Optical photothermal infrared spectroscopy with simultaneously acquired Raman spectroscopy for two-dimensional microplastic identification

Abstract

In recent years, vibrational spectroscopic techniques based on Fourier transform infrared (FTIR) or Raman microspectroscopy have been suggested to fulfill the unmet need for microplastic particle detection and identification. Inter-system comparison of spectra from reference polymers enables assessing the reproducibility between instruments and advantages of emerging quantum cascade laser-based optical photothermal infrared (O-PTIR) spectroscopy. In our work, IR and Raman spectra of nine plastics, namely polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, silicone, polylactide acid and polymethylmethacrylate were simultaneously acquired using an O-PTIR microscope in non-contact, reflection mode. Comprehensive band assignments were presented. We determined the agreement of O-PTIR with standalone attenuated total reflection FTIR and Raman spectrometers based on the hit quality index (HQI) and introduced a two-dimensional identification (2D-HQI) approach using both Raman- and IR-HQIs. Finally, microplastic particles were prepared as test samples from known materials by wet grinding, O-PTIR data were collected and subjected to the 2D-HQI identification approach. We concluded that this framework offers improved material identification of microplastic particles in environmental, nutritious and biological matrices.

Raman Spectroscopic Imaging of Human Bladder Resectates towards Intraoperative Cancer Assessment

“…The loadings of three endmembers were coded with red, green and blue colors to display the distribution of the three selected components. In sample 3T, one pixel at the lower margin next to OCT is assigned to the well-known Raman signature of polystyrene (PS) [ 18 ]. The Raman intensities of PS bands are almost 1000 times more intense than the Raman bands of tissue-related materials.…”

“…The band positions of the measured spectrum and the library spectrum agreed very well. Deviations occurred for relative band intensities that might be corrected by an intensity calibration procedure, which has recently been described [ 18 ]. Although the unknown spectrum in sample 2N gives a reasonable HQI = 68.7 with library entry cellulose acetate sorbate ( Supplementary Figure S9 ), numerous bands deviate, making the assignment less reliable.…”

Optical photothermal infrared spectroscopy and discrete wavenumber imaging for high content screening of single cells

“…Details were previously described. 22 The IR laser repetition rate was set at 100 kHz at 980 ns per pulse. The O-PTIR single spectra and single wavenumber images were acquired at 47% IR power, 37% probe power, 1000 cm −1 s −1 scan speed, and a 2× detector gain using a 40× Cassegrain objective lens and a collection optic in transmission mode.…”

Hyperspectral and Nanosecond Temporal Resolution Widefield Infrared Photothermal Heterodyne Imaging

“…Vibrational optical spectroscopies stand as important, label-free imaging modalities for the complete structural and functional characterization of chemical, environmental and biological specimens. − Two major embodiments involve Raman scattering and infrared (IR) absorption spectroscopy. Raman microscopy possesses a relatively high spatial resolution of ∼300 nm.…”