Simultaneous differentiation and quantification of ricin and agglutinin by an antibody-sandwich surface plasmon resonance sensor.

Ricin is one of the most toxic plant toxins known. Its accessibility and relative ease of preparation makes it a potential agent for criminal or bio-terrorist attacks. Detection of ricin from unknown samples requires differentiation of ricin from the highly homologous Ricinus communis agglutinin which is currently not feasible using immunological methods.

Cytochrome c and superoxide: a reply.

In his comments, W.H. Koppenol criticizes our article with respect to our conclusions and procedures.

Differently substituted sulfonated polyanilines: the role of polymer compositions in electron transfer with pyrroloquinoline quinone-dependent glucose dehydrogenase.

Sulfonated polyanilines have become promising building blocks in the construction of biosensors, and therefore we use here differently substituted polymer forms to investigate the role of their structural composition and properties in achieving a direct electron transfer with the redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH). To this end, new copolymers containing different ratios of 2-methoxyaniline-5-sulfonic acid (MAS), 3-aminobenzenesulfonic acid (ABS) and 3-aminobenzoic acid (AB) units have been chemically synthesized. All polymers have been studied with respect to their ability to react directly with PQQ-GDH.

Mechanistic insights into the superoxide-cytochrome c reaction by lysine surface scanning.

This study summarizes results which have been obtained by a mutational study of human cytochrome c. The protein can be used as a recognition element in analytical assays and biosensors for superoxide radicals since ferricytochrome c reacts with superoxide to form ferrocytochrome c and oxygen. Here lysine mutagenesis of the distal surface (i.

Quantum dots on electrodes--new tools for bioelectroanalysis.

The review covers recent developments in which quantum dots (QDs) are combined with electrodes for detection of analytes. Special focus will be on the generation of photocurrents and the possibility of spatially resolved, light-directed analysis. Different modes for combining biochemical reactions with QDs will be discussed.

Insights into the formation and operation of polyaniline sulfonate/cytochrome c multilayer electrodes: contributions of polyelectrolytes' properties.

The multilayer formation of two different sulfonated polyanilines with cytochrome c is presented and mechanistic aspects of the contributions of the polyelectrolytes' properties to the characteristics of the assemblies are discussed. These two modified polymers, PASA1 and PASA2 are chemically synthesized and differ in the grade of sulfonation, substitution, and the chain length of the polymer. The influence of these properties on the multilayer assembly with cytochrome c is studied in detail by Quartz Crystal Microbalance (QCM) technique and Cyclic Voltammetry (CV).

Layer-by-layer assembly of electro-active gold nanoparticle/cytochrome c multilayers.

In this study we have tested the use of modified gold nanoparticles (GNPs) for introduction into cytochrome c (CytC) multilayer assemblies, constructed by the layer-by-layer deposition technique. For this purpose gold nanoparticles of different size are synthesized and the GNPs modified with mercaptopropionic acid (MPA). The particles are characterized by UV-vis-spectroscopy and transmission electron microscopy (TEM).

Self-assembly of electro-active protein architectures on electrodes for the construction of biomimetic signal chains.

The layer-by-layer adsorption technique based on the consecutive deposition of oppositely charged species is suitable for the preparation of protein multilayers with fully electro-active protein molecules. The methodology was established with cytochrome c and the polyelectrolyte sulfonated polyaniline (PASA). The technique is also useful for the construction of bi-protein architectures confining protein-protein communication to an electrode.

Photoelectrochemical signal chain based on quantum dots on gold--sensitive to superoxide radicals in solution.

A photoelectrochemical signal chain sensitive to the presence of superoxide radicals was developed on the basis of CdSe/ZnS quantum dots which were immobilized on gold electrodes using a dithiol compound. The conditions of photo current generation under illumination have been characterized with respect to the dependence on the applied electrode potential, the wavelength of the light beam and the stability of the measurement. Because of photoexcitation electron-hole pair generation is enforced in the nanoparticles enhancing the conductivity of the quantum dot layer.

The use of electrochemical impedance spectroscopy for biosensing.

This review introduces the basic concepts and terms associated with impedance and techniques of measuring impedance. The focus of this review is on the application of this transduction method for sensing purposes. Examples of its use in combination with enzymes, antibodies, DNA and with cells will be described.

Electrocatalytically functional multilayer assembly of sulfite oxidase and cytochrome c.

An electrocatalytically functional multilayer has been designed using two proteins, cytochrome c and sulfite oxidase, and a polyelectrolyte (polyaniline sulfonate). The two proteins were co-immobilized on the surface of a gold electrode in alternating layers by electrostatic interactions using the layer-by-layer technique. The formation of this fully electro-active multilayer is characterized by quartz crystal microbalance and electrochemical experiments.

Impedance spectroscopy and biosensing.

This chapter introduces the basic terms of impedance and the technique of impedance measurements. Furthermore, an overview of the application of this transduction method for analytical purposes will be given. Examples for combination with enzymes, antibodies, DNA but also for the analysis of living cells will be described.