Electrochemical biosensor, molecular

A DNA-electrochemical biosensor is formed by a DNA film, which constitutes the molecular recognition element (the probe), directly immobilized on the electrochemical transducer. The performance, sensitivity and reliability of the DNA biosensor and the electrochemical response are dictated by the DNA immobilization procedure. The DNA biophysical properties, such as flexibility, and DNA-drug interactions, are influenced... 

Coupling between a biologically catalyzed reaction and an electrochemical reaction, referred to as bioelectrocatalysis, is the constructional principle for enzyme-based electrochemical biosensors. This means that the flow of electrons from a donor through the enzyme to an acceptor must reach the electrode in order for the corresponding current to be detected. In case a direct electron transfer between the active site of an enzjane and an electrode is not possible, a small molecular redox active species, e.g. hydrophobic ferrocene, meldola blue and menadione as well as hydrophilic ferricyanide, can be used as an electron transfer mediator. This means that the electrons from the active site of the enzyme reduce the mediator molecule, which, in turn, can diffuse to the electrode, where it donates the electrons upon oxidation. When these mediator molecules are employed for coupling of an enzymatic redox reaction to an electrode at a constant potential, the resulting application can be referred to as mediated amperometry or mediated bioelectrocatalysis. 

The immobilization of a macromolecular biomolecule on conductive surfaces is the subject of increasing research efforts for the development of electrochemical biosensors and biofuel cells. The main motivation for the functionalization of the surface of a conventional electrode is to confer molecular recognition properties or selective catalytic activity to this electrode. 

Rai, V., Nyine, Y.T., Hapuarachchi, H.C. et al. (2012) Electrochemically amplified molecular beacon biosensor for ultrasensitive DNA sequence-specific detection of Legionella sp. Biosens. Bioelectron., 32 (1), 133-140. 

As well known, biosensors are small devices that provide selective analysis by monitoring biochemical molecular recognition. They are specific, fast, portable, and economical systems. On the other hand, utilization of electrochemistry brings practicality, sensitivity, accuracy, speed, and low cost to biosensor systems. POC technology needs practicality and portability together with sensitivity and accuracy. In this sense, electrochanical biosensors have the potential to become the core of POC technology. The further parts of this chapter will focus on definition and types of electrochemical biosensors, their potentials as POC systems, and their applications in medical areas. 

HlavataL, Bankova K, Vyskocil V, Labuda J (2012) Evaluation of damage to DNA induced by UV-C radiation and chemical agents using electrochemical biosensor based on low molecular weight DNA and screen-printed carbon electrode. Electrochim Acta 71 134-139. doi 10.1016/j.electacta.2012.03.119... 

There are three main functional steps of an electrochemical biosensor, as illustrated in Fig. 11.1. The first step is the molecular recognition, which is ideally specific to the target analyte. The second step is the signal transduction the conversion of the molecular interactimi into a measurable electrical signal, such as current, potential, or conductivity. The final step of the sensing procedure is converting the measured signal into a readable output. 

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

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