The optimised biosensor required only 5 U of FDH and kept the 80% of its initial sensitivity after 4 months. During this time, the biosensor showed a detection limit for fructose of 1 lM, a large linear range between 0.1 and 5 mM, a high sensitivity (1.95 lAcm 2 mM), good reproducibility (RSD = 2.1%) and a fast response time (4 s).