In target DNA detection, as shown Fig. 1, when the probe DNA of DFNP is under stem-loop state, a comparatively huge bulk of Au nanoparticle and the loop of probe DNA would prevent biotin on the probe DNA being captured by the avidin on the electrode for the spatial effects. After the DFNP solution is incubated in a buffer solution containing target DNA, and then target DNA would combine probe DNA by forming double strand with complementary sequences, which caused hairpin open and eliminate steric hindrance to biotin. Afterwards, when avidin modified electrode was immersed in a solution after the hybridization event, the biotin of the DFNP could have attached to avidin on the electrode and thus was captured on the electrode. The electrochemical signals of MB of signal DNA were measured by differential pulse voltammetry (DPV). Taking advantage of amplification effects of the Au nanoparticle (AuNP) and binding specificity of the hairpin probe, this biosensor greatly simplifies the electrochemical detection method of DNA and displays high specificity.