The chitosan with three-dimensional porous structure greatly increased the effective electrode surface for loading of platinum nanoparticles and promoted efficient electron transfer. The resulting biosensor had a response time (within 5 s) and a linear response from 6 mu M to 4.2 mM glucose with a detection limit of 2 mu M (S/N = 3). Moreover, the methodology can be applied for the immobilization of other enzymes.