Highly sensitive determination of hydrogen peroxide and peroxidase with tetrathiafulvalene-based electrodes and the application in immunosensing

Advances in biotechnological synthetic applications of carbon nanostructured systems

In the last few years carbon nanostructures have been applied for the immobilization of enzymes and biomimetic organo-metallic species useful for biotechnological applications. The nature of the support and the method of immobilization are responsible for the stability, reactivity and selectivity of the system. In this review, we focus on the recent advances in the use of carbon nanostructures, carbon nanotubes, carbon nanorods, fullerene and graphene for the preparation of biocatalytic and biomimetic systems and for their application in the development of green chemical processes.

A novel protocol for covalent immobilization of thionine on glassy carbon electrode and its application in hydrogen peroxide biosensor

A novel protocol for effectively covalent immobilization of thionine (Th) was proposed, which was based on Schiff-base reaction between -NH(2) of Th and -COH which was in situ generated on glassy carbon electrode (GCE) via simple potentiostatic activation in diluted nitric acid. GCE pretreated by potentiostatic activation possessed CHO-riched surface and microporous structure with high distribution density of electron transfer sites, and thus it became a good candidate for effective immobilization of Th through imine bond with high stability. The application of the resulting Th modified electrode in hydrogen peroxide biosensor was also investigated and it exhibited rapid response to H(2)O(2) within 3s. The linear calibration ranged from 5.0x10(-7) to 5.8x10(-3)M with a detection limit of 1.0x10(-7)M. The effective immobilization of Th on potentiostatically activated GCE surface has deep significance in mediator immobilization, on which further researches based are under way.

Point-of-care testing of proteins

Point-of-care testing (POCT) is a fast developing area in clinical diagnostics that is considered to be one of the main driving forces for the future in vitro diagnostic market. POCT means decentralized testing at the site of patient care. The most important POCT devices are handheld blood glucose sensors. In some of these sensors, after the application of less than 1 microl whole blood, the results are displayed in less than 10 s. For protein determination, the most commonly used devices are based on lateral flow technology. Although these devices are convenient to use, the results are often only qualitative or semiquantitative. The review will illuminate some of the current methods employed in POCT for proteins and will discuss the outlook for techniques (e.g., electrochemical immunosensors) that could have a great impact on future POCT of proteins.

A mediatorless and label-free amperometric immunosensor for detection of h-IgG

A novel experimental methodology for studying a mediatorless and label-free immunosensor is proposed by immobilizing antibody on gold nanoparticle/L-cysteine coated electrode (nano-Au/L-cysteine electrode). Differential pulse voltammograms (DPV) resulting from the assembled immunosensor indicate that the immunosensor shows excellent electrochemical response to dopamine so that the electrochemical response is utilized for the signal generation step of the immunosensor. Therefore, by means of unenzymatic-labeling procedure combined with the amperometric detection using dopamine as substrate, the immunological reaction can be detected. After the immunosensor is incubated with h-IgG solution, the access of electrocatalytic behavior center of the immunosensor to dopamine is partly inhibited, which leads to a linear decrease in amperometric response of the immunosensor with h-IgG concentration over a range 0.82-90 ng mL(-1) by DPV.

Electrochemical biochips for protein analysis

Proteins bear important functions for most life processes. It is estimated that the human proteome comprises more than 250,000 proteins. Over the last years, highly sophisticated and powerful instruments have been developed that allow their detection and characterization with great precision and sensitivity. However, these instruments need well-equipped laboratories and a well-trained staff. For the determination of proteins in a hospital, in a doctor's office, or at home, low-budget protein analysis methods are needed that are easy to perform. In addition, for a proteomic approach, highly parallel measurements with small sample sizes are required. Biochips are considered as promising tools for such applications. The following chapter describes electrochemical biochips for protein analysis that use antibodies or aptamers as recognition elements.

Amperometric third-generation hydrogen peroxide biosensor based on the immobilization of hemoglobin on multiwall carbon nanotubes and gold colloidal nanoparticles

A convenient and effective strategy for preparation nanohybrid film of multi-wall carbon nanotubes (MWNT) and gold colloidal nanoparticles (GNPs) by using proteins as linker is proposed. In such a strategy, hemoglobin (Hb) was selected as model protein to fabricate third-generation H2O2 biosensor based on MWNT and GNPs. Acid-pretreated, negatively charged MWNT was first modified on the surface of glassy carbon (GC) electrode, then, positively charged Hb was adsorbed onto MWNT films by electrostatic interaction. The {Hb/GNPs}n multilayer films were finally assembled onto Hb/MWNT film through layer-by-layer assembly technique. The assembly of Hb and GNPs was characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM). The direct electron transfer of Hb is observed on Hb/GNPs/Hb/MWNT/GC electrode, which exhibits excellent electrocatalytic activity for the reduction of H2O2 to construct a third-generation mediator-free H2O2 biosensor. As compared to those H2O2 biosensors only based on carbon nanotubes, the proposed biosensor modified with MWNT and GNPs displays a broader linear range and a lower detection limit for H2O2 determination. The linear range is from 2.1x10(-7) to 3.0x10(-3) M with a detection limit of 8.0x10(-8) M at 3sigma. The Michaelies-Menten constant KMapp value is estimated to be 0.26 mM. Moreover, this biosensor displays rapid response to H2O2 and possesses good stability and reproducibility.

