Electrode DNA-modified

DNA-Modified Electrodes. Molecular Recognition of DNA and Biosensor Applications... 

The initial hurdle to overcome in the biosensor application of a nucleic acid is that involving its stable attachment on a transducing element which commonly includes a metallic electrode. In the first part of this chapter, we wish to introduce our approach for DNA immobilization (Scheme 1). A detailed characterization of the immobilization chemistry is also presented. In the second part, we follow the development of work from our laboratory on chemical sensor applications of the DNA-modified electrode involving a biosensor for DNA-binding molecules and an electrochemical gene sensor. 

Cyclic voltammograms of the [Fe(CN)6] /Fe[(CN)g] redox couple with the bare and the DNA-modified electrodes are shown in Fig. 5 [14a]. The peak currents due to the reversible electrode reaction of the redox system on the bare Au electrode were significantly suppressed by the treatment with DNA. In contrast, the treatment with unmodified, native DNA made no suppression, and that with HEDS caused only a slight one, as seen in Fig. 

When natural or synthetic DNA molecules interact with electrode surfaces adsorption occurs. The knowledge about the adsorption of nucleic acids onto the electrode surface leads to the development of DNA-modified electrodes, also called electrochemical DNA biosensors [3-6,19-24], An electrochemical DNA biosensor is an integrated receptor-transducer device that uses DNA as the biomolecular recognition element to measure specific binding processes with DNA, using electrochemical transduction. 

The aim of developing DNA-modified electrodes is to study the interaction of DNA immobilized on the electrode surface with analytes in solution and to use the DNA biosensor to evaluate and to predict DNA interactions and damage by health hazardous compounds based on their ability to bind to nucleic acids. In this way, DNA acts as a promoter between the electrode and the biological molecule under study. 

Some similar features were observed concerning the adsorption and electrochemical oxidation of DNA on glassy carbon and tin oxide electrodes [68]. Differential pulse voltammograms were recorded in buffer solution without DNA after adsorption of DNA onto the electrode surface during a predetermined time at a fixed potential suggesting the possibility of using adsorption to preconcentrate DNA on solid electrode surfaces and use this DNA-modified electrode for analytical purposes. 

If we consider Figs. 3.8 and 3.9, where the results for the oxidation of guanosine and adenosine 5 -monophosphates at a bare glassy carbon electrode and at a DNA-modified electrode are presented, several facts are worth mentioning when comparing voltammograms at both electrodes. 

The DNA-modified electrodes have been used for trace measurements of toxic amine compounds [141], and for trace measurements of phenothia-zine compounds with neuroleptic and antidepressive action [142], as well as detection of radiation-induced DNA damage [143]. 

Electrochemical research on DNA is of great relevance to explain many biological mechanisms. The DNA-modified electrode is a very good model for simulating the nucleic acid interaction with cell membranes, potential environmental carcinogenic compounds and to clarify the mechanisms of action of drugs used as chemotherapeutic agents. 

All electrodes react with their environment via the surfaces in ways which will determine their electrochemical performance. Properly selected surface modification can effectively enhance the electrode heterogeneous catalysis property, especially selectivity and activity. The bulk materials can be chosen to provide mechanical, chemical, electrical, and structural integrity. In this part, several surface modification methods will be introduced in terms of metal film deposition, metal ion implantation, electrochemical activation, organic surface coating, nanoparticle deposition, glucose oxidase (GOx) enzyme-modified electrode, and DNA-modified electrode. 

Fig. 3.12 Schematic diagram of the process to fabricated DNA modified electrode (after Riccardi et al. 2006)...

Figure 5-9. Plot of the apparent formal potential of Ru(NI at a DNA-modified electrode. The concentration of Ru(NH3) " was adjusted such that I j , remained -10-20 pmol cm or approximately 5-10% of the value at saturation.

Figure 5-10. Cyclic voltammogram of MB recorded at a duplex DNA-modified electrode (sequence 5 -SH-AGT ACA GTC ATC GCG-3 ) at a sweep rate of 50 mV s in 50 mM sodium phosophate buffer, pH 6.5.

Figure 5-13. Plot showing the accumulated charge as a function of time following a potential step to -350 mV at a series of DNA-modified electrodes immersed in a solution containing 2 mM Fe(CN) and 0.5 pM MB. The thiol-terminated sequence (SI 1-5 -AOT ACA GTC ATC GCG-3 ) was hybridized before electrode deposition to its fully base-paired complement (TA), as well as complements that resulted in all of the possible single-base mismatches. Purine-purine, purine-pyrimidine, and pyiimidine-pyiimidine mismatches were all readily detected. (Adapted from ref. 13.)...

We used an anti-DNA antibody as an exploratory model system. The antibody was monoclonal from mouse sources and its subclass was IgM. Mouse IgG (MW 1.5 x 105 Da) and IgM (MW 9 x 105 Da) antibodies from normal plasma, and bovine serum albumin were used for the control measurements. To prevent the nonspecific adsorption of proteins to the uncovered, bare Au site in the modified electrode surface, the DNA-modified electrode prepared by the standard procedure was further treated with aqueous 2-mercaptoethanol solution and was used for the measurements. 

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