Colloidal Iron Dextran (FeDex)

• 1. Mix 5 mL of 1.2 m FeCl₂ and 5 mL of 1.8 m FeCl₃ in a 250-mL glass beaker. Add 5 mL of 30% NH₄OH dropwise and stir gently using a magnetic stirrer and flea.

  • A dark brown/black precipitate/sludge will form.

• 2. Place the beaker on top of a strong magnet for 1 min to allow the precipitate to migrate toward the magnet. Discard the top liquid layer.

  • A high-energy neodyminium magnet is required for this step. The magnet from a Dynal MPC-L Magnetic Particle Concentrator (Invitrogen/Life Technologies) is suitable.

• 3. Remove the magnet, and wash the precipitate by resuspending it with gentle swirling in 50–100 mL at a time of 5% NH₄OH. Place the resuspension back in the magnetic field and discard the liquid. Repeat twice with ddH₂O.

  • The precipitate must be thoroughly resuspended to ensure it is washed properly.

• 4. Remove the magnet, resuspend the precipitate in 40 mL of 0.3 m HCl, and stir for 30 min.

• 5. Add 2 g of dextran (M_r of 40,000) and stir for 40 min.

• 6. Dialyze extensively in ddH₂O for 2 d at 4°C, using dialysis tubing with a molecular weight cut-off (MWCO) of 10,000.

• 7. Centrifuge in a Sorvall SS-34 rotor or equivalent for 15 min at 26,900g to remove large aggregates.

• 8. Filter through a 0.22-µm filter, and store at 4°C for up to 2 mo.

  • The FeDex solution will be black/very dark brown. This recipe was adapted from Rodriguez-Paris et al. (1993).

• © 2016 Cold Spring Harbor Laboratory Press