A new approach for nitrite determination based on a HRP/catalase biosensor

In this paper, a new concept of enzyme inhibition-based biosensor involving a two enzyme system was developed. The latter displays a signal increase instead of a decrease in the presence of an inhibitor. HRP and catalase were thus separately entrapped into Layered Double Hydroxides (LDH), an anionic clay, as a host matrix. The inner layer was constituted of HRP electrically wired by [Zn₂CrABTS] LDH and the outer layer contained catalase immobilized in [Zn₃AlCl] LDH. Both enzymes catalyzed the decomposition of H₂O₂, HRP its reduction and catalase its breakdown into oxygen and water. Nitrite was selected as a specific inhibitor of catalase. In the presence of H₂O₂, the nitrite addition blocked the H₂O₂ consumption by catalase, inducing thus an increase in the amperometric signal of the H₂O₂ reduction at 0 V by the wired HRP. The optimum configuration of the bi-enzyme biosensor displayed in aerated aqueous solutions, a nitrite sensitivity of 102 μA M^− 1· cm^− 2 with a fast response time, the detective limit being 4 μM.     

Preparation and electrochemical application of a new biosensor based on plant tissue/polypyrrole for determination of acetaminophen

Banana tissue containing polyphenol oxidase was incorporated into polypyrrole matrix to make a biosensor for the analysis of acetaminophen (ACT). The electrocatalytic behaviour of oxidized acetaminophen was studied at the surface of the biosensor, using various electrochemical methods. The advantages of this biosensor for the determination of acetaminophen are excellent catalytic activity, good detection limit and high exchange current density. The electrochemical and structural properties of the electrode were assessed using cyclic voltammetry, differential voltammetry, chronoamperometric techniques. The analytical properties (sensitivity, I _p ) of this biosensor increased with plant tissue loading. Also this new biosensor was successfully applied for determination of acetaminophen in biologic samples.     

An electrochemical sensing platform based on a new copper complex for the determination of hydrogen peroxide and nitrite

Abstract

A new copper(II) complex [Cu(C₁₂H₂₃N₃)₄Br₂·2H₂O] was synthesized and its structure was characterized by x-ray crystallography and elemental analysis. The copper atom had a distorted octahedron coordination involving two bromide anions and four nitrogen atoms from the 1-decyl-1H-[1,2,4]triazole ligands. Moreover, the electrochemical behavior and electrocatalysis of the carbon paste electrode (Cu-CPE) bulk-modified by the complex have been studied in detail. The Cu-CPE showed excellent electrocatalytic activities toward the reduction of hydrogen peroxide and nitrite, and the detection limit was much lower than that mentioned in earlier reports. This bulk-modified CPE has good reproducibility, long-term stability and surface renewability, which appear promising for constructing chemical sensors.     

A biosensor array based on polyaniline

This paper describes the fabrication of polyaniline-based microsensors and microsensor arrays for the estimation of glucose, urea, and triglycerides. Microelectronics technology has been used to produce gold interdigitated microelectrodes on oxidized silicon wafers. Polymer deposition and enzyme immobilization has been done electrochemically. Electrochemical potential control has been used to direct enzyme immobilization to the chosen microelectrodes and prevent it at other microelectrodes in contact with the enzyme solution. This has enabled the immobilization of three different enzymes on three closely spaced microelectrodes, resulting in a sensor array which can analyze a sample containing a mixture of glucose, urea, and triolein in a single measurement using a few microliters of the sample. This strategy is quite general and can be extended to other enzyme-substrate systems to eventually produce an "electronic tongue".     

Development of trypsin biosensor based on ion sensitive field-effect transistors for proteins determination

This new biosensor for protein determination is based on a possibility of translation of either a proton or hydroxyl ion arising during protein hydrolysis in the presence of trypsin by means of ion selective field effect transistor (ISFET). The conditions of trypsin immobilization and main biosensor characteristics were optimized using hydrolysis reaction of nalpha-benzoyl-l-arginine ethyl ester hydrochloride (BAEE). The trypsin was immobilized on the ISFET surface using a co-reticulation process between the enzyme and BSA (4% trypsin, 6% BSA) in saturated glutaraldehyde vapour. The limit of detection of BAEE with this biosensor is 0.5 mM with a linear dynamics range from 0.5 to 5 mM, and sensitivity is about 6 mV/mM. The time of biosensor response was 5–7 min.The possibility of the application of developed biosensor for detection of small penta-peptide, which is used in some cosmetic products, has been demonstrated.     

Conductometric biosensor based on glucose oxidase and beta-galactosidase for specific lactose determination in milk

This paper investigates the development of a biosensor associating two distinct enzymatic activities, that of the beta-galactosidase and that of the glucose oxidase, in order to apply it for the quantitative detection of lactose in milk. To eliminate interferences with glucose, a differential mode of measurement was used. Results show a linear calibration curve for lactose concentration between 60 and 800 μM (0.03 to 0.3 g/L). Tests with real commercial milk samples were carried out to validate the conductometric biosensor.     

