Redox-active probe

The interfacial capacitance can also provide a significant insight into the permeability of interfacial supramolecular assemblies. While information of this kind complements studies using redox-active probes in solution, it also provides information on a significantly shorter length scale, i.e. that of electrolyte ions and solvent molecules. For example, for dense, defect-free monolayers, the limiting capacitance is very much lower (5-10 pF cm-2) than that found for an unmodified interface (20-60 pF cm 2). 

Electroactive dendrimers are defined as those that contain functional groups capable of undergoing fast electron transfer reactions [85], The combination of specific electron transfer properties of redox active probes with the unique structural properties of dendrimers offers attractive prospects of their exploitation in electrocatalytic processes of biological and industrial importance [86], Further, the interest in dendrimers containing electroactive units also relies on the fact that electrochemistry is a powerful technique to elucidate the structure and purity of dendrimers, to evaluate the degree of electronic interaction of their chemically and/or topologically equivalent or non- equivalent moieties, and also to study their endo- and exo-receptor capabilities [87],... 

An alternative approach for utilizing DNA thin films for electrochemical sensors involves using redox-active probe molecules intercalated into the Ji-stack. Fig 5-lb. This approach has been successfully employed in the design of electrochemical assays for hybridization,single-base mismatches, and chemical modifications and lesions within duplex DNA. It has also provided provocative experimental results regarding charge transport through the double helix. ... 

The aptamer described above was attached to the surface of the silica colloidal crystal comprising 290 nm silica spheres (resulting in 22.5 nm radius nanopores) via maleimide-activated support. The transport rate of a redox-active probe molecule (ferrocene dimethanol) through the resulting nanoporous films was measured as a function of cocaine concentration using cyclic voltammetry. A neutral redox probe, Fc(CH20H)2, was used to exclude the possibility that the observed changes in the molecular transport would result from electrostatic effects [26,27]. 

Different stimuli could trigger the transition of the smart polymer making it possible to produce membranes whose permeabihties respond to these stimuh. When a copolymer of NIPAAM with triphenylmethane leucocianide was grafted to the membrane, it acquired photosensitivity—uv irradiation increases permeation through the membrane (78). Fully reversible, pH-switchable permselectivity for both cationic and anionic redox-active probe molecules was achieved by depositing composite films formed from multilayers of amine-terminated dendrimers and poly(maleic anhydride-co-methylvinyl ether) on gold-coated silicon (79). 

Thus, the magnitude of i s can provide an insight into the electrode size and shape when a redox-active probe of known concentration and diffusion coefficient is used. Alternatively, once the electrode geometry is known, the limiting current can be used to determine the concentration of redox species. Moreover, the shape of the voltammogram can be analyzed to provide useful information about the rate of heterogeneous electron transfer across the electrode/ solution interface. 

Aptamer based biosensors, for example for recombinant human erythropoietin (as model analyte), can be made more sensitive by amplification with a boronic acid tethered gold nanoparticle that is then associated with an alkaline phosphatase to produce a redox active probe molecule. A similar re-usable bio-immuno-sensor has been suggested for carcinoembryonic antigen. A phenylboronic acid is assembled on gold to (reversibly) bind the antibody horseradish peroxidase conjugate. Interaction with the antigen slows down the hydrogen peroxide reduction. An HIV-1 immunoassay based on electroluminescence has been proposed by Zhou etaV In this process the... 

Figure 8.13 Schematic description of a triple amplification method for microRNA sensing based on (i) DNA-microRNA recognitions, (ii) boronic acid attachment of gold nanoparticles with biotin, (iii) binding streptavi-din with phosphatase, and finally (iv) release of the redox active probe. (Reproduced from ref. 95 with the permission of Elsevier.)...

Figure 1.4 (a) General DNA biosensor design (b) Electrochemical detection of DNA hybridization based on intercalative redox active probe (c) Electrochemical detection using redox active probe. 

Label-based electrochemical detection of DNA hybridization a. Intercalative redox active probe... 

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