February 27th - March 8th
Recently, I was responsible for running an iron particle sedimentation experiment to assess whether various iron particles developed for MRI and/or MPI iron cell tracking sediment when placed in cell culture media.
The iron particles we assessed were: MPIO (flash red and glacial blue), Molday-G, Synomag-D 50nm, Synomag-D 70 nm, Synomag-D PEG 50nm, Synomag-D PEG 70 nm, MPIO, PMAO, VivoTrax, and ProMag-1. Some of these particles had previously demonstrated aggregation when used to label cell cultures.
I ran three trials of the experiment. First, I ran one trial keeping all conditions as close to what they would normally be for a cell culture labelling experiment. The particles were loaded into 1 mL of cell culture media at a calculated volume, based on the typically used cell loading concentration. I waited 20 minutes after adding the particles to each Eppendorf tube and then analyzed the samples for any observable pellets. From this initial trial, we did not see any pellets after 20 minutes. However, after leaving these samples for 24 hours, pellets were clearly visible for MPIO, ProMag1, Molday-G and VivoTrax. However, it was extremely difficult to image these small pellets for use in a paper figure. The red colour of the cell culture media clashed with the reddish colour of the iron particles. Additionally, the small volumes of the pellets were just hard to see overall. This led to the development of the second trial of the experiment.
In trial 2, the volumes were increased 10-fold (both the volume of particle loaded and the volume of cell culture media). In this experiment, pellets were more clearly visible, and particles showed sedimentation after 20 minutes. There was an interesting result with the Synomag-D particles. The particle with a hydrodynamic diameter of 50 nm did not sediment, however the particle with a hydrodynamic diameter of 70 nm showed the most clearly visible pellet of all the samples. This could be a mechanism to explain the known poor performance of Synomag-D 70 nm with cell labelling.
There was a third trial to further enhance the image quality that could be captured of each iron particle pellet. Instead of media, I loaded 10 mL of PBS into 15 mL falcon tubes and added a uniform volume of 200 uL of each iron pellet to each labelled tube. This trial revealed the same results as trial 2, with pellets that were more easily observed on a clear liquid backdrop.
Overall, I had the opportunity this week to explore more about the properties of the main iron particles used by our lab in MRI and/or MPI iron cell tracking experiments. I worked hands on with the particles which is useful training for future experiments where I will label cells with these iron particles. My personal reflection for this week is that I can do better to be more efficient when working in the lab. In the future, I will label necessary tubes and obtain equipment 20-30 minutes before starting the experiment to be as efficient as possible in the lab. Additionally, I have learned that optimization is an important process in running a new experiment. If I had not performed multiple trials of the sedimentation experiment and increased the volume to 10 mL, I would not have seen clear pellets from the iron particles. Lesson learned: optimization should not be rushed and should be well thought out! I'm looking forward to developing these deep critical thinking skills further in graduate school.