{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T17:55:37Z","timestamp":1785866137017,"version":"3.56.0"},"posted":{"date-parts":[[2026,2,23]]},"group-title":"Bioengineering","reference-count":32,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,2,23]],"date-time":"2026-02-23T00:00:00Z","timestamp":1771804800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"name":"National Institutes of Health (NIH), US","award":["P41EB032840"],"award-info":[{"award-number":["P41EB032840"]}]},{"name":"National Institutes of Health (NIH), US","award":["R01CA187427"],"award-info":[{"award-number":["R01CA187427"]}]},{"name":"National Institutes of Health (NIH), US","award":["R01HL157712"],"award-info":[{"award-number":["R01HL157712"]}]},{"name":"National Institutes of Health (NIH), US","award":["R01CA250512"],"award-info":[{"award-number":["R01CA250512"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,2,23]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:sec>\n                  <jats:title>Significance<\/jats:title>\n                  <jats:p>Collagen autofluorescence provides valuable intrinsic contrast for assessing tissue structure, composition, and pathology. However, a comprehensive understanding of the fluorescence properties across different collagen types remains limited. This knowledge gap may limit the development of advanced label-free fluorescence spectroscopy and imaging techniques for specific tissue characterization and diagnostic applications.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Aim<\/jats:title>\n                  <jats:p>This study aims to comprehensively characterize the fluorescence intensity excitation-emission matrices (I-EEMs) and time-resolved excitation-emission matrices (TR-EEMs) of collagen standards from Types I, II, III, IV, and V obtained from various organ sources under both dry and hydrated conditions, to identify optimal excitation-emission parameters for each collagen type discrimination, and to establish a reference dataset that supports future research in label-free tissue characterization.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Approach<\/jats:title>\n                  <jats:p>We employed a time-resolved fluorescence spectroscopy system equipped with an optical parametric oscillator laser (excitation: 200-2000 nm, pulse width: 30 ps) as an excitation source to generate I-EEMs and TR-EEMs of human and bovine collagen Types I-V. The fluorescence light was obtained by a multichannel plate photomultiplier tube through a monochromator (spectral range: 200-1000 nm). Measurements were conducted using collagen standards, under both dry and hydrated states. Additionally, photobleaching effects were assessed to ensure the reliability and reproducibility of fluorescence data.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Each collagen type exhibited distinct I-EEM and TR-EEM signatures, with fluorescence lifetimes ranging from 2.5 ns (Type III, bovine skin) to 5.3 ns (Types II and V). Fibrillar collagens (Types I and V) displayed broader I-EEMs, whereas basement membrane collagen (Type IV) showed the narrowest spectral distribution. Organ-source-dependent variations were evident within the same collagen type. Type I collagen from human placenta exhibited an inverse lifetime\u2013emission wavelength relationship compared to bovine sources. Hydration consistently red-shifted emission peaks into the 395\u2013420 nm range and reduced fluorescence lifetimes across all collagen types (e.g., Type I bovine Achilles tendon: 3.2\u20135.0 ns dry vs. 3.0\u20134.5 ns hydrated). Despite excitation wavelength- and fluence-dependent photobleaching of fluorescence intensity, fluorescence lifetimes remained relatively stable, confirming the robustness of lifetime-based measurements.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>This study establishes a comprehensive reference dataset for the fluorescence properties of collagen Types I-V and demonstrates the potential of combined I-EEMs and TR-EEMs analysis for tissue characterization. The results highlight species-, organ-, type-, and environment-specific optical fingerprints of similar collagens, which must be considered before implementing more in-depth studies on how the optical properties of collagen change in different medical applications.<\/jats:p>\n                <\/jats:sec>","DOI":"10.64898\/2026.02.21.706506","type":"posted-content","created":{"date-parts":[[2026,2,23]],"date-time":"2026-02-23T22:50:11Z","timestamp":1771887011000},"source":"Crossref","is-referenced-by-count":1,"title":["Fluorescence Properties of Collagen Types I-V: A Comprehensive Study of Spectral and Lifetime Characteristics"],"prefix":"10.64898","author":[{"given":"Xuhui","family":"Liu","sequence":"first","affiliation":[{"name":"Department of Biomedical Engineering, University of California, Davis, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexandra C.","family":"Adams","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, University of California, Davis, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiangnan","family":"Zhou","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, University of California, Davis, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Julien","family":"Bec","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, University of California, Davis, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laura","family":"Marcu","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, University of California, Davis, United States"},{"name":"Department of Neurological Surgery, University of California, Davis, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026022605001429000_2026.02.21.706506v1.1","doi-asserted-by":"publisher","DOI":"10.1146\/annurev.biochem.77.032207.120833"},{"key":"2026022605001429000_2026.02.21.706506v1.2","doi-asserted-by":"publisher","DOI":"10.1038\/s41578-020-0213-1"},{"key":"2026022605001429000_2026.02.21.706506v1.3","doi-asserted-by":"publisher","DOI":"10.1101\/cshperspect.a004978"},{"key":"2026022605001429000_2026.02.21.706506v1.4","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.94.5.1852"},{"key":"2026022605001429000_2026.02.21.706506v1.5","doi-asserted-by":"publisher","DOI":"10.4103\/1947-2714.92892"},{"key":"2026022605001429000_2026.02.21.706506v1.6","doi-asserted-by":"publisher","DOI":"10.1002\/ar.23330"},{"key":"2026022605001429000_2026.02.21.706506v1.7","doi-asserted-by":"publisher","DOI":"10.3390\/ijms24087631"},{"key":"2026022605001429000_2026.02.21.706506v1.8","doi-asserted-by":"publisher","DOI":"10.1038\/s41598-024-61178-0"},{"key":"2026022605001429000_2026.02.21.706506v1.9","doi-asserted-by":"crossref","unstructured":"L. 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