Bovine serum albumin, 3-(4,5-dimethyl-2-thiazyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT), dimethyl sulfoxide, phosphate-buffered saline (pH 7.4), N-dicyclohex-ylcarbodiimide, dicyclohexylurea, N-hydroxysuccinimide (NHS), and doxorubicin hydrochloride were purchased from Sigma-Aldrich (St Louis, MO, USA). Ammonium ferric sulfate dodecahydrate, hydroxylamine hydrochloride, 1,10-phenanthroline, and sodium acetate were purchased from JiangLai Biological (Shanghai, People’s Republic of China). All solvents were of high-performance liquid chromatography grade. An Annexin V-fluorescein isothiocyanate (FITC) apoptosis detection kit was supplied by Beyotime Institute of Biotechnology (Shanghai, People’s Republic of China). Fe3O4 was prepared as described by Li et al.22 (link) All reagents were of analytical grade.