{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,15]],"date-time":"2026-03-15T05:56:10Z","timestamp":1773554170969,"version":"3.50.1"},"reference-count":36,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T00:00:00Z","timestamp":1773360000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The ability to assess molecular binding kinetics in real time is critical for advancing our understanding of molecular interactions in biochemical and biotechnological systems. This work presents a novel optical tweezer (OT)-based method to monitor molecular affinity in real time, focusing on the high-affinity streptavidin\u2013biotin system as a model. Transparent poly(methyl methacrylate) (PMMA) microparticles functionalized with streptavidin were trapped before, during, and after binding with biotinylated bovine serum albumin (biotin\u2013BSA), enabling the analysis of forward-scattered signals to detect nanoscale changes in particle size. By applying the Power Spectral Density method, the friction coefficient of individual particles was calculated, allowing for real-time tracking of binding dynamics and the estimation of the association rate constant (kon\u2248106M\u22121s\u22121). These results are consistent with literature values and demonstrate the potential of this OT-based approach for non-invasive, label-free detection of molecular interactions. Compared to existing techniques, such as atomic force microscopy and cantilever-based sensors, this method offers significant advantages, including real-time monitoring, adaptability to different bioaffinity systems, and compatibility with miniaturized setups. This work establishes a foundation for using OT-based tools to monitor high-affinity molecular interactions in real time. While demonstrated here using biotinylated BSA as a model ligand, future studies will explore the method\u2019s applicability to smaller ligands and more subtle surface modifications.<\/jats:p>","DOI":"10.3390\/s26061814","type":"journal-article","created":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T11:12:25Z","timestamp":1773400345000},"page":"1814","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Real-Time Probing of Molecular Affinity Using Optical Tweezers"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-4721-385X","authenticated-orcid":false,"given":"Joana","family":"Teixeira","sequence":"first","affiliation":[{"name":"Center for Applied Photonics, INESC TEC, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"},{"name":"Departamento de F\u00edsica e Astronomia, Faculdade de Ci\u00eancias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6421-9763","authenticated-orcid":false,"given":"Jos\u00e9 A.","family":"Ribeiro","sequence":"additional","affiliation":[{"name":"CIQUP\/IMS, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5928-5598","authenticated-orcid":false,"given":"Marcus","family":"Monteiro","sequence":"additional","affiliation":[{"name":"CIQUP\/IMS, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8467-4357","authenticated-orcid":false,"given":"Nuno A.","family":"Silva","sequence":"additional","affiliation":[{"name":"Center for Applied Photonics, INESC TEC, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"},{"name":"Departamento de F\u00edsica e Astronomia, Faculdade de Ci\u00eancias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1484-2068","authenticated-orcid":false,"given":"Pedro A. S.","family":"Jorge","sequence":"additional","affiliation":[{"name":"Center for Applied Photonics, INESC TEC, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"},{"name":"Departamento de F\u00edsica e Astronomia, Faculdade de Ci\u00eancias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"5800","DOI":"10.1039\/c2cs35162e","article-title":"Molecular recognition: From solution science to nano\/materials technology","volume":"41","author":"Ariga","year":"2012","journal-title":"Chem. Soc. Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1002\/anie.198800891","article-title":"Supramolecular chemistry\u2014Scope and perspectives molecules, supermolecules, and molecular devices (Nobel lecture)","volume":"27","author":"Lehn","year":"1988","journal-title":"Angew. Chem. Int. Ed. 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