▎ 摘　　要

NOVELTY - Silica-based composite magnetic microspheres are obtained by coating a silica layer on a surface of graphene-coated nano-magnetic particle composite material. The silica layer has thickness of 180-200 nm. The graphene-coated variable phase nano-magnetic composite material has core-shell structure, shell comprising graphite shell containing multi-layered graphene shells with thickness of 5-50 nm and core as magnetic core. The phase of nano-magnetic particles comprise ( alpha )-iron-nitrogen compound and/or ( gamma )-iron-nitrogen compound. USE - Silica-based composite magnetic microspheres are used for extraction of DNA (claimed), and automation and development of high-throughput instrument. ADVANTAGE - The silica-based composite magnetic microspheres have high magnetic responsiveness, separating sensitiveness and same DNA separation characteristics. DETAILED DESCRIPTION - Silica-based composite magnetic microspheres are obtained by coating a silica layer on a surface of graphene-coated nano-magnetic particle composite material. The silica layer has thickness of 180-200 nm. The graphene-coated variable phase nano-magnetic composite material has core-shell structure, shell comprising graphite shell containing multi-layered graphene shells with thickness of 5-50 nm and core as magnetic core. The phase change of nano-magnetic particles has particle diameter of 10-90 nm. The phase of nano-magnetic particles comprise alpha -iron-nitrogen compound, gamma -iron-nitrogen compound, gamma -ferric nitride compound, gamma '-ferric nitride compound, epsilon -ferric nitride compound and/or alpha "-ferric nitride compound. INDEPENDENT CLAIMS are included for the following: (i) preparation of silica-based composite magnetic microspheres, which involves ultrasonically dispersing 20 mg graphene-coated nano-magnetic particle composite in 70 ml isopropanol containing 1% Tween 20 (RTM: polysorbate-type nonionic surfactant) for 10 minutes, dripping 10 ml isopropanol containing ethyl orthosilicate, adding predetermined amount of ammonia and deionized water, adjusting pH to 10, forming 100 ml suspension, centrifuging suspension at 45 degrees C for 1.5-2 hours, washing with anhydrous ethanol, resuspending pellets in absolute ethanol, removing impurities not covered on nano iron nitride composites by magnetic separation, low-speed centrifuging mixture, precipitating product out and drying product; (ii) usage of silica-based composite magnetic microspheres for DNA extraction; and (iii) extraction of DNA, which involves cleaving sample tissue or cells by predetermined method, to obtain lysate, removing other substances in lysate which may be adsorbed to silica-based composite magnetic microspheres, adding silica-based composite magnetic microspheres and coupling agent to lysate, combining silica-based composite magnetic microspheres with DNA, magnetically separating silica-based composite magnetic microspheres to which DNA is adsorbed and other materials in lysate and eluting DNA from silica-based composite magnetic microspheres. The coupling agent comprises mixed solution of salt and polyethylene glycol.