The supernatantwas poured out, and 1 ml of 70% ethanol was added.Centrifugation at 13,000 rpm for 10 min was carriedout. The supernatant was poured out, and the pelletwas dried in a 65°C incubator for 30 min. The drypellet was suspended in 20 μl ddH2O, and the DNAsuspension was stored at −20°C until used. The DNAwas qualified and quantified using BioDrop DuO(BioDrop, England).