Imaging the Uptake and Effects of Microplastics on Organisms by Coherent Raman Scattering Microscopy

In order to determine the effects that the uptake of microplastics has on various organisms, novel means of detecting and imaging microplastics inside cells and organisms are needed. In the best case, such methods should provide entirely label-free contrast, while still being chemically specific. In optical microscopy, this is best realized by utilizing Raman scattering, which is the inelastic scattering of light at molecular bonds. While spontaneous Raman scattering is too slow for most imaging applications, coherent Raman scattering (CRS) can be employed at imaging speeds up to video-rate. We have developed and employed a fully customizable CRS microscope, which allows us to visualize the structure of organic and biological samples in the same imaging process as the identification and imaging of microplastics in these samples. This system allows us to analyze a wide range of effects of the uptake of microplastics, e.g. by plant seedling up to monitoring fitness parameters, such as lipid concentration in C. elegans nematodes. A variety of techniques are combined in one setup. These techniques include coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) using optical parametric oscillators to probe different Raman resonances, as well as second harmonic generation (SHG) to probe tissue structure. This gives us the opportunity to use a wide range of analysis techniques to collect information with biological and medical relevance. These methods include volumetric imaging and hyperspectral analysis to produce quantitative data about the composition of the examined samples. In this contribution we will provide detailed information about the setup and recent improvements, and demonstrate its wide range of applications with particular emphasis on analyzing the effects of microplastics uptake by organisms