Amino-modified MNPs were synthesized by coprecipitation
iron salts, according to a previously reported procedure [26]. In
order to covalent immobilization of aptamer on the surface of
amino-modified MNPs, APTES-modified MNPs were activated with
glutaraldehyde. Then these groups can react with amino-modified
aptamers. Therefore, 1.5300 g of APTES-modified MNPs was added
to 5% glutaraldehyde aqueous solution and stirred overnight at
room temperature. The materials were subsequently washed three
times with deionized water to remove excess glutaraldehyde