG) as a model analyte. To construct the sensor, a conductor membrane was deposited on the surface of working graphite–epoxy composite (GEC) electrode. The membrane was characterized by SEM. This sensor was based on the competitive assay between free and labeled anti-RIgG for the available binding sites of immobilized rabbit IgG (RIgG). Incubation parameters were optimized in this work. The immunological reaction was detected using an enzymatic-labeling procedure (HRP enzyme) combined with the amperometric detection using H2O2 as substrate and hydroquinone as mediator. This sensor shows stability during a week and a good reproducibility. The current was monitored amperometrically at −0.1V versus SCE and this method showed a linear range of the anti-RIgG from 1 to 6μg/ml. The detection limit was determined to be 0.77μg/ml. [Copyright &y& Elsevier]

Abstract: The co-immobilization of glucose oxidase (GOD) and hexokinase/glucose-6-phosphate dehydrogenase (HEX) in the silica hybrid sol–gel film for development of amperometric biosensors was investigated. The silica hybrid film fabricated by hydrolysis of the mixture of tetraethyl orthosilicate and 3-(trimethoxysiyl)propyl methacrylate possessed a three-dimension vesicle structure and good uniformity and conformability, and was ready for enzyme immobilization. The electrochemical and spectroscopic measurements showed that the silica hybrid sol–gel provided excellent matrice for the enzyme immobilization and that the immobilized enzyme retained its bioactivity effectively. The immobilized GOD could catalyze the oxidation of glucose, which could be used to determine glucose at +1.0V without help of any mediator. The competition between GOD and HEX for the substrate glucose involving ATP as a co-substrate led to a decrease of the glucose response, which allowed us to develop an ATP sensor with a good stability. The fabricated silica hybrid sol–gel matrice offered a stage for further study of immobilization and electrochemistry of proteins. [Copyright &y& Elsevier]

Abstract: A novel method has been developed to immobilize tyrosinase onto the surface of boron-doped diamond (BDD) electrode. The hydrogen-terminated BDD (HBDD) surface was first functionalized by photochemically linking vinyl groups of allylamine, producing covalently linked amine-terminated active BDD (ABDD) surface. Then the tyrosinase was immobilized onto the ABDD surface by carbodiimide coupling reaction. The amperometric response was measured as a function of concentration of phenolic compounds in 0.1M phosphate buffer solution (pH 6.5). The tyrosinase-modified ABDD electrode gave a linear response range of 1–175, 1–200 and 1–200μM and sensitivity of 80.0, 181.4 and 110.0mAM−1 cm−2 for phenol, p-cresol, 4-chlorophenol, respectively. Moreover, selective detection of dopamine (DA) in the presence of ascorbic acid (AA) has been demonstrated with the tyrosinase-modified ABDD electrode. Linearity was observed within the range of 5–120μM. The above enzyme electrode could maintain 90% of its original activity after intermittent use for 1 month when storing in a dry state at 4°C. [Copyright &y& Elsevier]

Abstract: The structure and biosensor characteristics of complex between glucose oxidase (GOD) and plasma-polymerized nanothin film (PPF), in which the thickness is several nanometers, were investigated by atomic force microscopy (AFM) and electrochemical measurement. The GOD molecules were densely adsorbed onto the PPF surface treated by nitrogen plasma and the individual GOD molecules were observed. Subsequently, the GOD densely packed array on the PPF surface was subsequently treated by plasma polymerization (overcoating). AFM image showed that the thicker film gave the smoother surface, indicating that the GOD adsorbed on the surface was embedded more deeply in PPF. The amperometric biosensor characteristics of the GOD–PPF complex on a platinum electrode showed the current increment due to the enzymatic reaction with glucose addition, indicating that enzyme activity was retained although the enzyme has been exposed to the plasma gas related to diffusion of the substrate. This means that under mild exposure to organic plasma, the enzyme does not become seriously dysfunctional. Amperometric biosensor characteristics were strongly affected by monomer and thickness of PPF overcoating related with the diffusion of the substrate (glucose). Considering that the film deposition was performed using microfabrication-compatible organic plasma, our new method for protein architecture has a great potential of enabling high throughput production of bioelectronic devices. [Copyright &y& Elsevier]

