Rapid single-live-cell scanning via Fourier-transform infrared (FTIR) microscopy to elucidate microplastic-cell interactions

Measuring live cells by FTIR spectroscopy is challenging due to their small size and the absorbance of water in the mid-IR region. However, measuring cells in their live state is important to observe changes in the biological processes of cells that are unaffected by fixation and drying processes. Recently, ZnS hemispheres were used to sandwich live cells in a 6 µm layer of cell medium, which simultaneously limit the absorbance of water and increase the spatial resolution by x2.25, thereby enabling high quality spectra to be acquired from living cells. So far, this method has been used as an imaging technique to showcase the distribution of biomolecules within a single cell. In this work, we present an alternative use of these ZnS hemispheres as a high throughput screening tool. We obtained high quality spectra of a single cell at a measurement rate of ∼1 min/cell. We've applied this technique to observe the biochemical effects of various polystyrene microplastics on two mammalian cell lines (J774A.1 and A549), however the method can easily be expanded to other cell lines, microplastics, and alternative xenobiotics. Experiment design in short:•Cultivate cells and expose them to microplastics for 24 h•Seed a small volume of the suspension of the treated cells on the ZnS hemisphere•Obtain FTIR spectra of live-single-cells through the cell medium layer.