A new highly sensitive gated ion channel biosensor for antibody detection - Setup, ion channel design, supported membranes

A new technique for direct monitoring of biochemical binding events of individual molecules was developed. Artificial gated ion channels in supported membranes of circular bolaamphiphilic lipids mixed with lipid phase modifiers were used to monitor the binding events of analyte molecules to the ion channel inducing a change of the ion concentration in a small sub membrane compartment. Ion flux or the ion concentration within the small compartment was determined electrochemically or by using fluorescent indicator dyes. Binding of the analyte to ligand modified peptide channels resulted in an on/off-response of the channel current due to channel closure or distortion. Trans-membrane permeability changes were quantified by applying a trans-membrane potential or a transient pulse of pH or ion concentration. Doubtless, the need for a direct more specific measurement in complex matrices leads to the increased interest in this form of miniaturized analytical device. Nevertheless most of the biosensors developed up to now use the biochemical processes of correlated bioanalytic assays. In bioanalytical assays where the analyte binds to an artificial membrane ligand a new strategy had to be developed. This paper presents new sensor devices using optical and electrochemical signal transduction. The biorecognitive interaction of an analyte at a ligand modified Bisgramicidin A ion channel results in a nearly digital on/off response of the channel current due to peptide channel closure or distortion. The current response of the sensor induced by analyte binding depends on an accurately positioned small ligand and on the binding of a large analyte molecule as e.g. an antibody. The trans-membrane leakage of ions is very low and highly charged ions are only able to pass the membrane through membrane channels. Sodium and potassium ions as well as protons are widely spread in biological fluids. For this reason they are utilized as mobile species which are forced to move through the ion channels by an electric field or a concentration gradient. This gradient was induced either electrochemically or by ion concentration shift. The data presented show the optimization of the setup and first studies with this new device monitoring analyte gated ion channels in supported lipid membranes on sensor chips.