A NOS gene electrochemical biosensor was prepared by covalently immobilizing of NOS ssDNA sequence on the mercaptoacetic acid monolayer self-assembled gold electrode with the help of N-（3-dimethylaminopropyl）-N’-ethylcarbodiimide hydrochloride（EDC）and N-hydroxysuccinimide（NHS）.By using methylene blue as the electrochemical indicator,the increase of cathodic peak current was in linear with the concentration of complementary ssDNA in the concentration range of 5.0×10-8 1.0×10-4 mol/L with the linear regression equation as ΔI pc=1.10lgc+8.25（n=8,γ=0.998 5）and the detection limit as 3.60×10-8 mol/L（3σ）.
