Capacitive Immunosensors – Capacitive Immunosensors – A Tool for Detection Where Sensitivity of Conventional ELISA is Not Sufficient

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SELECTBIO

Bo Mattiasson, Professor, Department of Biotechnology, Lund University

Abstract
A capacitive immunosensor has been developed. The electrode consists of a gold surface that is well insulated either by a self-assembled monolayer of alkylthiol or electropolymerized tyramin. Antibodies or other binding reagents are immobilized on this layer. When binding of an antigen takes place, it is possible to register a change in capacitance upon a potential pulse given to the sensor chip. This technology offers a sensitivity that is far above that of conventional ELISAs. Traditionally, capacitive biosensors have been unstable and thereby difficult to use. However, by proper stabilization of the system, capacitive measurements are now stable enough to become interesting routine instruments for sensitive analyses. The sensors in used in connection with a flow-injection system which also contributed to improve the analytical outcome. When analyzing proteins, it is possible to detect and quantify proteins in the concentration range 10-15 – 10-19 M. This extreme sensitivity is ascribed to the detection principle and also the very high concentration of antibodies on the electrode surface. Bacterial toxins (cholera, entero- and endotoxins etc.) have been successfully quantified using this highly sensitive detection principle (Loyprasert et al, 2010). Furthermore, quantification of host cell proteins from biotech preparations of transgenic proteins is another challenging application that has been addressed (Teeparuksapun et al, published online). Likewise, the p24 protein from the capsid of the HIV-virus has been quantified both in buffer solutions and in serum samples with high sensitivity (Teeparuksapun et al, 2010).