Differentiation of Microplastic Particles From Phytoplankton Cells Using FlowCam Fluorescent Trigger Mode ​

Microplastics are of increasing concern globally, however it is difficult to quantify and image environmental samples in a cost-effective manner that minimizes contamination. FlowCam is an ideal instrument for this work as it not only quantifies and sizes particles, but also photographs each particle, which can then be compared to a library catalog for further categorization. The objective of this work was to develop a FlowCam methodology to distinguish between naturally-fluorescent phytoplankton and fluorescently-stained plastic particles as an application for analysis of environmental samples. To develop this methodology, we initially used monocultures of two phytoplankton, a flagellate (Tetraselmis chuii) and a diatom (Chaetoceras neogracile) to identify the fluorescent signatures of the phytoplankton. These were compared to the signature from virgin LDPE microplastic beads, as well as these same beads which were stained with Nile Red - which adheres to the plastic and florescences. FlowCam exposes the cells/particles to a 488 nm laser and detects two different wavelengths of fluorescence (Channel 1 - 650 nm and Channel 2 - 525 nm). In a roughly 50:50 mix of Nile Red-stained LDPE beads and each phytoplankton monoculture, this methodology successfully differentiated between algal cells and plastic particles. Next steps are to explore if this methodology continues to differentiate between plastic and phytoplankton cells when phytoplankton cells are more abundant than plastic, which better represents environmental conditions, and to process environmental samples.

For more information: mithornton@eckerd.edu