Biosensors are the devices or materials that respond selectively to biological targets via a specific molecular recognition probe, and convert the biological recognition event into a sensing signal via a proper transducer. They can be directly used to detect and quantify specific analytes. The molecular recognition probe in a biosensor is normally a biomolecule or other biological material that needs to be attached to the surface of a transducer. The bioactivity of the molecular recognition probe is strongly dependent on the immobilization method. For example, the direct adsorption of an enzyme on a planar inorganic surface may cause the denaturation of the enzyme. Nanomaterials generally refer to materials with at least one of their geometric dimensions falling between 1 and 100 nm. Nanomaterials and nanodevices are much more attractive as transducers than traditional micro- and macrocounterparts. Biosensors are constructed based on the specific mechanism that transduces the biological binding/interaction events into physical signals.