Electrochemical impedance spectroscopic analysis of binding interactions between haptens and poly L- Arginine and poly L-Lysine

Abstract

Fabrication of an 11-mercaptoundecanoic acid (MUA) self-assembled monolayer (SAM) modified gold electrode in-situ functionalized with poly L-Arginine (pArg) and poly L-Lysine (pLys) is presented and described. The fabricated electrode was used for highly selective and sensitive accumulation and the determination of hapten molecules (Glycerol, Isoeugenol and Maleic anhydride) in a nanomolar concentration. Techniques like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with an external redox probe (FeCN6 (3-/4-)) were used to investigate the layer-by-layer self assembly modification on a gold electrode, monolayer structure and the ion permeation through it. For CV,Results indicated considerable decrease in current due to immobilizations of amino acid monolayers. In addition, increase in Charge Transfer Resistance (Rct) as main EIS output and Constant Phase Element (CPE) illustrated the quality and the accuracy of Layer-by-Layer (LBL) assembly of SAM monolayers on the surface of gold. EIS study showed the stable readings of Rct relating to pArg and pLys attachment, which was obtained after at least 20 min of immobilization indicating the minimum stability time for amino acid monolayer formation on the gold. In terms of haptenation, increase in Rct showed the direct relation of surface resistance and the degree of hapten sensitization (from weak to strong sensitizers). Eventually,increases in Rct values after attachment of poly l-Arginine SAM monolayer (three vs.two monolayers) illustrated more resistance on the surface of the electrode and more haptenation between probes and haptens. This study can be further used on the development of impedance-based biosensor especially for skin sensitization studies in cosmetic products.