Firstly, a sum of 30 mL of primer DNA (1 mM), 2 mL of of sodium phosphate buffer (1 M, pH 5.5) and 2 mL of TCEP solution (30 mM) were mixed, which was then incubated for 1 h at room tempera- ture. The mixture was purified by Amicon-10 K for 10 times using buffer A (0.1 M NaCl, 0.05% Tween-20, 0.1 M sodium phosphate buffer, pH 7.3). Then, in order to conduct invertase conjugation, 1 mg of sulfo-SMCC was added into 400 mL of invertase solution (dissolved in buffer A), which was incubated for 1 h on a roller. The obtained mixture was purified through centrifugation and Ami- con-100 K using Buffer A by 10 times. Finally, the obtained sulfo- SMCC-activated invertase was mixed with the primer DNA, which was incubated for 48 h at room temperature. The mixture was purified by Amicon-100 K for 10 times using Buffer A.