DNA-immobilized electrode

Such concentration-dependent changes in CV profiles on the DNA-immobilized electrode were not seen for Na ion in the concentration range of 10" -10" M. The effect of quinacrine upon the peak recovery was thus much stronger than that of NaCl 8 X 10 M of the drug seems sufficient to cancel the electrostatic repulsion, whereas 10 M of NaCl does not at all. This can be attributed to the specific and strong interaction between DNA double helix and quinacrine (25). 

Takenaka S, Uto Y, Takagi M, Kondo H (2005) Enhanced electron transfer from glucose oxidase to DNA-immobilized electrode aided by ferrocenyl naphthalene diimide, a threading interealator. Chem Lett 27 989-990... 

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. 

FIG. 7 The quinacrine-dependent changes in cyclic voltammograms of the DNA-immobilized An electrode. Experimental conditions are the same as those in Fig. 5. 

DNA immobilized by organosilane chemistries has proven to be an effective method for measuring impedance changes upon hybridization using both gold and platinum electrodes [21,50]. The effect of different silane chemistries creates differences in the hydrophobicity and hydration levels of the modified surface. The organosilane treatment along with the ssDNA... 

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. 

A.M. Oliveira Brett and A.-M. Chiorcea, Atomic force microscopy of DNA immobilized onto a highly oriented pyrolytic graphite electrode surface, Langmuir, 19 (2003) 3830-3839. 

Scheme 27.1. Electrochemical sensing of DNA by using disposable graphite electrodes (1) DNA immobilization onto pretreated PGE(s) using dip-coating procedure after dipped into each vial separately (A) or into the same vial (B). (2) Washing step by using ABS for 5 s. (3) DPV measurement in ABS. (4) Electrochemical detection of DNA.

The overall performance of this electrochemical DNA sensing method based on disposable electrodes was explored for optimum experimental conditions in order to detect DNA in higher sensitivity and selectivity. For this purpose, the effect of DNA immobilization time onto PGEs was studied followed by dip-coating procedure. 

Fig. 4 Influence of the potential applied to the working electrode during the immobilization step on the guanine peak area. Electrode pretreatment + 1.6 V vs Ag/AgCl. ss-DNA immobilization 5 mg L-1 for 2 min chronopotentiometry conditions 2 x SSC buffer pH 7.4 with a stripping constant current of + 2 jxA and an initial potential of + 0.5 V...

In Fig. 4 the influence of the potential applied to the working electrode on the guanine peak area during DNA immobilization is shown. The guanine peak area increases till a value of + 0.8 V vs. Ag pseudo-reference SPE, (even if the higher value obtained is for + 0.5 V), then the peak area decreases when the value of the applied potential is close to the value of guanine oxidation. 

Chitosan has been utilized along with hydrothermally prepared nano-ZnO nanoparticles for DNA hybridization detection. The detection limit is obtained as 1.09 x 10"11 mol L 1 of complementary target [66], A MWNTs/nanoZnO/CH modified nanocomposite GCE electrode has been used for DNA immobilization via physisorption. This biosensor can effectively discriminate different DNA sequences related to PAT gene in the transgenic com, with detection limit of 2.8 x K)"12 mol/L of target sequence [67], In another report they have deposited ZnO nanoparticles, MWNTs and CH layer onto glassy carbon electrode to immobilize ssDNA probe. A remarkable synergistic effect of the ZnO nanoparticles and MWNTs has been achieved after ssDNA probe immobilization for fabrication of sensitive electrochemical DNA biosensor. The modified electrode shows a wide linear response for DNA hybridization detection. (1.0 x 10"11 to 1.0 x 10"6 mol/L) with detection limit of 2.8 x 1 O 12 mol/L [68],... 

Electrostatic DNA immobilization on electrode surface may require longer accumulation time periods than 5 min. Adjustment of accumulation time periods according to the concentration of DNA sample and electrode surface is recommended. For example, the immobilization of a trace amount of DNA onto a carbon paste electrode with a large surface area would certainly require a long accumulation time, while stirring the DNA containing solution. 

The electrochemical procedure to build up the DNA biosensor included four main steps electrochemical conditioning of the electrode surface in order to oxidize the graphite impurities and to obtain a more hydrophilic surface to avoid DNA immobilization, calf thymus dsDNA immobilization, interaction with the sample solution, and electrode surface interrogation. 

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