A non-covalent method of immobilisation exploits the high affinity proteins such as avidin, streptavidin and neutravidin have for biotin. This strong, rapidly forming non-covalent interaction is typically unaffected by pH, temperature or organic solvents. Biotin is bicyclic with a carboxylic acid group which can be functionalised to graft to the modified electrode surface. By functionalising the carboxyl group, the bicyclic ring remains intact for affinity binding. Typical biotin functionalisation includes NHS ester, or maleimide. As avidin, streptavidin and neutravidin can each bind four biotin molecules, a second biotin molecule can be conjugated to the bioreceptor. Immobilisation occurs through a biotin-avidin-biotin interaction.