Complexing of heavy metals with DNA and new bioaffinity method of their determination based on amperometric DNA-based biosensor

The immobilized single-stranded DNA (ssIDNA) has been found to be a very effective biospecific analytical reagent when used in a newly developed bioaffinity method of the determination of heavy metals based on the amperometric DNA-based biosensor. This has been concluded from the comparative study of the complexing of heavy metals with double-stranded DNA, single-stranded DNA, and ssIDNA, using Fe(III) and Cu(II) as a model (metal/nucleotide ratio and stability constants are maximum for ssIDNA), from the study of adsorption of Fe(III), Cu(II), Pb(II), and Cd(II) on nitrocellulose membranes, containing single-stranded DNA, and from the determination of their binding constants with ssIDNA. According to these data, the chosen heavy metals can be lined up in a series of binding strengths with ssIDNA: Cu(II) > Pb(II) > Fe(III) > Cd(II). The method of the determination of heavy metals is based on biospecific preconcentration of metal ions on the biosensor followed by the destruction of DNA-metal complexes with ethylenediaminetetraacetate and voltammogram recording has been proposed. The lower detection limits are 4.0 x 10(-11), 1.0 x 10(-10), 1.0 x 10(-9), and 5.0 x 10(-9) M for Cu(II), Pb(II), Cd(II), and Fe(III), respectively. The heavy metals have been assayed in multicomponent environmental and biological systems such as natural and drinking water, milk, and blood serum samples.     

A novel urea biosensor based on zirconia

Electrochemically deposited biocompatible zirconia (ZrO₂) film on gold coated glass electrodes has been utilized for the fabrication of urea biosensor. The prepared ZrO₂ films and bioelectrodes have been characterized using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and electrochemical techniques, respectively. The urea biosensor, fabricated by immobilizing mixed enzyme [urease (Urs) and glutamate dehydrogenase (GLDH)] on this nanobiomaterial, shows linearity up to 40 mg dL^− 1 of analyte (urea) and sensitivity of 0.071 μA/(mM cm^− 2) with stability up to 4 months when stored at 4 °C. The low value of Michaelis-Menten constant (K_m) estimated using Hans plot as 0.5 mM indicates enhancement in the affinity and/or activity of enzyme attached to this nanostructured biocompatible matrix.     

Disposable biosensor based on a hemoglobin colloidal gold-modified screen-printed electrode for determination of hydrogen peroxide

A disposable reagentless hydrogen peroxide biosensor based on the direct electrochemistry of hemoglobin immobilized on a colloidal gold-modified screen-printed carbon electrode (Hb-Au-SPCE) was proposed. The electrochemical behavior of immobilized Hb at a SPCE was studied for the first time. The electrode reaction of immobilized Hb showed a surface-controlled process with an electron transfer rate constant of (0.40 /spl plusmn/ 0.02) s/sup -1/ determined in the scan rate range from 25 to 200 mV s/sup -1/. The Hb-Au-SPCE exhibited an electrocatalytic activity toward the reduction of hydrogen peroxide with a K/sub M//sup app/ value of 1.8 mM, which was allowed to be used as a disposable sensor for determination of hydrogen peroxide with a linear range from 1.0 /spl times/ 10/sup -5/ M to 3.2 /spl times/ 10/sup -4/ M, a detection limit of 5.5 /spl times/ 10/sup -6/ M at 3/spl sigma/, a high sensitivity, fast response, and good selectivity, accuracy, and reproducibility. The disposable reagentless sensor was stable, low cost, and simple to use for detection of hydrogen peroxide in real samples.     

Hybrid biosensor for the determination of lactose

Genetically manipulated bacteria Escherichia coli K-12 recombinant PQ-37 and glucose oxidase (EC 1.1.3.4) were used for the construction of a hybrid lactose sensor because of the hyperproduction of beta-galactosidase (EC 3.2.1.23) by E. coli effected by a genotoxic agent. The biocatalytic layer was prepared by coimmobilization of the E. coli cells with glucose oxidase on the nylon network via glutardialdehyde and fixed to the Clark oxygen electrode. The influence of pH, temperature, and concentration of activators of beta-galactosidase on the sensor response was tested. Analyses of milk products were completed without any special pretreatment of the samples. The contents of lactose determined by hybrid sensor agree with conventional photometric measurements. Standard relative deviation is less than 3% for all samples. The half-life of operational stability is 30 days.     

