Biosensors potentiometric

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

Few potentiometric biosensors are commercially available. As shown in Figures 11.16 and 11.17, however, available ion-selective and gas-sensing electrodes may be easily converted into biosensors. Several representative examples are described in Table 11.5, and additional examples can be found in several reviews listed in the suggested readings at the end of the chapter. 

Schematic diagram of an enzyme-based potentiometric biosensor for urea in which urease is trapped between two membranes.

The following set of suggested experiments describes the preparation of solid-state and liquid ion-exchange ion-selective electrodes, as well as potentiometric biosensors. 

Directions for preparing a potentiometric biosensor for penicillin are provided in this experiment. The enzyme penicillinase is immobilized in a polyacrylamide polymer formed on the surface of a glass pH electrode. The electrode shows a linear response to penicillin G over a concentration range of 10 M to 10 M. 

The use of additional membranes, which selectively convert nonionic analytes into ionic species that can be determined via ISEs is another common approach. An abundance of ingenious designs make use of biocatalysts for the development of potentiometric biosensors. Much of the earlier designs have made use of enzymes as the molecular recognition element. The products that are associated with such enzyme-catalyzed reactions can be readily monitored with the potentiometric transducer by coating the traditional electrodes with the enzyme. 

FERNANDES J c B, kubota L T and de Oliveira N (1999), Potentiometric biosensor for L-ascorbic acid based on ascorbate oxidase of natural source immobilized on ethylene-vinylacetate membrane , Anal Chim Acta, 385, 3-12. 

Composite potentiometric sensors involve systems based on ion-selective electrodes separated from the test solution by another membrane that either selectively separates a certain component of the analyte or modifies this component by a suitable reaction. This group includes gas probes, enzyme electrodes and other biosensors. Gas probes are discussed in this section and chapter 8 is devoted to potentiometric biosensors. 

L.B. WINGARD Jr. and J. CASTNER, "Potentiometric biosensors based on redox electrodes", in "Biosensors Fundamentals and Applications", Oxford University Press, Oxford, 1987, p. 153. 

Ercole, C., Del Gallo, M., Mosiello, L., Baccella, S., and Lepidi, A. (2003). Escherichia coli detection in vegetable food by a potentiometric biosensor. Sens. Actmtors B Chem. 91, 163-168. 

In addition, such redox-active organometallic dendrimers are interesting materials with which to modify electrode surfaces. Applications of these dendrimer modified electrodes in the fields of amperometric and potentiometric biosensors, molecular recognition, as well as in electrocatalysis and photoelectrochemistry, clearly represent interesting areas of future research. 

Thust M, Schoening MJ, Erohnhoff S et al (1996) Porous silicon as a substrate material for potentiometric biosensors. Meas Sci Technol N7 26-29... 

H. Me Connell, J. Parce and D. Hafeman, Light addressable potentiometric biosensor, J. Electrochem. Soc., 134(8B) (1987) C523. 

J.C. Fernando, K.R. Rogers, N.A. Anis, J.J. Valdes, R.G. Thompson, A.T. Eldefrawi andM.E. Eldefrawi, Rapid detection of anticholinesterase insecticides by a reusable light addressable potentiometric biosensor, J. Agrie. Food Chem., 41(3) (1993) 511-516. 

L. Mosiello, C. Laconi, M. Del Gallo, C. Ercole and A. Lepidi, Development of a monoclonal antibody based potentiometric biosensor for terbuthylazine detection, Sens. Actuators B Chem., 95(1-3) (2003) 315-320. 

M. Adami, M. Sartore, A. Rapallo and C. Nicolini, Possible developments of a potentiometric biosensor, Sens. Actuators B Chem., 7(1-3) (1992) 343-346. 

A. Ciucu, C. Ciucu and R.B. Baldwin, Organic phase potentiometric biosensor for detection of pesticides, Roum. Biotechnol. Lett., 7 (2002) 625-630. 

A.L. Ghindilis, T.G. Morzunova, A.V. Barmin and I.N. Kurochkin, Potentiometric biosensors for cholinesterase inhibitor analysis based on mediatorless bioelectrocatalysis, Biosens. Bioelectron, 11 (1996) 873-880. 

The potentiometric biosensor is a combination of an ion-selective electrode (ISE) base sensor with a vegetable tissue (the source of enzyme), which provides a highly selective and sensitive method for the determination of a given substrate. Advantages of such potentiometric biosensors are simplicity of instrumentation (only a pH meter is needed),... 

The final factor that affects the speed of the response is the electrode sensor itself and how fast it reaches a potential (potentiometric biosensor) or current (amperometric/voltammetric biosensor) proportional to the concentration of the products or reactants it has detected. A consideration of each of these factors affecting the response time is discussed in detail elsewhere [59,60]. 

Fig. 17.11. (a) Potentiometric biosensor based on pH electrode (b) Poten-tiometric biosensor based on gas electrode (c) Oxygen electrode determination of oxygen (d) Oxygen electrode determination of hydrogen peroxide (from Ref. 

Ion selective electrodes can also be used as transducers in potentiometric biosensors. An example is a biosensor for urea (blood urea nitrogen, BUN) based on a polymembrane ISE (vinyl chloride) for ammonium ion (Figure 4-14). The enzyme urease is immobilized at the surface of the ammonium selective ISE based on the antibiotic nonactin (see structure of ionophore in Figure 4-3), and catalyzes the hydrolysis of urea to NH3 and CO2. 

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