Entrapment of glucose oxidase in non-porous poly(vinyl chloride) Original Research Article

We have used solvent casting techniques to immobilise glucose oxidase (GOD) within unplasticised and plasticised poly(vinyl chloride) (PVC) matrices. The plasticisers studied were the cationic surfactant, tricaprylmethylammonium chloride (Aliquat 336s), the anionic surfactant bis(2-ethylhexyl) hydrogenphosphate (BEP) and the lipid, isopropylmyristate (IPM). The activity of the enzyme-membrane was tested by amperometric electrode. Changes in enzyme-membrane electrode response are rationalised on the basis of membrane permselective properties. The Aliquat and IPM modified PVC membranes gave amplified signals due to better retention and subsequent concentration of the H2O2 signal species. Effectively, less was being lost to the bulk solution. In the case of the BEP-modified membrane, while there was a linear step change in response up to 50 mM, at higher concentrations, responses did not reach steady-state; they were characterised by an upward drift in response of 0.050 nA/min. This characteristic is thought to be due to a build up of gluconic acid resulting in a pH reduction in the membrane microenvironment and hydrogen bonding between neighbouring BEP molecules. Under these conditions, we have previously shown that the membrane permeability to hydrophilic species is attenuated and it is tentatively suggested that the upward drift due to the build up of H2O2 on the electrode side with less permeating through the acidified membrane into bulk solution.