Guanine electrocatalytic

It has been shown that complexes that participate only in outer-sphere electron transfer oxidize guanine electrocatalytically if the potential of the metal complex is greater than 0.9 V (199). Shown in Fig. 18 are cyclic voltammograms of Rufbpyls " with and without calf thymus DNA (200). The catalytic enhancement is observed for calf thymus DNA, poly(GC), or oligomers containing G, but not for poly(AT). 

A. Abbaspour and M.A. Mehrgardi, Electrocatalytic oxidation of guanine and DNA on a carbon paste electrode modified by cobalt hexacyanoferrate films. Anal. Chem. 76, 5690-5696 (2004). 

An electrocatalytic oxidation of guanine in oligonucleotides and DNA using the [Ru(bpy)3] +/ + redox couple has been observed and its mechanism investigated [261]. Metal-polypyridine complexes with 0x0 ligands act as electrochemical catalysts of water, Cl, or hydrocarbon oxidations [128, 166, 167, 262]. 

The surface coverage (T) and heterogeneous electron transfer rate constant (ks) of adsorbed redox couple were about 9.5 10 9 mol cm 2 and 3.18 ( 0.20) s 1, respectively, indicating the high loading ability of ZnOx nanoparticles toward guanine oxidation product and great facilitation of the electron transfer between redox couple and ZnOx nanoparticles. The modified electrode exhibited excellent electrocatalytic activity toward L-cysteine oxidation. The kcat for L-cysteine oxidation was found to be 4.20( 0.20)x 103 M V1. The catalytic oxidation current allows the amperometric detection of L-cysteine at potential of 0.5 V with detection limit of 50 nM, linear response up to 20 p, M and sensitivity of 215.4 nA.p A" em"2 This results indicate ZnO nanoparticles modified electrodes are suitable microenvironment for observation and stabilization of unusual and unstable redox couples. 

The ability to calculate redox potentials has powerful implications. For example, electrocatalytic reactions of metal complexes, such as Ru(bpy)3 +, with DNA nucleobases, such as guanine, provide a sensitive method for detection of nucleic acids on surfaces in electrochemical DNA chips see Nucleic Acid-Metal Ion Interaction In these reactions. 

One limitation of electrocatalytic detection for nucleic acid detection was its limitation to native guanine as an... 

There are a variety of methods to detect the DNA content of food, which can be used to unequivocally identify the nature of the product [4]. Among the various systems for nucleic acid detection, electrochemical DNA analysis can involve direct detection based on a guanine signal (label-free) [5] or an electrocatalytic mechanism (label-based). Quantum dots (QDs) [6,7], metal nanoparticles (NPs) [8,9], enzymes [10,11], and metal complexes [12, 13] can be employed as labels. This chapter focuses on electrochemical biosensing systems based on DNA hybridization events, which offer novel routes for food safety and security applications. Particularly, it describes in detail different approaches reported in the latest years on the immobilization of oligonucleotides on electrochemical transducers for sensing of various compounds with interest in food industry. In addition, some interesting applications in other fields that can easily be extended to that of food are also included. 

Figure 10.2 Scheme of label-free hybridization commonly used in electrochemical DNA hybridization sensors, (a) Target DNA guanine bases on carbon electrode after the hybridization. (b) Representation of the electrocatalytic oxidation of guanine on ITO electrode by means of redox mediator, (c) Increase the electron transfer resistance by use an electroactive redox couple and a gold electrode surface. Reproduced from [25], with permission from American Chemical Society... 

The electrocatalytic oxidation of guanine on a ruthenated porphyrin film deposited on indium-tin oxide electrode was spectroelectrochemicaUy monitored... 

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