Composite hydrogels containing polypyrrole as support membranes for amperometric enzyme biosensors

Conducting polymers and redox hydrogels are shown to be attractive materials for biocompatible electrodes in amperometric biosensors. We have combined electrically conducting polypyrrole (PPy) with crosslinked poly(2-hydroxyethylmethacrylate) (p-HEMA) to produce a novel composite hydrogel membrane. The high water content of these materials provides a biocompatible environment for the long-term immobilization of enzymes and a more favorable medium for the rapid movement of charge neutralizing ions. Electrode-supported composite films were prepared by UV polymerization of the hydrogel component (containing dissolved enzyme) followed immediately by electrochemical polymerization (+0.7V vs. Ag/AgCl) of the pyrrole component within the interstitial spaces of the pre-formed hydrogel network. Typical monomer compositions consisted of HEMA:TEGDA:pyrrole in an 85:10:05 vol%. (TEGDA = tetraethyleneglycol diacrylate). An optimized glucose biosensor displayed a wide linear response range of 5.0 x 10(-5) to 2.0 x 10(-2) M, a detection limit (3S(y/x)/sensitivity) of 25 muM and a response time of 35-40 seconds. The analytical recovery of glucose in serum samples ranged from 98 to 102% with mean coefficients of variation of 4.4% (within-day analyses) and 5.1% (day-to-day analyses). The optimized cholesterol and galactose biosensors also displayed wide linear response ranges (5.0 x 10(-4) - 1.5 x 10(-2) M and 1.0 x 10(-4) - 1.0 x 10(-2) M, respectively) towards their respective substrates. All three biosensors retained > 70% of initial activity after 9 months when stored desiccated in the absence of buffer. An attractive feature with all the biosensors was their ability to effectively screen the endogenous interferents ascorbic acid, uric acid, L-cysteine and acetaminophen. This characteristic, coupled with the high biocompatibility of the polymeric hydrogel composites make these materials potential candidates for in-vivo biosensors.