After centrifugation, the total volume of low-density material above the density gradient medium cushion (~1250 μL) was collected via micropipette (Figure , step 3). The micropipette tip was held at the interface of the low-density water and density gradient medium during pipetting since the majority of our organic INSs should have collected at this interface. The density gradient medium cushion was then removed and discarded, except for approximately 50-100 μL of density gradient medium at the bottom of the centrifuge tube, which should contain any high-density material in the form of a pellet (Figure , step 3). This remaining 50-100 μL density gradient medium and any high-density material was resuspended in 50 μL of ultrapure water, transferred to a clean vessel, and then 1200 μL of ultrapure water were added to bring the total volume to between 1300 and 1350 μL (Figure , step 4).