Polypyrrole/anthraquinone-2-sulfonate

Matsue et al. [27] were the first to explore an enzyme-based OECT biosensor. They used Diaphorase as the entrapped enzyme in a polypyrrole transducing layer for the detection of NADH via a redox mediator (the sodium salt of anthraquinone-2-sulfonic acid). The net result was the conversion of polypyrrole from its conducting state to its insulating state in the presence of NADH. The device showed a response time of 15--20 min in the presence of NADH. Later Nishizawa et al. [26] exploited the pH sensitivity of the polypyrrole film for the design and fabrication of OECT sensors for pH and for pencillin. The Penicillinase enzyme was entrapped in a membrane which was coated with a polypyrrole film, in which a decrease in pH was observed in the presence of penicillin due to the hydrolysis of penicillin by Penicillinase. 

Kaynak and coworkers [82,128] later reported on the effect of different dopant anions incorporated in the polypyrrole-coated textiles on the heat generation of these materials. The polypyrrole layer was deposited onto a polyester/Lycra fabric using the in situ polymerization approach and was doped with anthraquinone-2-sulfonate, naphthalene-2-sulfonate, p-toluenesulfonate, or perchlorate. At an applied voltage of 24 V, the polypyrrole-coated fabrics, from all the four different dopant systems showed an increase in temperature with the anthraquinone-2-sulfonate-doped polypyrrole coating the most effective heat generator (AT 20°C) whereas the sodium perchlorate dopant system was the least effective (AT 3°C). The power density per unit area achieved in the anthraquinone-2-sulfonate-doped polypyrrole-coated fabric was 430 W/m, 200 W/m for naphthalene-2-sulfonate, 150 W/m for p-toluenesulfonate, and 55 W/m for perchlorate, respectively. 

Several other groups have since published studies involving the stability of polypyrrole and polypyrrole-coated textiles. A plot produced from data obtained at Milliken Research Corporation that displays the resistance as a function of time at several different temperatures for an anthraquinone-2-sulfonic acid doped polypyrrole-coated textile is shown in Fig. 35.8. Similar results were obtained by Truong and coworkers [82,831 and Thieblemont and coworkers [ 16,841. Contrary to the earlier reports, these studies concluded that the kinetic of polypyrrole degradation are not first-order but follow a diffusion-controlled curve similar to a Frickian sorption plot. 

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