Abstract: The level of uric acid (UA) has a high relationship with gout, hyperuricemia and Lesch-Nyan syndrome. The determination of UA is an important indicator for clinics and diagnoses of kidney failure. An amperometric UA biosensor based on an Ir-modified carbon (Ir–C) working electrode with immobilizing uricase (EC 1.7.3.3) was developed by thick film screen printing technique. This is the first time to report the utilization of an uricase/Ir–C electrode for the determination of UA by using chronoamperometric (CA) method. The high selectivity of UA biosensor was achieved due to the reduction of H2O2 oxidation potential based on Ir–C electrode. Using uricase/Ir–C as the sensing electrode, the interference from the electroactive biological species, such as ascorbic acid (AA) and UA (might be directly oxidized on the sensing electrode) was slight at the sensing potential of 0.25V (versus Ag/AgCl). UA was detected amperometrically based on uricase/Ir–C electrode with a sensitivity of 16.60μAmM−1 over the concentration range of 0.1–0.8mMUA, which was within the normal range in blood. The detection limit of UA biosensor was 0.01mM (S/N=6.18) in pH 7 phosphate buffer solution (PBS) at 37°C. The effects of pH, temperature, and enzymatic loading on the sensing characteristics of the UA biosensor were also investigated in this study. [Copyright &y& Elsevier]

Abstract: An amperometric enzyme sensor using tyrosinase (PPO) entrapped in polyacrylamide microgels has been developed for determination of phenolic compounds. Polyacrylamide microgels were obtained by the concentrated emulsion polymerization method. The crosslinking of the polymer matrix optimum to retain the enzyme and to allow the diffusion of the compounds involved in the enzyme reaction has been studied (4.0%) as well as the influence on the response of analytical parameters such as pH, temperature, enzyme load and working potential. The useful lifetime of the biosensor was 27 days and it was useful to determine monophenolics compounds (e.g. cresol, chlorophenol) and diphenolics compounds (e.g. catechol and dopamine) by amperometric measurements at −100mV (versus SCE) in a batch system. The results showed that the substrate structures have a great influence on the sensor response. [Copyright &y& Elsevier]

Abstract: A glucose amperometric biosensor based on the immobilization of glucose oxidase (GOx) in microparticles prepared by polymerization of the ionic liquid 1-vinyl-3-ethyl-imidazolium bromide (ViEtIm+Br−) using the concentrated emulsion polymerization method has been developed. The polymerization of the emulsion dispersed phase, in which the enzyme was dissolved together with the ionic liquid monomer, provides poly(ViEtIm+Br−) microparticles with entrapped GOx. An anion-exchange reaction was carried out for synthesizing new microparticles of poly(ViEtIm+(CF3SO2)2N−) and poly(ViEtIm+BF4 −). The enzyme immobilization method was optimized for biosensor applications and the following optimal values were determined: pH 4.0 for the synthesis medium, 1.23M monomer concentration and 3.2% (w/w) cross-linking content. The performance of the biosensor as a function of some analytical parameters such as pH and temperature of the measuring medium, and enzymatic load of the microparticles was also investigated. The effect of the substances which are present in serum samples such as uric and ascorbic acid was eliminated by using a thin Nafion layer covering the electrode surface. The biosensor thus prepared can be employed in aqueous and in non-aqueous media with satisfactory results for glucose determination in human serum samples. The useful lifetime of this biosensor was 150 days. [Copyright &y& Elsevier]

Abstract: An amperometric flow biosensor, using laccase from Rigidoporus lignosus as bioelement was developed. The laccase was kinetically characterized towards various phenolics both in solution and immobilized to a hydrophilic matrix by carbodiimide chemistry. A bioreactor connected to an amperometric flow cell by a FIA system was filled with the immobilized enzyme and the operational conditions of this biosensor were optimized as regards pH. Under the adopted experimental conditions, the immobilized enzyme oxidizes all the substrate molecules avoiding the need of cumbersome calibration procedures. The biosensor sensitivity, which was found to be 100nA/μM for some of the tested substrates, resulted to be constant for more than 100 working days. This biosensor permits the detection of phenolics in aqueous solutions at concentrations in the nanomolar range and was successfully used to detect phenolics in wastewaters from olive oil mill without sample preparation. [Copyright &y& Elsevier]

