Iron oxide nanoparticles were synthesized through the co-precipitation method as described by Mérida et al23 (link) Briefly, deionized water was degassed with nitrogen for 30 minutes and an aqueous solution of iron (II) and iron (III) salts was prepared using a molar ratio Fe3+:Fe2+ of 2:1. The iron solution was sonicated and degassed, and the reaction was heated to 85°C, followed by the addition of ammonium hydroxide (Thermo Fisher Scientific, Waltham, MA, USA). The reaction was kept at 85°C for 1 hour, and the pH was maintained between 8 and 9 by adding small aliquots of NH4OH as needed. The resultant iron oxide solution was cooled at room temperature (RT) and peptized using tetramethylammonium hydroxide (Alfa Aesar, Tewksbury, MA, USA).
To coat the particle with poly(ethylene) glycol (PEG), oleic acid (OA, 90%, Sigma-Aldrich, St. Louis, MO, USA) was adsorbed onto the particles by adding 15 g OA/g SPIONs, followed by ultrasonication (Q700, Qsonica Sonicators, Newtown, CT, USA) for 15 minutes. The mixture was heated to 50°C and allowed to react for 2 hours. SPIONs were precipitated using twice the volume of ethanol (200 proof, Decon Labs, King of Prussia, PA, USA) and magnetically decanted to recover the particles, followed by suspension in toluene (>98%, Sigma-Aldrich).
To coat the particle with poly(ethylene) glycol (PEG), oleic acid (OA, 90%, Sigma-Aldrich, St. Louis, MO, USA) was adsorbed onto the particles by adding 15 g OA/g SPIONs, followed by ultrasonication (Q700, Qsonica Sonicators, Newtown, CT, USA) for 15 minutes. The mixture was heated to 50°C and allowed to react for 2 hours. SPIONs were precipitated using twice the volume of ethanol (200 proof, Decon Labs, King of Prussia, PA, USA) and magnetically decanted to recover the particles, followed by suspension in toluene (>98%, Sigma-Aldrich).
