Combination of aptamer with gold nanoparticles for electrochemical signal amplification: application to sensitive detection of platelet-derived growth factor

In this paper, we report a novel electrochemical detection approach for platelet-derived growth factor (PDGF) via "sandwich" structure and gold nanoparticles (Au-NPs) mediated amplification technique. The "sandwich" structure is fabricated based on the fact that PDGF has two aptamer-binding sites, which makes it possible for one PDGF molecule to connect with two aptamers simultaneously. It is found that this electrochemical system with "sandwich" structure and Au-NPs can significantly amplify the signal of electrochemical probe [Ru(NH(3))(5)Cl](2+) for PDGF detection, and thus increase the detection sensitivity significantly. As a result, this PDGF detection approach obtains an extraordinarily low detection limit of 1 x 10(-14)M for purified samples, 1 x 10(-12)M for contaminated-ridden samples or undiluted blood serum. This detection approach can also exhibit good stability and excellent specificity.     

A simple electrochemical approach to fabricate a glucose biosensor based on graphene-glucose oxidase biocomposite

We report a simple electrochemical approach for the immobilization of glucose oxidase (GOx) on reduced graphene oxide (RGO). The immobilization of GOx was achieved in a single step without any cross linking agents or modifiers. A simple solution phase approach was used to prepare exfoliated graphene oxide (GO), followed by electrochemical reduction to get RGO-GOx biocomposite. The direct electrochemistry of GOx was revealed at the RGO-GOx modified glassy carbon electrode (GCE). The electrocatalytic and electroanalytical applications of the proposed film were studied by cyclic voltammetry (CV) and amperometry. It is notable that the glucose determination has been achieved in mediator-free conditions. RGO-GOx film showed very good stability, reproducibility and high selectivity. The developed biosensor exhibits excellent catalytic activity towards glucose over a wide linear range of 0.1-27mM with a sensitivity of 1.85μAmM(-1)cm(-2). The facile and easy electrochemical approach used for the preparation of RGO-GOx may open up new horizons in the production of cost-effective biosensors and biofuel cells.     

Electrochemical engineering approach to the irrigation of tooth canals under the influence of a vibrating file

Doubt exists concerning the irrigation of secondary tooth canals when the vibration of a file introduced into the main root canal is superimposed on flow-through irrigation of the main canal. Depending on the type of commercial equipment used, the vibrations of the file are sonic or ultrasonic. We use the methodology of an electrochemical engineering approach in a study of the intensity of the irrigation of the secondary canals under the influence of sonic and ultrasonic vibrations of a file located at various heights in the main canal. The tooth canals are simulated by small electrochemical cells containing electrodes located at the end of cavities simulating the secondary canals. An electrochemical method is used to measure the mass transfer coefficients at these electrodes, a classical method in electrochemical engineering laboratories. The values of the mass transfer coefficients are representative of the importance of the irrigation of the electrodes. Thus they give a quantitative idea of the vibrations on the irrigation of secondary tooth canals. The work demonstrates the usefulness of the electrochemical engineering approach in contributing to the solution of a biomedical problem.     

Electrochemical magneto immunosensing of antibiotic residues in milk

A novel electrochemical immunosensing strategy for the detection of sulfonamide antibiotics in milk based on magnetic beads is presented. Among the different strategies for immobilizing the class-specific anti-sulfonamide antibody to the magnetic beads--such as those based on the use of Protein A or carboxylate modified magnetic beads - ,the best strategy was found to be the covalent bonding on tosyl-activated magnetic beads. The immunological reaction for the detection of sulfonamide antibiotics performed on the magnetic bead is based on a direct competitive assay using a tracer with HRP peroxidase for the enzymatic labelling. After the immunochemical reactions, the modified magnetic beads can be easily captured by a magneto sensor made of graphite-epoxy composite (m-GEC), which is also used as the transducer for the electrochemical immunosensing. The electrochemical detection is thus achieved through a suitable substrate for the enzyme HRP and an electrochemical mediator. The electrochemical approach is also compared with a novel magneto-ELISA with optical detection. The performance of the electrochemical immunosensing strategy based on magnetic beads was successfully evaluated using spiked milk samples, and the detection limit was found to be 1.44 microg L(-1) (5.92 nmol L(-1)) for raw full cream milk. This strategy offers great promise for rapid, simple, cost-effective and on-site analysis of biological, food and environmental samples.     

Surface Enhanced Infrared Characterization Using Disordered Slit-Antenna Arrays for the Detection of Electrodeposited Cytochrome C

Plasmonics - An approach which allows both electrochemical studies and surface enhanced infrared characterization of electrodeposited Cytochrome C is presented. This approach is based on in-plane...     

