Biosensor surface characterisation: confirming multilayer immobilisation, determining coverage of the biospecies and establishing detection limits

Sensor behaviour is strongly influenced by the surface geometry and morphology of the immobilised biolayer. In a non-amplification system the detection limits are primarily determined by the number of active biomolecules immobilised on the transducer. It is critical to be able to measure this number in a reliable and reproducible manner for sensor characterisation. Without this information, sensor to sensor calibration cannot be performed and the system detection limits are not known. A routinely used immunological assay, enzyme-linked immunosorbent assay (ELISA), can be modified and used to detect the total number of molecules and the number of active molecules immobilised on a variety of surfaces. In conjunction with other surface techniques, scanning electron microscopy (SEM) and ellipsometry, the modified ELISA technique is a useful analysis tool for biosensor characterisation.