Firstly, 5 mL of Streptavidin-MNBs was washed three times by using buffer A to remove the surfactants. Then, 50 mL of buffer A was added into the Streptavidin-MNBs suspension. One microliters above Streptavidin-MNBs suspension was added into a tube and 10 mL of capture DNA (10 mM in TE buffer) was added to bind on the Streptavidin-MNBs, which was placed on a roller for 30 min. It was washed using buffer A for 5 times and the Streptavidin-MNBs were separated by a magnet. Then, the primer DNA with DNA– invertase conjugation and different target DNA were mixed with the Streptavidin-MNBs. All samples were performed in 80ml solution containing 50 mM Tris–HCl (pH 8.0) and 5 mM MgCl2 and incubated at 37 °C. Finally, 15 U of polymerase Klenow frag- ment exo was added and allowed to react in 37 °C for 1 h.