Stimulation of acid phosphatase induction in Saccharomyces cerevisiae by electrochemical modulation of effector concentration

A novel modulating method of the expression of Saccharomyces PHO 5 gene, responsible for acid phosphatase (APase), is proposed. The method is based on electrochemical modulation of an effector (inorganic phosphate) concentration, as the gene expression is initiated below a threshold concentration of phosphate and is terminated above the threshold value. By positioning the yeast in the close neighborhood of a conducting polymer, the authors show the effectiveness of the electrochemical approach toward PHO 5 induction. Based on the approach, phosphate concentration is easily modulated at the boundary concentration by taking advantage of anion doping-undoping at a conducting polymer and the resulting anion localization-delocalization in the polymer, as the local enrichment of phosphate in the polymer results in the lowering of phosphate in the vicinity of polypyrrole. External phosphate concentration is thus electrochemically modulated when the conducting polymer is positioned in the close neighborhood of the yeast cells; thereby the PHO gene is induced. Here an electrochemical approach for the APase expression as a strategy of selective induction of specific genetic information is described. (c) 1993 John Wiley & Sons, Inc.     

A facile strategy for nonenzymatic glucose detection

Glassy carbon electrode modified with boron oxide nanoparticles supported on multiwall carbon nanotubes was obtained via a facile approach. The as-prepared modified electrode exhibits excellent electrocatalytic activity toward the redox of glucose in pH 7.0 phosphate buffer solution. The electrochemical response of the modified electrode to glucose shows a linear range of 1.5-260 μM with a correlation coefficient of 0.9986 and the calculated detection limit is 0.8 μM at a signal-to-noise ratio of 3, which makes it useful for developing the electrochemical determination of glucose concentrations without using glucose oxidase at physiological pH.     

Internal standard method for the measurement of choline and acetylcholine by capillary electrophoresis with electrochemical detection

An internal standard method has been developed for the determination of the neurotransmitter acetylcholine and/or its metabolic precursor choline. This approach couples the high separation efficiency of capillary electrophoresis with the sensitivity and selectivity of electrochemical detection at an enzyme-modified electrode. Indirect electrochemical detection is accomplished at a 25 microm platinum electrode modified by cross-linking the enzymes choline oxidase and acetylcholinesterase with glutaraldehyde. Although in this simple form of electrode fabrication there is a gradual loss of response from the electrochemical detector with time, accurate quantitation is achieved by the addition of butyrylcholine, which is also a substrate for acetylcholinesterase, as an internal standard. A linear response is achieved between 0 and 125 microM with a limit of detection of 2 microM (25 fmol). The utility of this method was demonstrated by monitoring the kinetics of choline uptake in synaptosomal preparations.     

Construction of bacterial artificial chromosome library from electrochemical microorganisms

A microbial fuel cell is a device that directly converts metabolic energy into electricity, using electrochemical technology. The analysis of large genome fragments recovered directly from microbial communities represents one promising approach to characterizing uncultivated electrochemical microorganisms. To further assess the utility of this approach, we constructed large-insert (140 kb) bacterial artificial chromosome (BAC) libraries from the genomic DNA of a microbial fuel cell, which had been operated for three weeks using acetate media. We screened the expression of several ferric reductase activities in the Escherichia coli host, in order to determine the extent of heterologous expression of metal-ion-reducing enzymes in the library. Phylogenetic analysis of 16S rRNA gene sequences recovered from the BAC libraries indicates that they contain DNA from a wide diversity of microbial organisms. The constructed bacterial library proved a powerful tool for exploring metal-ion reductase activities, providing information on the electron transport pathway of electrochemical microbial (ECM) organisms.     

Electrochemical studies of danthron and the DNA-danthron interaction

Danthron is an important natural occurring component in laxative drugs. In this paper, electrochemical investigation of danthron and its interaction with DNA is reported. Via the electrochemical approach assisted by ultraviolet-visible (UV-Vis) spectroscopy, we have proved that danthron intercalates into DNA strands forming some nonelectroactive complexes, which results in the decrease of redox peak currents of danthron. In addition, the decrease of the peak currents is proportional to the concentration of DNA. The difference between the interaction of danthron with double-stranded DNA (dsDNA) and with single-stranded DNA (ssDNA) has also been studied. This character implies the potential of danthron to discriminate dsDNA and ssDNA.     

