Micro-cylinder biosensors for phenol and catechol based on layer-by-layer immobilization of tyrosinase on latex particles: Theory and experiment

Microelectrode sensors for phenol and catechol are described, based on the sequential immobilization of polystyrene sulphonate, polyallylamine, tyrosinase and polyallylamine again, onto micrometer scale latex spheres, followed by the adsorption of the spheres onto electrochemically pretreated carbon fibres. The steady state responses of the fibres are analyzed in terms of a cylindrical diffusion - kinetic model. It is deduced that the adsorbed latex particles provide a relatively open film structure, resulting in a diffusion coefficient only one order of magnitude lower than the solution value, and that at minimum 2-3% of the immobilized enzyme is catalytically active. The optimised sensors exhibit linear ranges to phenol and catechol of 7-56.5 μM and 2-19.7 μM respectively, with sensitivities of 0.15 A M^-1 cm^-2 and 1.72 A M^-1 cm^-2 respectively. The limiting factor to sensor stability is desorption of latex from the fibres.