DNA adsorption

Nucleic acids, DNA and RNA, are attractive biopolymers that can be used for biomedical applications [175,176], nanostructure fabrication [177,178], computing [179,180], and materials for electron-conduction [181,182]. Immobilization of DNA and RNA in well-defined nanostructures would be one of the most unique subjects in current nanotechnology. Unfortunately, a silica surface cannot usually adsorb duplex DNA in aqueous solution due to the electrostatic repulsion between the silica surface and polyanionic DNA. However, Fujiwara et al. recently found that duplex DNA in protonated phosphoric acid form can adsorb on mesoporous silicates, even in low-salt aqueous solution [183]. The DNA adsorption behavior depended much on the pore size of the mesoporous silica. Plausible models of DNA accommodation in mesopore silica channels are depicted in Figure 4.20. Inclusion of duplex DNA in mesoporous silicates with larger pores, around 3.8 nm diameter, would be accompanied by the formation of four water monolayers on the silica surface of the mesoporous inner channel (Figure 4.20A), where sufficient quantities of Si—OH groups remained after solvent extraction of the template (not by calcination). 

Keywords DNA Adsorption Materials Graphite Carbon Composite Nanotube Electrochemical sensing... 

The direct electrochemical detection of DNA was initially proposed by Palecek [8,9], who recognized the capabihty of both DNA and RNA to yield reduction and oxidation signals after being adsorbed. The DNA oxidation was shown to be strongly dependent on the DNA adsorption on the substrate it requires meticulous control of the DNA-adsorbed layer. 

The next section will be focused on the description of the most important features related to DNA adsorption strategies that have found applications in DNA electrochemical analysis. 

DNA adsorption properties were first studied using a variety of solid supports for classical analysis methods including Southern and Northern transfers, dot-blotting, colony hybridization and plaque-lifts [31,32]. Studies of the interactions between nucleic acids and nitrocellulose revealed that molecular weight, finite macromolecular conformation, ionic forces and weaker forces of attraction all play a role. DNA is retained on nitrocellulose only in... 

However, when the potential of the pretreatment of the GC exceeded -I- 1.75 V (vs SCE) or it was driven longer than 300 s in PBS (pH 5.0), the adsorption of ssDNA at the electrode was found to decrease [46], showing that different conditions for obtained GC(ox) were detrimental for the DNA adsorption and oxidation. A similar negative effect was observed when the adsorption of the DNA was performed on polished GC previously exposed to air for a given time [44]. 

GC material was widely modified with conducting (or nonconducting) polymers in order to obtain an improved surface for DNA adsorption and detection. The initial approaches were performed by the physical attachment of nylon or nitrocellulose membranes on GC electrodes [51]. As explained, these membranes were extensively used in classical DNA analysis due to their well-known adsorption properties [33]. Other approaches were performed by the direct adsorption of the polymeric film on the GC surface. Finally, polymeric films were electrochemically grown on the GC substrate. These conducting polymers are particularly promising for the adsorption, but also for inducing electrical signals obtained from DNA interactions. 

The adsorption of DNA and its derivatives on CP materials has been widely reported. CP for DNA adsorption could be successfully prepared by the... 

Besides DNA adsorption driven by a positive potential (electrostatic adsorption) DNA was also wet-adsorbed at an open circuit on a home-made polystyrene-based carbon ink [110]. This ink was prepared by a 2 3 mixture of polystyrene and graphite particles in mesitylene, and then printed on a polyester film. DNA was wef-adsorbed over the ink at 37 °C overnight. The nature of the electrode surface (graphite particles embedded in a polystyrene... 

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