Abstract: In this article, we describe the use of pH- responsive hydrogels as matrices for the immobilization of two enzymes, glucose oxidase (GOx) and glutamate oxidase (GlutOx). Spherical hydrogel beads were prepared by inverse suspension polymerization and the enzymes were immobilized by either physical entrapment or covalent immobilization within or on the hydrogel surface. Packed-bed bioreactors were prepared containing the bioactive hydrogels and these incorporated into flow injection (FI) systems for the quantitation of glucose and monosodium glutamate (MSG) respectively. The FI amperometric detector comprised a microfabricated interdigitated array within a thin-layer flow cell. For the FI manifold incorporating immobilized GOx, glucose response curves were found to be linear over the concentration range 1.8-280 mg dL-1 (0.1-15.5 mM) with a detection limit of 1.4 mg dL-1 (0.08 mM). Up to 20 samples can be manually analyzed per hour, with the hydrogel-GOx bioreactor exhibiting good within-day (0.19%) precision. The optimized FI manifold for MSG quantitation yielded a linear response range of up to 135 mg dL-1 (8 mM) with a detection limit of 3.38 mg dL-1 (0.2 mM) and a throughput of 30 samples h-1. Analysis of commercially produced soup samples gave a within-day precision of 3.6%. Bioreactors containing these two physically entrapped enzymes retained > 60% of their initial activities after a storage period of up to 1 year.

Abstract: The present study reports on the use of p(2-hydroxyethyl methacrylate) (pHEMA) in which polypyrrole and various oxidoreductase enzymes were physically entrapped to function as a viable matrix for the construction of clinically important amperometric biosensors. Glucose oxidase. cholesterol oxidase and galactose oxidase biosensors were constructed. Electrode-supported hydrogel films were prepared by UV polymerization of the HEMA component (containing the 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. The optimized glucose oxidase biosensor displayed a wide linear glucose response range (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 s. The analytical recovery of glucose in serum samples ranged from 98 to 102% with mean coefficients of variation of 4.4% (within-day analyzes) and 5.1% (day-to-day analyzes). All three sensors displayed good stabilities when stored desiccated in the absence of buffer (> 9 months). (C) 2002 Elsevier Science B.V. All rights reserved.