Fourth Time's the Charm

This week my team and I were supposed to get in the field to collect one final set of samples for the first chapter of my research. However, thanks to some health circumstances, we had to postpone our trip, which meant that I went to the lab to work on sample preparations for more laser work. Why is this week's blog titled the way it is? Well there is no handbook for how to do a lot of the techniques I am using in my research because microplastics as a research field is still quite young. It has taken four tries to find a way to both safely transport microplastic samples to the laser lab from the marine lab (more than an hour drive) and to analyze them at the lab. Here are all the different ways that I have tried to go through this process and at the end I will show you pictures of the final method that I have decided on.

Attempt 1: leave microplastics on top of the filter paper in petri dishes. When I clean the microplastics of any adhesive materials (chemicals or biological residue), I rinse the samples with a chemical detergent and filter the liquids over filter paper. I then remove the filter paper and place it in a petri dish for counting and analysis. I originally envisioned that this method would work flawlessly for laser analysis, but I found out pretty quickly that I had some challenges to solve. For one, the stage (the part of the microscope that you put samples on) is motorized and controlled by a joystick. The stage moves with a minimum step size of 50 nanometers, and therefore it took a long time to search through a 7 cm diameter filter paper. The other challenge was that the objective lenses on the microscope (these are the lenses that you switch to increase magnification levels) were angled in such a way that they would come in contact with the edge of the petri dish because the petri dish was too tall.

Attempt 2: leave microplastics on top of the filter paper in petri dishes but plate the filter paper inside the lid--which is much shorter than the base--and use marker to outline the location of the microplastics. I thought this idea was stellar but forgot that although it was unlikely that the particles would move on the filter paper, the filter paper would shuffle around in transit, and therefore drawing on the petri dish was not helpful. Again, I found that the petri dish lid was a little too tall to use under the Raman spectroscope. Back to the drawing board.

Attempt 3: hold the microplastics in flat well plates. You have seen many pictures of flat well plates here on the blog because I have used them for a while to try and fix the problem. They do not interfere with the spectroscope's objective lenses, but they have really large wells and the cover slips provided don't fit snugly, so microplastics can move from one well to another. I used to spend 30 minutes+ at the laser lab sorting out microplastics and placing them back in their original locations.

Attempt 4: placing microplastics in concave microscope slides. While most microscope slides are flat pieces of glass, some slides have one, two, or three concave sections to hold very small items for observation. You can see the concavity clearly in the picture on the right. The concave areas are still quite large, but I have a magnifying glass that I bring to the lab to make finding the particles easier. I also group all the particles close together so that when I find one microplastic I don't have to move far to find the rest in a single sample. I also bring a small light that helps me find the microplastics, since many are colored and a bit reflective. The downside to this method is that I need to have a highly organized system for which sample is which, and I need to bring a small box of extra tools with me to the lab when I go. This system also requires a bit more preparation time, but this week I made more than 50 slides ready for analysis. Next week looks like more laser analysis, and I am excited to see how many more of the particles I have removed are actually microplastics. 

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