Magnetic Fluid-Hydroxyl is the magnetic bead with hydroxyl groups –OH and the beads exhibits superparamagnetism. It consists of single-crystal Fe₃O₄ magnetic sphere core and being coated with dextran dispersed in phosphate buffered saline (PBS) solution. The structure of dextran provides a lot of hydroxyl groups –OH and this hydrophilic surface ensures the magnetic beads excellent dispersion ability and easy handling property in a wide variety of buffers. The beads can be directly used for biospecies separation, biomedical imaging and bioassay development.