A graphene screen-printed carbon electrode for real-time measurements of unoccupied active sites in a cellulase

Cellulases hydrolyze cellulose to soluble sugars and this process is utilized in sustainable industries based on lignocellulosic feedstock. Better analytical tools will be necessary to understand basic cellulase mechanisms, and hence deliver rational improvements of the industrial process. In this work we describe a new electrochemical approach to the quantification of the populations of enzyme that are respectively free in the aqueous bulk, adsorbed to the insoluble substrate with an unoccupied active site or threaded with the cellulose strand in the active tunnel. Distinction of these three states appears essential to the identification of the rate-limiting step. The method is based on disposable graphene-modified screen-printed carbon electrodes, and we show how the temporal development in the concentrations of the three enzyme forms can be derived from a combination of the electrochemical data and adsorption measurements. The approach was tested for the cellobiohydrolase Cel7A from Hypocrea jecorina acting on microcrystalline cellulose, and it was found that the threaded enzyme form dominates for this system while adsorbed enzyme with an unoccupied active site constitutes less than 5% of the population.     

Selective glucose detection based on the concept of electrochemical depletion of electroactive species in diffusion layer

A glucose detection approach based on the concept of electrochemical depletion of electroactive species in diffusion layer was established, using scanning electrochemical microscopy (SECM). By controlling the glucose oxidase (GOD) modified electrode (substrate electrode) at a proper potential of electrochemical oxidation of interfering electroactive species, i.e., ascorbic acid (AA), an interference-free microcircumstance was formed in the diffusion layer of the substrate electrode. Consequently, we could successfully sense hydrogen peroxide generated from an enzymatic reaction by locating a Pt ultramicroelectrode (UME) (tip electrode, 5 microm in radius) into the diffusion layer of the substrate electrode. Properties of this interference-removing approach based on electrochemical depletion were systematically investigated. Results showed that the interference-removing efficiency was significantly determined by the tip-substrate distance and substrate potential. When the tip-substrate distance was 11 microm (2.2 times of the tip electrode radius) and the substrate potential was 0.5 V, nearly 90% of AA (0.5 mM) could be depleted within 30s without consumption of H2O2. Under these conditions, 0.1 mM AA showed no influence on the detection of 0.5 mM glucose. The linear range of glucose detection is 0.01-1 mM with a detection limit (DL) of 0.005 mM (correlation coefficient is 0.9948). This research will open a new way for developing selective micro-biosensors.     

Creation of 3D Textured Graphene/Si Schottky Junction Photocathode for Enhanced Photo‐Electrochemical Efficiency and Stability

This work presents a novel photo‐electrochemical architecture based on the 3D pyramid‐like graphene/p‐Si Schottky junctions. Overcoming the conventional transfer technique by which only planar graphene/Si Schottky junctions are currently available, this work demonstrates the 3D pyramid‐like graphene/p‐Si Schottky junction photocathode, which greatly enhances light harvesting efficiency and exhibits promising photo‐electrochemical performance for hydrogen generation. The formation of 3D pyramid‐like graphene/p‐Si Schottky junctions exhibits enhanced electrochemical activity and promotes charge separation efficiency compared with the bare pyramid Si surface without graphene. The inherent chemical inertness of graphene significantly improves the operational stability of 3D graphene/p‐Si Schottky junction photo‐electrochemical cells. The 3D pyramid‐like graphene/p‐Si Schottky junction photocathode delivers an onset potential of 0.41 V and a saturated photocurrent density of ?32.5 mA cm^?2 at 0 V (vs RHE) with excellent stability comparable to values reported for textured or nanostructured p‐Si photocathodes coated with ultrathin oxide layers by the conventional atomic layer deposition technique. These results suggest that the formation of graphene/Si Schottky junctions with a 3D architecture is a promising approach to improve the performance and durability of Si‐based photo‐electrochemical systems for water splitting or solar‐to‐fuel conversion.     

Sensitive immobilization-free electrochemical DNA sensor based on isothermal circular strand displacement polymerization reaction

A highly sensitive electrochemical DNA sensor that requires no probe immobilization has been developed based on a target recycling mechanism utilizing a DNA polymerase with a strand displacement activity. The electrochemical detection is realized by taking advantage of the difference in diffusivity between a free ferrocene-labeled peptide nucleic acid (Fc-PNA) and a Fc-PNA hybridized with a complementary DNA, while the DNA polymerase-assisted target recycling leads to signal generation and amplification. The hybridization of the target DNA opens up a stem-loop template DNA with the Fc-PNA hybridized to its extruded 5' end and allows a DNA primer to anneal and be extended by the DNA polymerase, which results in sequential displacement of the target DNA and the Fc-PNA from the template DNA. The displaced target DNA will hybridize with another template DNA, triggering another round of primer extension and strand displacement. The released Fc-PNA, due to its neutral backbone, has much higher diffusivity towards a negatively charged electrode, compared to that when it is hybridized with a negatively charged DNA. Therefore, a significantly enhanced signal of Fc can be observed. The outstanding sensitivity and simplicity make this approach a promising candidate for next-generation electrochemical DNA sensing technologies.     

