{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,14]],"date-time":"2026-05-14T16:15:44Z","timestamp":1778775344857,"version":"3.51.4"},"reference-count":43,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2021,5,20]],"date-time":"2021-05-20T00:00:00Z","timestamp":1621468800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["R21 EB019709"],"award-info":[{"award-number":["R21 EB019709"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["P30 GM131959"],"award-info":[{"award-number":["P30 GM131959"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["5P20GM103444-07"],"award-info":[{"award-number":["5P20GM103444-07"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We describe a method to measure micron to millimeter displacement through tissue using an upconversion spectral ruler. Measuring stiffness (displacement under load) in muscles, bones, ligaments, and tendons is important for studying and monitoring healing of injuries. Optical displacement measurements are useful because they are sensitive and noninvasive. Optical measurements through tissue must use spectral rather than imaging approaches because optical scattering in the tissue blurs the image with a point spread function typically around the depth of the tissue. Additionally, the optical measurement should have low background and minimal intensity dependence. Previously, we demonstrated a spectral encoder using either X-ray luminescence or fluorescence, but the X-ray luminescence required an expensive X-ray source and used ionizing radiation, while the fluorescence sensor suffered from interference from autofluorescence. Here, we used upconversion, which can be provided with a simple fiber-coupled spectrometer with essentially autofluorescence-free signals. The upconversion phosphors provide a low background signal, and the use of closely spaced spectral peaks minimizes spectral distortion from the tissue. The small displacement noise level (precision) through tissue was 2 \u00b5m when using a microscope-coupled spectrometer to collect light. We also showed proof of principle for measuring strain on a tendon mimic. The approach provides a simple method to study biomechanics using implantable sensors.<\/jats:p>","DOI":"10.3390\/s21103554","type":"journal-article","created":{"date-parts":[[2021,5,20]],"date-time":"2021-05-20T06:13:45Z","timestamp":1621491225000},"page":"3554","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Upconversion Spectral Rulers for Transcutaneous Displacement Measurements"],"prefix":"10.3390","volume":"21","author":[{"given":"Melissa M.","family":"Suckey","sequence":"first","affiliation":[{"name":"Department of Chemistry, Clemson University, Clemson, SC 29634, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Donald W.","family":"Benza","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Clemson University, Clemson, SC 29634, USA"},{"name":"Department of Electrical and Computer Engineering, Clemson University, Clemson, SC 29634, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5850-5122","authenticated-orcid":false,"given":"John D.","family":"DesJardins","sequence":"additional","affiliation":[{"name":"Department of Bioengineering, Clemson University, Clemson, SC 29634, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9544-2367","authenticated-orcid":false,"given":"Jeffrey N.","family":"Anker","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Clemson University, Clemson, SC 29634, USA"},{"name":"Department of Bioengineering, Clemson University, Clemson, SC 29634, USA"},{"name":"Center for Optical Materials Science and Engineering (COMSET) and Environmental Toxicology Program, Clemson University, Clemson, SC 29634, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1016\/j.jse.2011.10.023","article-title":"Measurement of in vivo tendon function","volume":"21","author":"Bey","year":"2012","journal-title":"J. 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B"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/10\/3554\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:04:33Z","timestamp":1760162673000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/10\/3554"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,5,20]]},"references-count":43,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2021,5]]}},"alternative-id":["s21103554"],"URL":"https:\/\/doi.org\/10.3390\/s21103554","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,5,20]]}}}