Prototype amperometric biosensor for sialic acid determination

This paper describes the first report on the development, characterization, and applications of a prototype amperometric biosensor for free sialic acid (SA). The sensor was constructed by the coimmobilization of two enzymes, i.e., N-acetylneuraminic acid aldolase and pyruvate oxidase, on a polyester microporous membrane, which was then mounted on top of a platinum disk electrode. The SA biosensor operation was based on the sequential action of the two enzymes to ultimately produce hydrogen peroxide, which was then detected by anodic amperometry at the platinum electrode. The surface of the platinum electrode was coated with an electropolymeric layer to enhance the biosensor selectivity in the presence of interfering oxidizable species. Optimization of the enzyme layer composition resulted in a fast and steady current response in phosphate buffer pH 7.2 at 37 degrees C. The limit of detection was 10 microM, and the response was linear to 3.5 mM (r = 0.9987). The prepared SA biosensors retained approximately 85% of their initial sensitivity after 8 days and showed excellent response reproducibility (CV = 2.3%). Utilization of a third enzyme, sialidase, expanded the scope of the present SA biosensor to determine bound sialic acid as well. The merits of the described biosensor allowed its successful application in determining SA in biological and pharmaceutical samples. The obtained results indicated that the presented SA biosensor should be a useful bioanalytical tool in several biological and clinical applications such as screening of SA as a nonspecific tumor marker as well as monitoring of tumor therapy.     

A nitrite sensor based on a highly sensitive nitrite reductase mediator-coupled amperometric detection

Highly sensitive nitrite sensors have been developed for the first time based on mediator-modified electrodes. Tetraheme cytochrome c nitrite reductase from Sulfurospirillum deleyianum and cytochrome cd(1) nitrite reductase from Paracoccus denitrificans are able to accept electrons from artificial electron donors, which simultaneously act as electron mediators between the enzyme and an amperometric electrode. In addition to methyl viologen, redox-active compounds such as phenazines (phenosafranin, safranin T, N-methylphenazinium, 1-methoxy-N-methylphenazinium) and triarylmethane redox dyes (bromphenol blue and red) were selected from a range of redox compounds exhibiting the most efficient performance for nitrite detection. After precipitation, the electron mediators were incorporated in a graphite electrode material. Enzyme immobilization is performed by entrapment in a poly(carbamoyl sulfonate) (PCS) hydrogel. Diffusion coefficients and apparent heterogeneous rate constants of the mediators as well as homogeneous rate constants of nitrite sensors were determined by chronoamperometry and cyclic voltammetry. The phenosafranin-modified electrode layered with the PCS hydrogel immobilization of tetraheme cytochrome c nitrite reductase yielded linear current responses up to 250 μM nitrite with a sensitivity of 446.5 mA M(-)(1) cm(-)(2). The detection limit of the enzymatic nitrite sensor was found to be 1 μM nitrite.     

A reduced graphene oxide based electrochemical biosensor for tyrosine detection

In this paper, a 'green' and safe hydrothermal method has been used to reduce graphene oxide and produce hemin modified graphene nanosheet (HGN) based electrochemical biosensors for the determination of l-tyrosine levels. The as-fabricated HGN biosensors were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FTIR) spectra and thermogravimetric analysis (TGA). The experimental results indicated that hemin was successfully immobilized on the reduced graphene oxide nanosheet (rGO) through π-π interaction. TEM images and EDX results further confirmed the attachment of hemin on the rGO nanosheet. Cyclic voltammetry tests were carried out for the bare glass carbon electrode (GCE), the rGO electrode (rGO/GCE), and the hemin-rGO electrode (HGN/GCE). The HGN/GCE based biosensor exhibits a tyrosine detection linear range from 5?×?10(-7)?M to 2?×?10(-5)?M with a detection limitation of 7.5?×?10(-8)?M at a signal-to-noise ratio of 3. The sensitivity of this biosensor is 133 times higher than that of the bare GCE. In comparison with other works, electroactive biosensors are easily fabricated, easily controlled and cost-effective. Moreover, the hemin-rGO based biosensors demonstrate higher stability, a broader detection linear range and better detection sensitivity. Study of the oxidation scheme reveals that the rGO enhances the electron transfer between the electrode and the hemin, and the existence of hemin groups effectively electrocatalyzes the oxidation of tyrosine. This study contributes to a widespread clinical application of nanomaterial based biosensor devices with a broader detection linear range, improved stability, enhanced sensitivity and reduced costs.     

