Analytica Chimica Acta 461 (2002) 57–64 Entrapment of glucose oxidase in non-porous poly(vinyl chloride) Subrayal M. Reddy a,∗ , Pankaj Vadgama b a School of Biomedical and Life Sciences, Centre for Clinical Science and Measurement, University of Surrey, Guildford, Surrey GU2 7XH, UK b Queen Mary and Westfield College, IRC in Biomedical Materials, Mile End Road, London E1 4NS, UK Received 14 November 2001; received in revised form 12 March 2002; accepted 19 March 2002 Abstract 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 H 2 O 2 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 H 2 O 2 on the electrode side with less permeating through the acidified membrane into bulk solution. The results were compared against using variously plasticised PVC (but no enzyme entrapped) as an outer membrane of a classical dual-membrane glucose enzyme electrode construct. In the latter case, the enzyme was chemically crosslinked between the membranes using glutaraldehyde. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Glucose oxidase; Enzyme electrode; PVC; Entrapment; Amperometric; Biosensor 1. Introduction Use of support matrices for immobilisation of en- zymes is now common [1,2]. The typical characteris- tics of the support matrix include porosity (for protein binding) and hydrophilicity to promote the enzymatic reaction under heterogeneous and water swelling con- ditions. Collagen and polyacrylamide supports have for example seen widespread use. Poly(vinyl chloride) (PVC) is hydrophobic in nature and therefore would ∗ Corresponding author. E-mail address: s.reddy@surrey.ac.uk (S.M. Reddy). appear to be unsuitable for use as a support matrix for immobilised enzymes. Hirose et al. [3] reported on the applicability of “wet” PVC membranes. This porous wet PVC membrane was distinguished from other porous membranes by the presence of water in minute pores [4]. The membranes were shown to be permeable to low molecular weight solutes (such as urea, glycine and glucose). The characteristic porous structure of the wet PVC membrane was found to play an important role in the adsorption of proteins and enzymes despite the hydrophobicity of PVC. Hirose et al. [5] also demonstrated the use of glucose oxidase (GOD) adsorbed to a polyvinylchloride membrane as 0003-2670/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0003-2670(02)00246-5