Amperometric flow-through biosensors

A biological compound (an enzyme, usually) intended to improve the response of an electrode can be incorporated into it in two ways, namely (a) by altering the sensing surface in order to accommodate the biocatalysts [i.e. by constructing a (bio)chemically modified electrode] and (h) by using a membrane place in front of the surface electrode in order to trap the enzyme. The enzyme can be used in isolation (most often in a commercially available form) or be part of a tissue material or bacterial cells. 

Most of the amperometric flow-through biosensors based on commercially available enzymes are employed to measure consumed or released oxygen by using a Clark electrode or a solid-state electrode to monitor the hydrogen peroxide formed or an enzymatically reduced acceptor. 

Glucose oxidase, one of the most widely used enzymes for constructing biosensors, was employed by Matuscewski and Trojanowicz to develop a biosensor based on a mixture of graphite powder, silicone oil and the biocatalyst. The paste thus obtained was placed in a slot of the PTFE end 

Many biosensors rely on mediators to act in the electrode step of the detection process. Such mediators are used both as film coats over the sensor and as carrier solutions — which obviously results in more complicated and expensive determinations. Biosensor mediators are usually organic compounds [82,83] or, to a lesser extent, inorganic substances [84], depending on the particular enzyme used and species to be determined. 

A C felt sensor coated with a glucose oxidase monolayer was used in an FI manifold in the presence of dissolved potassium hexacyanoferrate as mediator for the on-line determination of interferents [89]. 

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Glucose and lactate were simultaneously monitored by Wei Min et al. [191] during the fermentation of Lactococcus lactis. They made use of a microdialysis probe connected to a dual flow-through cell in which two amperometric biosensors were located. The biosensors were based on the co-immobilization of the respective oxidase enzymes together with HRP in a carbon paste matrix. Both analytes were monitored on-hne for about 14 h in a very complex aqueous two-phase fermentation process, and the results were in good agreement with independent ofiF-line HPLC measurements. 

Redox polymers have been combined with conducting polymers to fabricate amperometric biosensors for glucose. Rohde et al. [57] described a reagentless, flow-through glucose biosensor by codeposition of glucose oxidase with glutaraldehyde and the osmium-based redox polymer synthesized by Heller... 

Lates, V., J.-L. Marty, and I. C. Popescu. 2011. Determination of antioxidant capacity by using xanthine oxidase bioreactor coupled with flow-through H2O2 amperometric biosensor. Electroanalysis 23(3) 728-736. 

Acetylcholinesterase is by far the most widely used enzyme in the preparation of biosensors for determining pesticides, both because organophosphorus insecticides and carbamates represent over half of the entire insecticide market and because the acetylcholinesterase commercially available has a high degree of purity and specificity of action and may be paired with many transducers (potentiometric, amperometric) in both flow and nonflow systems [62]. The specific tendency of organophosphorus pesticides and carbamates to inhibit acetylcholinesterase has been exploited for the purpose of determining these compounds, which are first separated by means of HPLC, then detected through a post-column reaction with immobilized acetylcholinesterase [63]. 

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