7, 7, 8, 8-Tetracyanoquinodimethane TCNQ , biosensors

Mediators such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) [166], hexacyanoferrate(III) [168] and CoPC [169], which have been applied to a carbon paste or ink, are reduced by the reaction with thiocholine and then reoxidised at the carbon electrode (Fig. 23.6). A second type of mediator has involved the addition of Prussian blue (ferric hex-anocyanoferrate) into an AChE and choline oxidase (ChO) bienzyme biosensor. Prussian blue mediates the reduction of hydrogen peroxide produced by the conversion of choline to betaine by ChO [170]. 

Tetracyanoquinodimethane (TCNQ) and many of its derivatives are easily reduced to anions of the type TCNQ-, which form salts with various cations. With many cations, e.g., tetrathiafulvalene cations (TTF+), and N-methyl phenazinium cations (NMP+), the TCNQ- anions form electronically conducting salts (- molecular metals, -> charge-transfer complexes) that can be used as electrodes, especially because of their electrocatalytic properties (- biosensors, -> electrocatalysis, -> molecular metals) [i,ii]. TCNQ undergoes insertion electrochemical reactions (-> insertion electrochemistry) leading to TCNQ salts [iii, iv]. Polymers... 

For example, Carlo and co-workers modified the surface of a screen-printed carbon electrode with a thin layer of perfluorinated ion-exchanger films containing 7,7,8,8-tetracyanoquinodimethane (TCNQ) as mediator. It was found that the reduced form of TCNQ was oxidized at 0.4 V vs. the pseudo-reference electrode (Ag wire). The TCNQ-based biosensors were applied to a recovery test using egg, bovine meat, milk, and honey as food matrices. No false-negative or false-positive samples were detected in the assay. 

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