Arben Merkoçi

Low-Potential Stable NADH Detection at Carbon-Nanotube-Modified Glassy Carbon Electrodes

Abstract Carbon-nanotube (CNT)-modified glassy carbon electrodes exhibiting strong and stable electrocatalytic response toward NADH are described. A substantial (490 mV) decrease in the overvoltage of the NADH oxidation reaction (compared to ordinary carbon electrodes) is observed using single-wall and multi-wall carbon-nanotube coatings, with oxidation starting at ca. −0.05 V (vs. Ag/AgCl; pH 7.4). Furthermore, the NADH amperometric response of the coated electrodes is extremely stable, with 96% and 90% of the initial activity remaining after 60 min stirring of 2×10−4 and 5×10 −3 M NADH solutions, respectively (compared to 20% and 14% at the bare surface). The CNT-coated electrodes thus allow highly sensitive, low-potential, stable amperometric sensing. Such ability of carbon nanotubes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.

Configurations used in the design of screen-printed enzymatic biosensors. A review

Abstract Different thick-film biosensor configurations designed during the last decade are revised. These planar configurations are classified in three groups: (a) multiple-layer deposition (biological deposition by hand or electrochemically), (b) screen-printing of composite inks or pastes using two or more steps (biological deposition by screen-printing), (c) one-step deposition layer or biocomposite strategy. Different enzyme immobilisation procedures corresponding to these configurations are also revised. These procedures consist mainly of enzyme adsorption onto transducer surface, biological immobilisation by cross-linking in a glutaraldehyde layer, and physical, electro- or UV-polymerisation entrapment. Immobilisation into the bulk of different carbon-based inks or pastes is also presented.

Electrochemical genosensor design: immobilisation of oligonucleotides onto transducer surfaces and detection methods

The present report reviews immobilisation techniques of purified oligonucleotides on electrochemical transducers and their corresponding detection techniques. Most of the literature reviewed was published in the 1990s. The immobilisation techniques of a DNA probe to the surface of an electrochemical transducer made from carbon, gold, platinum or polypyrrole, ranged from simple adsorption to covalent bonding. Recent efforts to couple the recognition layer containing the immobilised nucleic acid recognition layer with the electrochemical signal transducer are discussed. Special attention is given to hybridisation biosensing based on electroactive indicators.

Carbon nanotubes and graphene in analytical sciences

AbstractNanosized carbon materials are offering great opportunities in various areas of nanotechnology. Carbon nanotubes and graphene, due to their unique mechanical, electronic, chemical, optical and electrochemical properties, represent the most interesting building blocks in various applications where analytical chemistry is of special importance. The possibility of conjugating carbon nanomaterials with biomolecules has received particular attention with respect to the design of chemical sensors and biosensors. This review describes the trends in this field as reported in the last 6xa0years in (bio)analytical chemistry in general, and in biosensing in particular.n FigureCarbon nanotubes and graphene in analytical applications

Electrochemical stripping detection of DNA hybridization based on cadmium sulfide nanoparticle tags

Abstract We report on the detection of DNA hybridization in connection to cadmium sulfide nanoparticle tracers and electrochemical stripping measurements of the cadmium. A nanoparticle-promoted cadmium precipitation is used to enlarge the nanoparticle tag and amplify the stripping DNA hybridization signal. In addition to measurements of the dissolved cadmium ion we demonstrate solid-state measurements following a ‘magnetic’ collection of the magnetic-bead/DNA-hybrid/CdS-tracer assembly onto a thick-film electrode transducer. The new protocol combines the amplification features of nanoparticle/polynucleotides assemblies and highly sensitive stripping potentiometric detection of cadmium, with an effective magnetic isolation of the duplex. The low detection limit (100 fmol) is coupled to good reproducibility (RSD=6%). Prospects for using binary inorganic colloids for multi-target detection are discussed.

New materials for electrochemical sensing. IV. Molecular imprinted polymers

Molecular imprinted polymers (MIPs) have become an important tool in the preparation of artificial and robust recognition materials capable of mimicking natural systems. When compared with natural molecular recognition products, such as antibodies, MIPs bring several advantages, such as low-cost, predictable specificity, durability and mass production. An overview of the use of MIPs for the design of electrochemical sensors based on different signal-transduction schemes is presented here. The revised transduction schemes include capacitive, conductometric, voltammetric and potentiometric sensors. The coupling of MIPs with these transducers is still at an early stage.

Electrochemical biosensing with nanoparticles

This minireview looks at the latest trends in the use of nanoparticles (NPs) in electrochemical biosensing systems. It includes electrochemical characterization of NPs for use as labels in affinity biosensors and other applications. DNA analysis involving NPs is one of the most important topics of current research in bionanotechnology. The advantages of the use of NPs in designing novel electrochemical sensors for DNA analysis are reviewed. Electrochemical NPs can also be used in designing immunoassays, offering the possibility of easy, low cost and simultaneous detection of several proteins. Research into NP applications in electrochemical analysis is in its infancy. Several aspects related to sensitivity as well integration of all the assay steps into a single one need to be improved.

Pesticide determination in tap water and juice samples using disposable amperometric biosensors made using thick-film technology

Abstract A new design of biosensor strips for pesticide analysis is presented. The developed biosensors integrate a photolithographic conducting copper track, graphite–epoxy composite applied by screen-printing and enzyme (AChE or BChE) immobilised manually by crosslinking with glutaraldehyde. Detection limits in the order of 10 −10 to 10 −11 xa0M pesticides (paraoxon and carbofuran) have been achieved in standard solutions. Pesticide analysis have been realised on spiked real samples of tap water and fruit juice, with recovering percentages close to 100%, corroborating that the biosensor is sensitive enough to detect pesticides in these matrices.

Particle-based detection of DNA hybridization using electrochemical stripping measurements of an iron tracer

Abstract Two particle-based procedures for monitoring DNA hybridization based on electrochemical stripping detection of an iron tracer are described. The first protocol involves probes labeled with gold-coated iron core–shell nanoparticles, while the second route relies on detecting the iron content of magnetic-sphere tags. In both cases, the captured iron-containing particles are dissolved following the hybridization, and the released iron is quantified by cathodic-stripping voltammetry in the presence of the 1-nitroso-2-naphthol ligand and a bromate catalyst. Both protocols offer high sensitivity, a well-defined concentration dependence, and minimal contributions from non-complementary nucleic acids. The iron-containing particle signal amplifiers thus represent a very useful addition to the arsenal of metal tracers employed in electrical bioassays.

Determination of Toxic Substances Based on Enzyme Inhibition. Part II. Electrochemical Biosensors for the Determination of Pesticides Using Flow Systems

Enzyme inhibition coupled to flow injection systems set-ups are a powerful tool for the monitoring of environmental toxics. The present review examines the latest contributions to this field where electrochemical detection is used. The advantages and limitations of the FIA technique in the context of enzyme inhibition analytical procedures are discussed. The present review is organized in accordance to the enzyme (cholinesterases, tyrosinases, or alkaline phosphatase) used in the measurement.