Detection and identification of microplastic particles in complex environmental samples or tissues is challenging due to the similarity in size and chemistry of natural and plastic materials in these samples. Measurement by flow cytometry and data analysis by a viSNE-based protocol developed at Eawag1,2 has proven useful to detect microplastic particles in stream biofilms, stream water, tissue and feces. viSNE. Originally developed for leukemia research, it is a tool to map high-dimensional cytometry data onto 2D while conserving high-dimensional structure and is based on the t-Distributed Stochastic Neighbor Embedding (t-SNE) algorithm3. Data is interpreted and particle types are quantified by comparison to reference data sets. Metrics for comparison include light scattering and fluorescence, which, when combined together, may provide a “fingerprint” of microplastics in complex samples. The detection limits of this approach in terms of both particle size and resolution of polymer identity are still unknown. By developing a database using a suite of known microplastic particles with various polymers, both in simple and complex media, this would provide a platform on which to analyse natural samples where unknown microplastics are present.
Within the framework of a Master’s thesis, the proposed project aims to establish a database of optical properties of microplastic particles based on flow cytometry data. Data analysis will be done by the viSNE-based protocol to characterize the detection limits in environmental samples with a focus on stream biofilms. To test the viSNE system, a relevant environmental exposure scenario will be constructed to assess microplastic particles in complex media. Stream biofilms are a potential sink for microplastic particles that sediment and interact with the extracellular polymeric substances excreted by biofilm-associated microorganisms, and thus make for an ideal proof of concept framework. Field sampling and controlled growth (setup available at Eawag) of biofilms will be realized in collaboration with Dr Ahmed Tlili/Eawag Environmental Toxicology Department. Guidance in analysis of samples by flow cytometry and data evaluation will be provided by Alexandra Kroll (Ecotox Centre). Microplastic particles from different origin (primary and secondary microplastic particles) will be selected to cover relevant sizes, aspects (e.g. spheres, fibres), polymer types, and additives in collaboration with Dr Denise Mitrano/ Eawag Process Engineering Department.
Suitable candidates for this project are expected to hold a BSc degree in biology, environmental sciences or a related discipline. For further information, please contact Alexandra Kroll, Ahmed Tlili or Denise Mitrano.
1 Sgier L, Freiman R, Zupanic A, Kroll A. (2016) Flow cytometry combined with viSNE for the analysis of microbial biofilms and detection of microplastics. Nat Comm 7(11587).
2 Sgier, L., Merbt, S. N., Tlili, A., Kroll, A., Zupanic, A. (2018) Characterization of Aquatic Biofilms with Flow Cytometry. J Vis Exp (136), e57655, doi:10.3791/57655.
3 Amir el-AD, Davis KL, Tadmor MD, Simonds EF, Levine JH, Bendall SC, Shenfeld DK, Krishnaswamy S, Nolan GP, Pe'er D. (2013) viSNE enables visualization of high dimensional single-cell data and reveals phenotypic heterogeneity of leukemia. Nat Biotechnol. 31(6):545-52.