Effect of buried potential barrier in label-less electrochemical immunodetection of glutathione and glutathione-capped gold nanoparticles

The influence of potential barriers, introduced to the immunoglobulin-based sensory films, on voltammetric signals of a redox ion probe has been investigated. Films with positive and negative barriers have been examined by depositing charged self-assembled thiol monolayers as the basal layers of a sensory film. The studies performed with monoclonal anti-glutathione antibody-based sensors using ferricyanide ion probe have shown stronger sensor response to the layer components, as well as to the glutathione-capped gold nanoparticles acting as the antigen, for films with positive potential barrier buried deep in the film than for negative barrier films. The larger changes in differential resistance, peak separation and peak heights observed for films with positive barrier have been attributed to different depth and width of the charge distributions in these films. A buried positive barrier with narrow charge distribution width provides the best conditions for film stability and prevents fouling (less ion-exchanges with the medium). This conclusion has been confirmed by calculations of the electric field distribution and potential profiles in immunosensing films performed by numerical integration of Poisson equation for Gaussian distributions of fixed charges of covalently bound components. The proposed fixed-charge model can aid in rapid evaluation of sensory films in sensor development work. The implications of potential barriers in sensory film design are discussed.