Improved adsorption of choline oxidase on a polyelectrolyteLBL film in the presence of iodide anions

Abstract

This study describes the effects of F⁻, Cl⁻, Br⁻, and I⁻ anions on the sensitivity of a biosensor assembled via layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA) and choline oxidase (ChO) on the surface of a graphite electrode coated with MnO₂. A four-fold increase in sensitivity of the MnO₂/PDDA_KHal/ChO biosensor was observed when the adsorption of the PDDA layer was carried out from the solution containing I⁻ in a narrow range of concentrations (20–30 mM). According to AFM and SEM data, spatial distribution of the enzyme and gold nanoparticles (AuNPs) on the surface varied with the conditions of PDDA adsorption. A fine-grain film was observed when PDDA was adsorbed from the solution containing Cl⁻, whereas association of ChO or AuNPs into larger domains took place in the case of I⁻ solution. Absorption spectra of AuNPs adsorbed on a PDDA_KI film evidenced aggregate formation as well. A schematic representation of the enzyme layer assembly was proposed for different ionic conditions of the polyelectrolyte pre-adsorption.