Graphene,a monolayer of carbon atoms compacted into a tw o-dimensional honeycomb crystal structure,has attracted tremendous attention in recent years,because of its unique electronic,thermal,and mechanical properties.Here,single and few layers graphene films were synthesized by chemical vapor deposition on copper foils under ambient pressure.The resulting graphene films were investigated by AFM,STM and Raman spectroscopy.Based on the CVD grown graphene films,the liq uid gate field-effect transistors were fabrica ted and the electrical detections of DNA,cryptosporidium parvum oocysts,glucose,and so on,were realized.The stud ies indicate graphene based field-effect transistors are promising candidates for the development of nanoelectronic biosensors.