Fabrication of Neisseria gonorrhoeae biosensor based on chitosan-MWCNT platform

We report results of studies relating to preparation and characterization of DNA electrodes based on the chitosan-MWCNT/ITO nanobiocomposite platform for electrochemical detection of gonorrhoea, the most common bacterial sexually transmitted disease. (STD). This biosensing electrode has been characterized using FT-IR, SEM, cyclic voltammetry and differential pulse voltammetry, etc. The sensing characteristics have been investigated in phosphate buffer saline using methylene blue as the hybridization indicator. This DNA biosensor has a response time of 60 s and is found to be stable for about 4 months when stored at 4 °C. The results of DPV studies reveal that this bioelectrode can detect complementary DNA concentration in a wide range of 1 × 10^− 6 M to 1 × 10^− 17 M with a detection limit of 1 × 10^− 16 M.     

A new assay for endonuclease/methyltransferase activities based on graphene oxide

A new endonuclease/methyltransferase activity assay method based on graphene oxide (GO) is developed. Substrate DNA is designed to possess a double-stranded part to serve as a nuclease substrate and a single-stranded part for anchoring the DNA to the GO surface via strong noncovalent binding. Nuclease-mediated DNA hydrolysis induces the recovery of fluorescence intensity of the dye attached to the end of the double-stranded DNA region. This GO-based method allows real-time measurement and quantitative assay for endonuclease/methyltransferase activities in short time.     

Glucose biosensor based on the microcantilever

Diagnosis and management of diabetes require quantitative and selective detection of blood glucose levels. We report a technique for micromechanical detection of biologically relevant glucose concentrations by immobilization of glucose oxidase (GOx) onto a microcantilever surface. Microfabricated cantilevers have traditionally found utility in atomic force microscope imaging. During the past decade, however, microcantilevers have been increasingly used as transducers in chemical-sensing systems. This paper describes the combination of this technology with enzyme specificity to construct a highly selective glucose biosensor. The enzyme-functionalized microcantilever undergoes bending due to a change in surface stress induced by the reaction between glucose in solution and the GOx immobilized on the cantilever surface. Experiments were carried out under flow conditions. The common interferences for glucose detection in other detection schemes have been tested and have shown to have no effect on the measurement of blood glucose level by this technique.     

A mediator-free self-powered glucose biosensor based on a hybrid glucose/MnO2 enzymatic biofuel cell

Self-powered glucose biosensor(SPGB)is of great interest due to the advantages including single configuration,good stability and particularly no need of external power sources.Herein,a mediator-free SPGB with high sensitivity and good selectivity is constructed based on a hybrid enzymatic biofuel cell(EBFC)composed of a glucose oxidase/cobalt phthalocyanine/1-pyrenebutyric acid/buckypaper(GOD/CoPc/PBA/BP)bioanode and a MnO₂/PBA/BP capacitive cathode.The efficient electron transfer from GOD to electrodes is achieved successfully through the anode oxidation of hydrogen peroxide(H₂O₂),one nature product of glucose oxidation catalyzed by GOD,thus avoiding the potential drawbacks posed by the use of redox mediators.CoPc servers as an efficient catalyst to lower the anode potential required by the reaction of H₂O₂ to 0.17 V.The MnO₂/PBA/BP capacitive cathode is utilized because it can not only provide a high discharge potential and adequate capacitance to match the bioanode well,but also exhibit no potential interference to the anodic reaction.The concentration of glucose can be detected simply by measuring the output of the SPGB and a wide linear detection range from 0.5 to 8 mM has been obtained with high sensitivities of 48.66 and 32.12μA·cm^?2·mM^?1 with and without stirring,respectively.The recoveries of glucose in grape juice and human serum are in the range from 99.5%to 101.2%with the relative standard deviation(RSD)less than 8%,indicating the good promise of the SPGB in sensing glucose in real samples.     

Amperometric nitrate biosensor based on Carbon nanotube/Polypyrrole/Nitrate reductase biofilm electrode

This study describes the construction and characterization of an amperometric nitrate biosensor based on the Polypyrrole (PPy)/Carbon nanotubes (CNTs) film. Nitrate reductase (NR) was both entrapped into the growing PPy film and chemically immobilized via the carboxyl groups of CNTs to the CNT/PPy film electrode. The optimum amperometric response for nitrate was obtained in 0.1 M phosphate buffer solution (PBS), pH 7.5 including 0.1 M lithium chloride and 7 mM potassium ferricyanide with an applied potential of 0.13 V (vs. Ag/AgCl, 3 M NaCl). Sensitivity was found to be 300 nA/mM in a linear range of 0.44-1.45 mM with a regression coefficient of 0.97. The biosensor response showed a higher linear range in comparison to standard nitrate analysis methods which were tested in this study and NADH based nitrate biosensors. A minimum detectable concentration of 0.17 mM (S/N = 3) with a relative standard deviation (RSD) of 5.4% (n = 7) was obtained for the biosensor. Phenol and glucose inhibit the electrochemical reaction strictly at a concentration of 1 μg/L and 20 mg/L, respectively. The biosensor response retained 70% of its initial response over 10 day usage period when used everyday.