Detection of microplastics via a frequency-shifted excitation confocal micro-differential, spatial heterodyne, Raman spectrometer with echelle-mirror structure

We report on the detection of microplastics using a system that integrates frequency-shifted excitation differential spectroscopy, confocal microscopy, and spatial heterodyne Raman spectroscopy with an echelle-mirror structure. By optimizing the optical path design with an echelle grating and mirror configuration, the system simultaneously exhibits high optical throughput and a spectral resolution of 1.59 cm^-1 with a single-order coverage of 1341 cm^-1. The frequency-shifted differential technique eliminates interference from background fluorescence. The signal-to-noise ratios of differentially reconstructed spectra were improved by at least two-fold relative to the original spectra. The detection of various microplastics, including those in mixed samples and those embedded in edible sea salt, was demonstrated in the Raman spectra. These results indicate strong potential applications involving fluorescent interference, such as microplastic analysis.