Abstract: A novel hydrogen peroxide biosensor was fabricated by using a DNA–Cu(II) complex as a novel electrocatalyst for the reduction of hydrogen peroxide (H2O2). A polyion complex (PIC) membrane composed of DNA and poly(allylamine) (PAA) functioned as a support matrix for immobilization of electrocatalytic element-copper ion. The circular dichroism (CD) spectrum of the DNA–Cu(II)/PAA membrane in wet state showed that the DNA exists in B-like form within the membrane. Electrochemical measurements of the DNA–Cu(II)/PAA membrane-modified glassy carbon (GC) electrode revealed that the copper ion embedded in the DNA/PAA layer exhibits good electrochemical behaviors, and the electrochemical rate constant between the immobilized copper ion and the GC electrode surface was estimated to be 26.4s−1. The resulting DNA–Cu(II)/PAA/GC electrode showed an excellent electrocatalytic activity for the H2O2 reduction. The sensitivity of the sensor for the determination of H2O2 was affected by the amount of each component, such as copper ion, DNA and PAA in the DNA–Cu(II)/PAA membrane. Effects of applied potential, pH, temperature, ionic strength and buffer concentrations upon the response currents of the sensor were also investigated for an optimum analytical performance. Even in the presence of dissolved oxygen, the sensor exhibited highly sensitive and rapid (response time, less than 5s) response to H2O2. The steady-state cathodic current responses of the sensor obtained at −0.2V versus Ag/AgCl in air-saturated 50mM phosphate buffer (pH 5.0) increased linearly up to 135μM with the detection limit of 50nM. Interference by ascorbic acid and uric acid due to the reduction of Cu(II) was effectively cancelled by further modification of outermost layer of polyion complex film. In addition, the sensor exhibited good reproducibility and stability. [Copyright &y& Elsevier]

Abstract: A molecular assembly consisting of a redox enzyme, NADH peroxidase, a metallized double-helical peptide, and a gold nanoparticle immobilized onto a gold wire derivatized with a benzenedithiol compound, initiated and conducted redox signals in the presence of H2O2 and NADH. The current generated by the binding of NADH, the electron donor, was transduced through the molecular assembly with apparently little loss of signal to the solution. The currents measured correlate to an electron transfer rate constant on the order of 3000s−1 within each assembly. This electron transfer rate is two orders of magnitude higher than the endogenous electron transfer rate from NADH to the native enzyme, 27s−1. This rate indicates that the metallized peptide is in a conformation conducive for electron transfer and, in conjunction with the redox enzyme, can form effective conduits of electrical signals. This work demonstrates the feasibility of utilizing designed and highly efficient biomolecular assemblies for the production of ultra-sensitive, in-situ biosensors. [Copyright &y& Elsevier]

Abstract: The amperometric detection of neurotransmitters metabolite of 3,4-dihydroxyphenylacetic acid (DOPAC) was achieved at a tyrosinase–chitosan composite film-modified glassy carbon (GC) electrode. The optimal conditions for the preparation of the biosensor were established. This bio-composite film was characterized by scanning electron microscopy (SEM) and Fourier transformed infrared (FT-IR) spectra, suggesting that chitosan covalently connected to chitosan chains. Electrochemical characterization of the bio-hybrid membrane-covered electrodes were also performed in 0.05M phosphate buffer solution (pH 6.52) containing neurotransmitters or their derivatives by using cyclic voltammetry (CV), linear sweep voltammetry (LSV), square wave voltammetry (SWV) and amperometry. This simply-prepared protein–polysaccharide hybrid film provides a microenvironment friendly for enzyme loading. The sensor was operated at −0.15V with a short response time. The current linearly increased with the increasing concentration of DOPAC over the concentration of 6nM–0.2mM. The lower detection limit for DOPAC is 3nM (S/N=3). The sensitivity of the sensor is 40μAmM−1. A physiological level of neurotransmitters and their derivatives including dopamine, l-dopa, adrenaline, noradrenaline and homovanillic acid as well as ascorbic acid, uric acid and acetaminophen do not affect the determination of DOPAC. [Copyright &y& Elsevier]