Gas sensors and biosensors are hot topics in research in recent years. Graphene/ZnO/p-type silicon multiple heterojunctions is the main structure used in this work to serve as biosensors. By decorating uricase on graphene, uricase would conduct chemical reaction. Different concentration of uric acid would produce different number of chemical products with different reaction rate. The Fermi level would be changed when carriers were doped in graphene, which would result in band bending, and the measured electrical signal would be changed. Second part of this research is about patterned graphene heterojunctions. When uricase attaches on patterned graphene, we try to find out the relationship between different size of holes and sensitivity on the detection of uric acid.