Evaluation of filter substrates for concurrent optical photothermal infrared and Raman spectroscopy in microplastic analysis
- 1Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745 Jena, Germany
- 2Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany
- 3Department for Medical Engineering and Biotechnology, University of Applied Sciences Jena, Carl-Zeiss-Promenade 2, 07745 Jena, Germany
Abstract
Optical photothermal infrared (O-PTIR) spectroscopy is an emerging technique to analyze submicron mid-infrared absorption. It can be combined with concurrent, co-located Raman spectroscopy on the same instrument platform, offering considerable potential for microplastic analysis. However, since measurements are typically performed directly on collection filters, substrate selection becomes a critical yet un-examined factor for these concurrent modalities. Here, we characterized nine commercially available filter substrates, namely Anodisc, silicon, gold-coated PET, gold-coated PC, silver, glass and quartz microfiber, PC, and cellulose, for O-PTIR and Raman analysis using 14 µm and 7 µm PMMA microplastic beads. Spectral fidelity was quantified via hit quality indices against a CaF2 reference. Our results show that substrate suitability is governed by modality-specific requirements. O-PTIR demands mid-infrared spectral neutrality and is additionally sensitive to the substrate surface, whereas the quality of Raman spectra primarily depends on the absence of substrate Raman bands. Beyond spectral match quality, the reproducibility of PMMA spectra is consistently higher in the Raman channel than in the O-PTIR channel. This difference is attributed to O-PTIR’s sensitivity to local thermal contact and surface morphology, which introduce measurement variability absent in direct Raman scattering. Of the tested substrates, Anodisc and gold-coated PET performed the best in both modalities and with both particle sizes. These findings demonstrate that recommendations for substrates established for conventional FTIR or Raman microscopy cannot be transferred directly to O-PTIR. They also provide an evidence-based framework for selecting substrates in multimodal microplastic analysis workflows.
Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s00216-026-06735-4.
Related
- Label-free identification and classification of leukocyte subpopulations in peripheral blood smears by optical photothermal infrared spectroscopy
- Monitoring Early Infection Dynamics in Live Spodoptera frugiperda (Sf) 9 Cells via Optical Photothermal Infrared (OPTIR) Spectroscopy.
- Machine-learning-enhanced Optical Photothermal infrared (O-PTIR) spectroscopy for rapid simultaneous identification of multiple metabolites to monitor biotransformations: proof of concept on Brewer's spent grain (BSG)
- TCA precipitation and ethanol/HCl single-step purification evaluation: One-dimensional gel electrophoresis, bradford assays, spectrofluorometry and Raman spectroscopy data on HSA, Rnase, lysozyme - Mascots and Skyline data
- A unified framework for sensitivity comparison across stimulated Raman, stimulated Raman photothermal, and mid-infrared photothermal microscopy
BibTeX
@article{shiwani2026evaluation,
title = {{Evaluation of filter substrates for concurrent optical photothermal infrared and Raman spectroscopy in microplastic analysis}},
author = {Shiwani Shiwani and Shravan Raghunathan and Jürgen Popp and Iwan W. Schie and Christoph Krafft},
journal = {Analytical and Bioanalytical Chemistry},
year = {2026},
month = aug,
doi = {10.1007/s00216-026-06735-4},
url = {https://doi.org/10.1007/s00216-026-06735-4},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Evaluation of filter substrates for concurrent optical photothermal infrared and Raman spectroscopy in microplastic analysis
AU - Shiwani Shiwani
AU - Shravan Raghunathan
AU - Jürgen Popp
AU - Iwan W. Schie
AU - Christoph Krafft
PY - 2026
DA - 2026/08/25
JO - Analytical and Bioanalytical Chemistry
DO - 10.1007/s00216-026-06735-4
UR - https://doi.org/10.1007/s00216-026-06735-4
AB - Optical photothermal infrared (O-PTIR) spectroscopy is an emerging technique to analyze submicron mid-infrared absorption. It can be combined with concurrent, co-located Raman spectroscopy on the same instrument platform, offering considerable potential for microplastic analysis. However, since measurements are typically performed directly on collection filters, substrate selection becomes a critical yet un-examined factor for these concurrent modalities. Here, we characterized nine commercially available filter substrates, namely Anodisc, silicon, gold-coated PET, gold-coated PC, silver, glass and quartz microfiber, PC, and cellulose, for O-PTIR and Raman analysis using 14 µm and 7 µm PMMA microplastic beads. Spectral fidelity was quantified via hit quality indices against a CaF2 reference. Our results show that substrate suitability is governed by modality-specific requirements. O-PTIR demands mid-infrared spectral neutrality and is additionally sensitive to the substrate surface, whereas the quality of Raman spectra primarily depends on the absence of substrate Raman bands. Beyond spectral match quality, the reproducibility of PMMA spectra is consistently higher in the Raman channel than in the O-PTIR channel. This difference is attributed to O-PTIR’s sensitivity to local thermal contact and surface morphology, which introduce measurement variability absent in direct Raman scattering. Of the tested substrates, Anodisc and gold-coated PET performed the best in both modalities and with both particle sizes. These findings demonstrate that recommendations for substrates established for conventional FTIR or Raman microscopy cannot be transferred directly to O-PTIR. They also provide an evidence-based framework for selecting substrates in multimodal microplastic analysis workflows. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s00216-026-06735-4.
SN - 1618-2642
SN - 1618-2650
ER -