Two glucose-responsive polymers

In summary, the steady state and transient performance of the poly(acrylamide) hydrogel with immobilized glucose oxidase and phenol red dye (pAAm/GO/PR) demonstrates phenomena common to all polymer-based sensors and drag delivery systems. The role of the polymer in these systems is to act as a barrier to control the transport of substrates/products and this in turn controls the ultimate signal and the response time. For systems which rely upon the reaction of a substrate for example via an immobilized enzyme, the polymer controls the relative importance of the rate of substrate/analyte delivery and the rate of the reaction. In membrane systems, the thicker the polymer membrane the longer the response time due to substrate diffusion limitations as demonstrated with our pAAm/GO/PR system. However a membrane must not be so thin as to allow convective removal of the substrates before undergoing reaction, or removal of the products before detection. The steady state as well as the transient response of the pAAm/GO/ PR system was used to demonstrate these considerations with the more complicated case in which two substrates are required for the reaction. 

In devices of the first type, the conducting polymer starts in the oxidized state and is reduced as a result of the enzyme-catalyzed reaction of the substrate. This changes conductivity of the polymer, thus switching on or off the device. To reset the switch, it is necessary to connect the device to a potentiostat and reoxidize the film electrochemically (Fig. 9.14). Two devices have been reported to date, one based on poly(pyrrole)/poly(N-methylpyrrole) and responsive to NADH, the second based on poly(aniline) and responsive to glucose. In the latter case the device is switched from off to on, which appears to be advantageous, since it gives much faster response times. 

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