Acrylate polymer immobilisation of enzymes

A rotating disk electrode analysis of pin-holes in polymer membrane coverings is described and the results correlated with the performance of the polymers when used as immobilisation matrices for enzymes in amperometric biosensors. The polymer family chosen for study is that of the acrylates and two preparations are considered via bulk polymerisation and emulsion polymerisation. In the latter case PVA present in the polymerisation may form ‘diffusion channels’ in the deposited film. For the bulk polymers it is found that better signal response is obtained for pin-hole rich polymers, leading to the conclusion that transport of analyte/measurand is through the pin-holes. A pin-hole free polymer can be produced by inclusion of plasticiser or producing polymers with more ‘elastic’ properties (e.g. lower Tg). However, these polymers show poor permeability to analyte/measurand. The emulsion polymers can be produced with another component, e.g. PVA which may create diffusion channels. Polymers which show pin-hole behaviour in this class have hole-diffusion properties which are different to solution and comparable to a PVA ‘solution’. This approach may provide a means of optimising both immobilisation polymer matrix and diffusion channels for a biosensor, although the underlying correlation to permeability was found to be the pin-hole population rather than the hydrophilic-hydrophobic balance.