Nucleic acids electrochemical detection

Guanine, with a formal potential at pH 7 of 1.3 V vs. normal hydrogen electrode (NHE) (1.06 V vs. saturated calomel electrode (SCE)), is the most easily oxidized of the four DNA bases/331 The other bases have formal potentials up to 0.5 V more positive. Detecting nucleic acids by electrochemical oxidation depends on structure, with double-stranded (ds) DNA giving only trace oxidation peaks at best and single-stranded (ss) DNA giving irreversible oxidation peaks at about 1.0-1.2 V vs. SCE on carbon electrodes. 

The topics discussed in the book include electrochemical detection of DNA hybridization based on latex/gold nanoparticles and nanotubes nanomaterial-based electrochemical DNA detection electrochemical detection of microorganism-based DNA biosensor gold nanoparticle-based electrochemical DNA biosensors electrochemical detection of the aptamer-target interaction nanoparticle-induced catalysis for DNA biosensing basic terms regarding electrochemical DNA (nucleic acids) biosensors screen-printed electrodes for electrochemical DNA detection application of field-effect transistors to label-free electrical DNA biosensor arrays and electrochemical detection of nucleic acids using branched DNA amplifiers. 

Kafil, J. B., Cheng, H.-Y., and Last, T. A., Quantitation of nucleic acids at the picogram level using high-performance liquid chromatography with electrochemical detection, Anal. Chem., 58, 285, 1986. 

The unique practical properties of adsorption have promoted its extensive use in genetic analysis. The disadvantages of adsorption with respect to covalent immobihzation are mainly that (1) nucleic acids may be readily desorbed from the substrate, and (2) base moieties may be unavailable for hybridization if they are bonded to the substrate in multiple sites [34]. However, the electrochemical detection strategy based on the intrinsic oxidation of DNA requires the DNA to be adsorbed in close contact with the electrochemical substrate by multi-point attachment. This multi-site attachment of DNA can be thus detrimental for its hybridization but is crucial for the detection based on its oxidation signals. 

The observation of currents attributable to the faradaic electrochemistry of nucleic acids was pioneered by Palecek and coworkers who studied DNA adsorbed on mercury or carbon electrodes [13]. The signals detected by Palecek were attributable to oxidation of the purines, which produced signals indicative of irreversible processes involving adsorbed bases. These reactions were used as a basis for electrochemical analysis of DNA. Kuhr and coworkers later showed that similar strategies could be developed for analysis of nucleic acids via oxidation of sugars at copper electrodes [14-16]. 

Currently, there is a need for high-throughput determination of nucleic acid sequences. At present, detection systems most commonly employ fluorescence-based methods. However, wide spread applications of such methods are limited by low speed, high cost, size, and number of incubations steps, among other factors. Application of electrochemical methods in affinity DNA sensors presents likely a promising alternative, allowing miniaturization and cost reduction, and potentially allowing application in point-of-care assays. 

Figure 12.19 Electrochemical detection of thrombin by the interaction between a nucleic acid and a redox-active oligothiophene polyelectrolyte. The electrical contact between the polyelectrolyte and the electrode by means of the aptamer/thrombin complex is blocked. Parts Reprinted with permission from Ref. 66b. Copyright Wiley-VCH Verlag GmbH Co.

Amplified electrochemical detection of DNA in monolayer assemblies was accomplished by the conjugation of bioelectrocatalytic transformations to the DNA recognition events. This was exemplified with the amplified electrochemical analysis of M13 phage DNA (Fig. 12.20a).75 A capturing nucleic acid, (20), complementary to... 

We further addressed the use of the nucleic acids as biopolymers for the formation of supramolecular structures that enable the electronic or electrochemical detection of DNA. Specifically, we discussed the use of aptamer/low-molecular-weight molecules or aptamer/protein supramolecular complexes for the electrical analysis of the guest substrates in these complexes. Also, nucleic acid-NPs hybrid systems hold a great promise as sensing matrices for the electrical detection of DNA in composite three-dimensional assemblies. While sensitive and selective electrochemical sensors for DNA were fabricated, the integration of these sensor configurations in array formats (DNA chips) for the multiplexed analysis of many DNAs can also be envisaged. 

An overview on the genosensor technologies for detection of nucleic acids (NA) immobilized onto different transducers by adsorption, cross-linking, complexation and covalent attachment is briefly summarized in Table 19.1. The applications of electrochemical genosensor technology are discussed in the following section. 

The electrochemical behaviour and the adsorption of nucleic acid molecules and DNA constituents have been extensively studied over recent decades [1-6]. Electrochemical studies demonstrated that all DNA bases can be electrochemically oxidized on carbon electrodes [7-13], following a pH-dependent mechanism. The purines, guanine (G) and adenine (A), are oxidized at much lower positive potentials than the pyrimidines, cytosine (C) and thymine (T), the oxidation of which occurs only at very high positive potentials near the potential corresponding to oxygen evolution, and consequently are more difficult to detect. Also, for the same concentrations, the oxidation currents observed for pyrimidine bases are much smaller than those observed for the purine bases. Consequently, the electrochemical detection of oxidative changes occurring in DNA has been based on the detection of purine base oxidation peaks or of the major... 

Data presented here demonstrate the potential applicability of SPCEs genosensors in the diagnosis of a human infectious pulmonary disease. These electrochemical genosensors are stable and sensitive devices for the detection of specific nucleic acid fragments. Moreover,... 

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