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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\u00a0\u00b5m and 7\u00a0\u00b5m PMMA microplastic beads. Spectral fidelity was quantified via hit quality indices against a CaF\n                    <jats:sub>2<\/jats:sub>\n                    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\u2019s 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.\n                  <\/jats:p>","DOI":"10.1007\/s00216-026-06735-4","type":"journal-article","created":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T15:17:29Z","timestamp":1787671049000},"page":"7409-7420","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Evaluation of filter substrates for concurrent optical photothermal infrared and Raman spectroscopy in microplastic analysis"],"prefix":"10.1007","volume":"418","author":[{"given":"Shiwani","family":"Shiwani","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shravan","family":"Raghunathan","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"J\u00fcrgen","family":"Popp","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Iwan W.","family":"Schie","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Christoph","family":"Krafft","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,8,25]]},"reference":[{"key":"6735_CR1","doi-asserted-by":"publisher","unstructured":"Geyer R, Jambeck JR, Law KL. Production, use, and fate of all plastics ever made. Sci Adv. 2017;3:e1700782.\u00a0https:\/\/doi.org\/10.1126\/sciadv.1700782","DOI":"10.1126\/sciadv.1700782"},{"key":"6735_CR2","doi-asserted-by":"publisher","first-page":"218","DOI":"10.1177\/0036850419867204","volume":"102","author":"CJ Rhodes","year":"2019","unstructured":"Rhodes CJ. Solving the plastic problem: from cradle to grave, to reincarnation. Sci Prog. 2019;102:218\u201348. https:\/\/doi.org\/10.1177\/0036850419867204.","journal-title":"Sci Prog"},{"key":"6735_CR3","doi-asserted-by":"publisher","first-page":"11692","DOI":"10.1021\/acs.est.0c03057","volume":"54","author":"VN de Ruijter","year":"2020","unstructured":"de Ruijter VN, Redondo-Hasselerharm PE, Gouin T, Koelmans AA. Quality criteria for microplastic effect studies in the context of risk assessment: a critical review. Environ Sci Technol. 2020;54:11692\u2013705. https:\/\/doi.org\/10.1021\/acs.est.0c03057.","journal-title":"Environ Sci Technol"},{"key":"6735_CR4","doi-asserted-by":"publisher","first-page":"900","DOI":"10.1056\/NEJMoa2309822","volume":"390","author":"R Marfella","year":"2024","unstructured":"Marfella R, Prattichizzo F, Sardu C, Fulgenzi G, Graciotti L, Spadoni T, et al. Microplastics and nanoplastics in atheromas and cardiovascular events. N Engl J Med. 2024;390:900\u201310. https:\/\/doi.org\/10.1056\/NEJMoa2309822.","journal-title":"N Engl J Med"},{"key":"6735_CR5","doi-asserted-by":"publisher","first-page":"672","DOI":"10.1126\/science.abe5041","volume":"371","author":"AD Vethaak","year":"2021","unstructured":"Vethaak AD, Legler J. Microplastics and human health. Science. 2021;371:672\u20134. https:\/\/doi.org\/10.1126\/science.abe5041.","journal-title":"Science"},{"key":"6735_CR6","doi-asserted-by":"publisher","first-page":"781","DOI":"10.1016\/j.chemosphere.2017.05.096","volume":"182","author":"L Hermabessiere","year":"2017","unstructured":"Hermabessiere L, Dehaut A, Paul-Pont I, Lacroix C, Jezequel R, Soudant P, et al. Occurrence and effects of plastic additives on marine environments and organisms: a review. Chemosphere. 2017;182:781\u201393. https:\/\/doi.org\/10.1016\/j.chemosphere.2017.05.096.","journal-title":"Chemosphere"},{"key":"6735_CR7","doi-asserted-by":"publisher","first-page":"7068","DOI":"10.1021\/acs.est.9b01517","volume":"53","author":"KD Cox","year":"2019","unstructured":"Cox KD, Covernton GA, Davies HL, Dower JF, Juanes F, Dudas SE. Human consumption of microplastics. Environ Sci Technol. 