Preparation of a contrast media dilution series in Ficoll solution
Preparing contrast media dilution series in Ficoll instead of water helps prevent sedimentation during MRI experiments. Compared to agarose, Ficoll offers the additional advantage of being free of air bubbles, which can interfere with imaging. Ficoll exhibits a mild intrinsic T1 signal—i.e., solutions appear slightly brighter than those prepared in water or PBS. This property is particularly relevant for dilution series involving Gd-based contrast agents but generally does not significantly influence T2 or T2* measurements of iron oxide nanoparticles.
Preparation of 100 mL Ficoll Solution at a Density of 1.07 g/mL
To prepare a 100 mL Ficoll solution with a final density of 1.07 g/mL (as calculated from the Ficoll PM 400 instruction sheet):
- Weigh 7 g of Ficoll powder.
- Add 3 g of distilled water (calculated as: 100 mL × 1.07 g/mL − 18.7 g = 88.3 g).
- Heat the mixture to 50–60 °C while stirring on a hot plate. Monitor the temperature using a thermometer.
- Dissolve the powder gradually over 20–30 minutes, until a homogenous, viscous solution is formed. It is recommended to cover the container during heating to minimize water evaporation.
- Ensure that the powder is completely dissolved and that there is no loss of water or sample, as this would alter the final concentration.
- Filter the solution first through a 45 μm membrane filter (e.g., using an HPLC solvent filtration setup), then further filter through a 0.2 μm syringe filter into sterile vials.
Although the procedure is straightforward, it requires moderate heating and some patience during the dissolution phase. Note that Ficoll is a stable polymer in aqueous solution but is not stable in strong acidic conditions.