Enhanced redox conductivity and enriched Geobacteraceae of exoelectrogenic biofilms in response to static magnetic field

Applied Microbiology and Biotechnology - A possible approach to enhance the performance of microbial electrochemical system such as microbial fuel cells is to increase the conductivity of catalytic...     

Electrochemical reduction of cytochromes P450 using electrodes containing immobilized substrates

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

Power production enhancement with a polyaniline modified anode in microbial fuel cells

In this paper, an approach of improving power generation of microbial fuel cells (MFCs) by using a HSO(4)(-) doped polyaniline modified carbon cloth anode was reported. The modification of carbon cloth anode was accomplished by electrochemical polymerization of aniline in 5% H(2)SO(4) solution. A dual-chamber MFC reactor with the modified anode achieved a maximum power density of 5.16 Wm(-3), an internal resistance of 90 Ω, and a start-up time of 4 days, which was respectively 2.66 times higher, 65.5% lower, and 33.3% shorter than the corresponding values of the MFC with unmodified anode. Evidence from X-ray photoelectron spectroscopy and scanning electron microscopy results proved that the formation of biofilm on the anode surface could prevent the HSO(4)(-) doped polyaniline to be de-doped, and the results from electrochemical tests confirmed that the electrochemical activity of the modified anode was enhanced significantly after inoculation. Charge transfer was facilitated by polyaniline modification. All the results indicated that the polyaniline modification on the anode was an efficient approach of improving the performance of MFCs.     

A new format of electrodes for the electrochemical reduction of cytochromes P450

New approach to the electrochemical reduction of cytochromes P450 (P450s, CYPs) at electrodes chemically modified with appropriate substrates for P450s ("reverse" electrodes) was proposed. The method is based on the analysis of cyclic voltammograms, square-wave voltammograms and amperograms with subsequent determination of electrochemical characteristics such as catalytic current and redox potential. The sensitivity of proposed method is 0.2-1 nmol P450/electrode. The changes of maximal current and of redox potentials in square-wave voltammograms as well as the changes of catalytic current in amperometric experiments proved to be informative and reliable. Planar regime of screen-printed electrodes (strip-type sensors) enabled to utilise 20-60 microl of electrolyte volume. The enzyme-substrate pairs P450 2B4/benzphetamine and P450scc/cholesterol were investigated. Electrochemical parameters of electrodes with unspecific P450 substrates differed considerably from electrodes with appropriate substrates.     

Electronic detection of DNA mutation based on strand exchange reaction

A new approach to electronic detection of a single base mismatch is described. The assay involves the electrochemical measurements of DNA strand exchange reactions (SERs) between electrode-bound redox-modified DNA duplex and target DNA, where the sequence of redox-modified DNA is exchangeable to that of the target DNA. The presence of a single base mismatch can be determined from the slower SER rates compared with fully matched DNA.     

Triplex signal amplification for electrochemical DNA biosensing by coupling probe-gold nanoparticles-graphene modified electrode with enzyme functionalized carbon sphere as tracer

An ultrasensitive electrochemical DNA biosensor was constructed by assembling probe labeled gold nanoparticles (ssDNA-AuNP) on electrochemically reduced graphene oxide (ERGO) modified electrode with thiol group tagged (GT) DNA strand (d(GT)(29)SH) and coupling with horseradish peroxidase (HRP) functionalized carbon sphere (CNS) as tracer. The heteronanostructure formed on the biosensor surface appeared relatively good conductor for accelerating the electron transfer, while the HRP tagged CNS provided dual signal amplification for electrochemical biosensing. The triplex signal amplification strategy produced an ultrasensitive electrochemical detection of DNA down to attomolar level (5 aM) with a linear range of 5 orders of magnitude (from 1 × 10(-17)M to 1 × 10(-13)M), and appeared high selectivity to differentiate single-base mismatched and three-base mismatched sequences of DNA. The proposed approach provided a simple and reliable method for DNA detection with high sensitivity and specificity, indicating promising application in bioanalysis and biomedicine.