Transducer in biosensors

K. Larsson, K. Kriz and D. Kriz, Magnetic transducers in biosensors and bioassays, Analusis, 27 (1999) 617-621. 

The oxygen electrode according to Clark [9] and its version modified for H2O2 indication [10] are the most widely used transducers in biosensors. The electrode potential is crucial for the selectivity of the sensor. Any electroactive substance being converted at lower potential contributes to the total current. Thus at an electrode potential of -1-600 mV for H2O2 measurement, ascorbic acid, uric acid, or paracetamol are oxidized as well. 

Potentiometric electrodes have been used as transducers in biosensors in which a thin layer containing enzymes, antibodies, or whole cells separates the electrode surface from the analyte solution and provides selective recognition properties. Thin layers containing enzymes or cells catalyze reactions that cause the localized production or consumption of the species to which the electrode responds. Antibodies, incorporated into immunosensors, have been shown to cause small but measurable signals upon antigen binding, but usually require a label (such as an enzyme) that allows catalysis of a reaction that can be followed potentiometrically [13]. 

Further utilization of amperometric transducers in biosensor for medical mass diagnostics [46],... 

Application of transition metal hexacyanoferrates for development of biosensors was first announced by our group in 1994 [118]. The goal was to substitute platinum as the most commonly used hydrogen peroxide transducer for Prussian blue-modified electrode. The enzyme glucose oxidase was immobilized on the top of the transducer in the polymer (Nation) membrane. The resulting biosensor showed advantageous characteristics of both sensitivity and selectivity in the presence of commonly tested reductants, such as ascorbate and paracetamol. 

Metal hexacyanoferrates-based biosensors were developed for analysis of glucose [11, 114, 118, 127, 147, 149, 152, 155-166], ethanol [11], D-alanine [147], oxalate [167-169], cholesterol [170, 171], glutamate [114, 119], sucrose [172], and choline [163], Among the transducers used Prussian blue undoubtedly dominates especially if one takes into account that instead of both chromium and cobalt hexacyanoferrates the activity of the transducers in publications [149, 159, 167, 168] was most probably provided by Prussian blue [117]. The sensitivity of cupric hexacyanoferrate is several orders of magnitude lower compared to Prussian blue. However, chemically synthesized... 

The applications of nanoparticles in biosensors can be classified into two categories according to their functions (1) nanoparticle-modified transducers for bioanalytical applications and (2) biomolecule-nanoparticle conjugates as labels for biosensing and bioassays. We intend to review some of the major advances and milestones in biosensor development based upon nanoparticle labels and their roles in biosensors and bioassays for nucleic acids and proteins. Moreover, we focus on some of the key fundamental properties of certain nanoparticles that make them ideal for different biosensing applications. 

The use of optical immune biosensors based on surface plasmon resonance (SPR) for the diagnostics of human and animal diseases as well as for environmental pollution monitoring, is one of prospective directions in biosensorics. The sensitivity of immune biosensors is similar to the ELIS A-method but the simphcity of obtaining results in the real time regime and the speed of the analysis are the main advantages of the biosensor approach. Performance of optical biosensors based on SPR depends on the state of the metallic surface as well as on the density, structure and the space volume of the immobilized molecules. It was demonstrated that the application of intermediate layers between the transducer surface and the sensitive biological molecules can optimize the working characteristics of the immune biosensor [7-14]. 

Nanostructured Silicon and its Application as the Transducer in Immune Biosensors... 

The simple cases where one enzyme is employed afford a limited scope of potential targets. Usually two or more enzyme reactions are coupled, as exemplified by the development of a piezoelectrically-transduced biocatalytic biosensor that couples two enzyme reactions to detect glucose [492-62-6], C6H120 > (3) (13). In this biosensor a quartz radio crystal is functionalized with the enzyme glucose-6-phosphate dehydrogenase. As shown in Figure 3, a thin film of Prussian blue [14038 43-8], C18N18Fe7, is then coated onto the crystal. 

One of the key factors in biosensor design is the immobilisation technique used to attach the biorecognition molecule to the transducer surface so as to render it in a stable and functional form. The challenge is to have a stable layer (or layers) of biorecognition molecules that do not desorb from the surface and that retain their activity. Entrapment or encapsulation techniques avoid the chemical changes that usually change the structure of the enzymes and modify their recognition capacity. 

An SPCE modified with CoPC was employed as an H202 transducer in a cholesterol biosensor fabricated by the drop-coating of ChOx, followed by a cellulose acetate membrane [50]. The resulting cholesterol biosensors were operated in stirred solutions using an applied potential of +400 mV vs. screen-printed Ag/AgCl, and displayed a linear range of 0.06-5 mM. 

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