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

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.