Construction of amperometric immunosensors based on the electrogeneration of a permeable biotinylated polypyrrole film

The construction of amperometric immunosensors to cholera antitoxin immunoglobulins were shown to have improved sensitivity when the cholera toxin B subunit biorecognition entity was linked to an electrogenerated biotinylated polypyrrole film copolymerized with pyrrole-lactobionamide monomer. The copolymer exhibits greater film permeability than biotinylated polypyrrolic or polyphenolic films for the permeation of electroactive species. Hence, when the presence of the HRP marker of the immunoassay was determined using hydroquinone, the production of electroactive quinone was shown to permeate faster to the electrode, thus providing a faster response time.

Disposable amperometric immunosensor system for rabbit IgG using a conducting polymer modified screen-printed electrode

A disposable and mediatorless immunosensor based on a conducting polymer (5,2':5'2"-terthiophene-3'-carboxylic acid) coated screen-printed carbon electrode has been developed using a separation-free homogeneous technique for the detection of rabbit IgG as a model analyte. Horseradish peroxidase (HRP) and streptavidin were covalently bonded with the polymer on the electrode and biotinylated antibody was immobilized on the electrode surface using avidin-biotin coupling. This sensor was based on the competitive assay between free and labeled antigen for the available binding sites of antibody. Glucose oxidase was used as a label and in the presence of glucose, H(2)O(2) formed by the analyte-enzyme conjugate was reduced by the enzyme channeling via HRP bonded on the electrode. The catalytic current was monitored amperometrically at -0.35 V vs. Ag/AgCl and this method showed a linear range of RIgG concentrations from 0.5 to 2 microg/ml with standard deviation +/-0.0145 (n=4). Detection limit was determined to be 0.33 microg/ml.

Mediatorless biosensor for H(2)O(2) based on recombinant forms of horseradish peroxidase directly adsorbed on polycrystalline gold

Four forms of horseradish peroxidase (HRP) have been used to prepare peroxidase-modified gold electrodes for mediatorless detection of peroxide: native HRP, wild type recombinant HRP, and two recombinant forms containing six-His tag at the C-terminus and at the N-terminus, respectively. The adsorption of the enzyme molecules on gold was studied by direct mass measurements with electrochemical quartz crystal microbalance. All the forms of HRP formed a monolayer coverage of the enzyme on the gold surface. However, only gold electrodes with adsorbed recombinant HRP forms exhibited high and stable current response to H(2)O(2) due to its bioelectrocatalytic reduction based on direct electron transfer between gold and HRP. The sensitivity of the gold electrodes modified with recombinant HRPs was in the range of 1.4-1.5 A M(-1) cm(-2) at -50 mV versus Agmid R:AgCl. The response to H(2)O(2) in the concentration range 0.1-40 microM was not dependent on the presence of a mediator (i.e. catechol) giving strong evidence that the electrode currents are diffusion limited. Lower detection limit for H(2)O(2) detection was 10 nM at the electrodes modified with recombinant HRPs.

Determination of BOD-values of starch-containing waste water by a BOD-biosensor

The control of waste water plants is difficult or even impossible using the classical determination method for biological oxygen demand (BOD), because of its high time consumption of five days. A determination within some minutes is possible by microbial BOD-sensors. However, high molecular weight substances cannot be detected, a problem which can be overcome by the use of additional enzymes. For the application in a flow-through system to analyse starch containing waste water, alpha-amylase and amyloglucosidase were immobilized by adsorption to polystyrene or polypropylene carriers followed by crosslinking. Furthermore, covalent coupling to different nylon carriers, derivatives of chitin, silanized glass beads and silanized beads of foamed glass was tried. Chitin and Lewatit were the best suited carriers for the immobilization of alpha-amylase and amyloglucosidase. Two glass columns were filled with the immobilized enzymes and inserted into a commercial BOD-sensor containing the yeast Trichosporon cutaneum as biological component. The system was stable for more than two months under storage and one month under working conditions. A comparison of different starch types resulted in a hydrolysis of more than 80% in case of potato starch whereas grain starch was hydrolized only for 40-50%. Sensor-determined BOD-values of waste water with potato starch were nearly identical with BOD5-values resulting from the classical method.