The detection of deoxyribonucleic acid (DNA) has a very important significance in life sciences. The paper demonstrates a novel and effective electrochemical detection method of observing single nanoparticle (NP) collision events as signal label to amplify electrocatalytic activity for hydrazine electrooxidation in a sandwich-type DNA sensor. The Au NP was characterized by UV-vis spectrophotometer and transmission electron microscope (TEM). Hydrazine oxidation on DNA-modified Au NP was compared with that on Au NP by cycle voltammetry (CV). Via NaBH4 treatment the enhancement of electrocatalytic activity of DNA-modified Au NPs was proposed and applied to the sandwich-type DNA sensor. It is discussed by cyclic voltammetry, linear sweep voltammetry (LSV), and chronoamperometry (CA). The result showed that the Au NP of 3-4 nm diameters had large specific surface area and less prone to agglomeration with good electrocatalytic activity. Cyclic voltammetry displayed that the current of electrode increased 1.103-1.889 x 10(-8) A after NaBH4 treatment in the different concentrations of target DNA. Target DNA could be detected at concentration ranging from 1 pM to 100 nM and the detection limit was 1 pM. It can be applied to the development of even more sensitive biosensors. (C).2013 Elsevier Ltd. All rights reserved.