Biosensors genosensors

Many DNA-based biosensors (genosensors) are based on the ability of complementary nucleic acid strands to selectively form hybrid complexes. The complementary strands anneal to one another in a Watson-Crick manner of base pairing. Hybridization methods used today, such as microhtre plates or gel-based methods, are usually quite slow, requiring hours to days to produce reliable results, as described by Keller and Manak [10]. Biosensors offer a promising alternative for much faster hybridization assays. 

Electrochemical DNA biosensors (genosensors) developing for the detection of compound-DNA interactions are very competitive devices for the aim of detection time and cost, with the possibility... 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

A genosensor, or gene-based biosensor/DNA biosensor, normally employs immobilized DNA probes as the recognition element and measures specific binding processes such as the formation of DNA-DNA and DNA-RNA hybrids, and the interactions between proteins or ligand molecules and DNA at the sensor surface [5]. 

Compared to genosensors based on GEC, the novelty of this approach is in part attributed to the simplicity of its design, combining the hybridization and the immobilization of DNA in one analytical step. The optimum time for the one-step immobilization/hybridization procedure was found to be 60 min [66]. The proposed DNA biosensor design has proven to be successful in using a simple bulk modification step, hence, overcoming the complicated pre-treatment steps associated with other DNA biosensor designs. Additionally, the use of a one-step immobilization and hybridization procedure reduces the experimental time. Stability studies conducted demonstrate the capability of the same electrode to be used for a 12-week period [66]. 

As we have already mentioned, various methods of immobilization of aptamers onto a solid support are used. In principle these methods are similar to those applied previously for immobilization of single- or double-stranded DNA in genosensors or DNA biosensors for detection of DNA damage (see Pividori et al. [33] for review). The methods of... 

The development of electrochemical genosensors and immunosen-sors based on labelling with NPs has registered an important growth, principally for clinical and environmental applications. The electrochemical detection of NP labels in affinity biosensors using stripping methods allows the detailed study of DNA hybridisation as well as immunoreactions with interest in genosensor or immunosensor applications. 

Wide-scale genetic testing requires the development of easy to use, fast, inexpensive, and miniaturized analytical devices. Hybridization DNA biosensors (also called genosensors) offer a promising alternative to traditional methods based on either direct sequencing or DNA hybridization, commonly too slow and labor intensive. 

Lucarelli et al. describe a disposable indicator-free screen-printed genosensor applied to the detection of apoE sequences in PCR samples [26]. The biosensor format involved the immobilization of an inosine-modified (guanine-free) probe onto a SPE transducer and the detection of the duplex formation in connection with the square-wave voltammetric measurement of the guanine oxidation peak of the target sequence. 

A very broad research activity in recent years is focused on investigation of possibilities of applications of nucleic acids for biosensing, especially DNA. As DNAs in organisms function as carrier of genetic information, for biosensors employing DNA as molecular recognition element a name genosensors appears recently in analytical literature. 

Among numerous reported applications of genosensors for DNA hybridization as few examples, one can refer to a disposable DNA sensor for detection of hepatitis B virus genome DNA,145 biosensor systems for homeland security using DNA microarrays,146 and DNA electrochemical biosensor with conducting polymer film and nanocomposite as matrices for detection of HIV DNA sequences.147... 

For enzyme-based biosensors the mode of detection is based on the catalytic activity and/or binding capacity. Because of the protein nature of almost all enzymes, the catalytic activity depends on the conformation. Exceptions are catalytic ribonucleic acids called DNA biosensors or genosensors. DNA fragments are used as probes for detecting low concentrations of DNA in large samples (see also Part I, Chapters 2 and 3). Because of the highly diluted DNA concentration, microelectromechanical systems which are able of performing PCRs are employed. 

One of the most applicable metal nanoparticles is gold nanoparticles which have been used in different fields. These applications are enzymatic biosensors based on gold nanoparticles and their applications in genosensors, immunosen-sors, and electrocatalytic chemosensors (Fredy, 2008). 

DNA immobilization step plays the most important role in determining the performance of an electrochemical genosensor (DNA-based biosensor) [15]. Control of the DNA binding surface in terms of surface orientation and coverage is essential for the sensitive monitoring of DNA-DNA and compound-DNA interactions by electrochemistry. 

Amperometric or voltammetric biosensors typically rely on an enzyme system that catalyt-ically converts electrochemically non-active analytes into products that can be oxidized or reduced at a working electrode. Although these devices are the most commonly reported class of biosensors, they tend to have a small dynamic range due to saturation kinetics of the enzyme, and a large overpotential is required for oxidation of the analyte this may lead to oxidation of interfering compounds as well (e.g., ascorbate in the detection of hydrogen peroxide). In addition to the use in enzyme-based biosensors, amperometric transducers have also been used to measure enzyme-labelled tracers for affinity-based biosensor (mainly immunosensors and genosensors). Enzymes which are commonly used for this purpose include horseradish peroxidase (HRP) [17] and alkaline phosphatase (AP) [18,19,21]. 

The label-free DNA biosensor approach comprises the direct detection of changes of some electrical parameter from the hybridisation event. The first reported use of this kind of genosensor was by Wang et al In this work, the hybridisation event was detected by monitoring the decrease of the guanine peak of an immobilised DNA probe. 

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