2019;53:7068\u201374. https:\/\/doi.org\/10.1021\/acs.est.9b01517.","journal-title":"Environ Sci Technol"},{"key":"6735_CR8","doi-asserted-by":"publisher","DOI":"10.1016\/j.envint.2020.106274","volume":"146","author":"A Ragusa","year":"2021","unstructured":"Ragusa A, Svelato A, Santacroce C, Catalano P, Notarstefano V, Carnevali O, et al. Plasticenta: first evidence of microplastics in human placenta. Environ Int. 2021;146:106274. https:\/\/doi.org\/10.1016\/j.envint.2020.106274.","journal-title":"Environ Int"},{"key":"6735_CR9","doi-asserted-by":"publisher","DOI":"10.1016\/j.mex.2023.102143","volume":"10","author":"LHMLM Santos","year":"2023","unstructured":"Santos LHMLM, Insa S, Arx\u00e9 M, Buttiglieri G, Rodr\u00edguez-Mozaz S, Barcel\u00f3 D. Analysis of microplastics in the environment: identification and quantification of trace levels of common types of plastic polymers using pyrolysis-GC\/MS. MethodsX. 2023;10:102143. https:\/\/doi.org\/10.1016\/j.mex.2023.102143.","journal-title":"MethodsX"},{"key":"6735_CR10","doi-asserted-by":"publisher","first-page":"24458","DOI":"10.1021\/acs.analchem.5c04003","volume":"97","author":"B Ferreiro","year":"2025","unstructured":"Ferreiro B, Andrade JM, L\u00f3pez-Rosales A, Muniategui-Lorenzo S. Microplastic mass estimation using two-dimensional chemical images from quantum-cascade laser-based infrared spectrometers. Anal Chem. 2025;97:24458\u201367. https:\/\/doi.org\/10.1021\/acs.analchem.5c04003.","journal-title":"Anal Chem"},{"key":"6735_CR11","doi-asserted-by":"publisher","first-page":"13279","DOI":"10.1021\/acs.est.8b03438","volume":"52","author":"L Cabernard","year":"2018","unstructured":"Cabernard L, Roscher L, Lorenz C, Gerdts G, Primpke S. Comparison of Raman and Fourier transform infrared spectroscopy for the quantification of microplastics in the aquatic environment. 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TrAC Trends Anal Chem. 2018;109:214\u201326. https:\/\/doi.org\/10.1016\/j.trac.2018.10.010.","journal-title":"TrAC Trends Anal Chem"},{"key":"6735_CR14","doi-asserted-by":"publisher","DOI":"10.1021\/acs.analchem.6c02679","author":"S Shiwani","year":"2026","unstructured":"Shiwani S, Latka I, Islam SMM, Popp J, Schie IW. Characterizing the influence of filter substrates on Raman measurements of microplastics. Anal Chem. 2026. https:\/\/doi.org\/10.1021\/acs.analchem.6c02679.","journal-title":"Anal Chem"},{"key":"6735_CR15","doi-asserted-by":"publisher","first-page":"6791","DOI":"10.1007\/S00216-015-8850-8\/FIGURES\/11","volume":"407","author":"A K\u00e4ppler","year":"2015","unstructured":"K\u00e4ppler A, Windrich F, L\u00f6der MGJ, Malanin M, Fischer D, Labrenz M, et al. Identification of microplastics by FTIR and Raman microscopy: a novel silicon filter substrate opens the important spectral range below 1300 cm\u22121 for FTIR transmission measurements. 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Anal Bioanal Chem. 2021;413:5969\u201394. https:\/\/doi.org\/10.1007\/s00216-021-03498-y.","journal-title":"Anal Bioanal Chem"},{"key":"6735_CR21","unstructured":"Sigma Aldrich membrane filters for microplastics analysis. https:\/\/www.sigmaaldrich.com\/DE\/en\/technical-documents\/technical-article\/environmental-testing-and-industrial-hygiene\/drinking-water-testing\/membrane-filters-for-microplastics-analysis?srsltid=AfmBOooiBG_PiyQyKKq8xXUPZgYHGIKlqAGJSIeFZKiHHPkGdmZeYUT0. Accessed 26 Jun 2025"},{"key":"6735_CR22","doi-asserted-by":"publisher","first-page":"38642","DOI":"10.1021\/acsomega.6c01354","volume":"11","author":"A Thayyil-Raveendran","year":"2026","unstructured":"Thayyil-Raveendran A, Adak S, Shydliukh A, Redinger N, Hauptmann M, Schaible UE, et al. Free-electron laser-based extended wide-field mid-infrared photothermal imaging for biomedical and microplastic analysis. 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