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This sensing platform relies on an electrode\u2010bound, redox\u2010reporter\u2010modified aptamer. The electrochemical signal is thought to originate from the aptamer undergoing a binding\u2010induced conformational change capable of moving the redox reporter closer to the electrode surface. While this is the generally accepted mechanism, it is notable that there is limited evidence demonstrating conformational change or distance\u2010dependent change in electron transfer rates in E\u2010AB sensors. In response, we investigate here the signal transduction of the well\u2010studied cocaine\u2010binding aptamer with different analytical methods and found that this sensor relies on a redox\u2010reporter \u2010 ligand competition mechanism rather than a ligand\u2010induced structure formation mechanism. Our results show that the covalently bound redox reporter, methylene blue, binds at or near the ligand binding site on the aptamer resulting in a folded conformation of the cocaine\u2010binding aptamer. Addition of ligand then competes with the redox reporter for binding, altering its electron transfer rate. While we show this for the cocaine\u2010binding aptamer, given the prevalence of methylene blue in E\u2010AB sensors, a similar competition\u2010based may occur in other systems.<\/jats:p>","DOI":"10.1002\/chem.202300618","type":"journal-article","created":{"date-parts":[[2023,3,29]],"date-time":"2023-03-29T08:38:13Z","timestamp":1680079093000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":31,"title":["Redox Reporter \u2010 Ligand Competition to Support Signaling in the Cocaine\u2010Binding Electrochemical Aptamer\u2010Based Biosensor"],"prefix":"10.1002","volume":"29","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0490-7115","authenticated-orcid":false,"given":"Philippe","family":"Dauphin\u2010Ducharme","sequence":"first","affiliation":[{"name":"D\u00e9partement de chimie Universit\u00e9 de Sherbrooke  Sherbrooke QC J1K 2R1 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zachary R.","family":"Churcher","sequence":"additional","affiliation":[{"name":"Chemistry Department York University  4700 Keele Street Toronto Ontario M3J 1P3 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5580-1273","authenticated-orcid":false,"given":"Aron A.","family":"Shoara","sequence":"additional","affiliation":[{"name":"Chemistry Department York University  4700 Keele Street Toronto Ontario M3J 1P3 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1982-8177","authenticated-orcid":false,"given":"Erfan","family":"Rahbarimehr","sequence":"additional","affiliation":[{"name":"D\u00e9partement de chimie Universit\u00e9 de Sherbrooke  Sherbrooke QC J1K 2R1 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sladjana","family":"Slavkovic","sequence":"additional","affiliation":[{"name":"Chemistry Department York University  4700 Keele Street Toronto Ontario M3J 1P3 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7623-475X","authenticated-orcid":false,"given":"Nicolas","family":"Fontaine","sequence":"additional","affiliation":[{"name":"D\u00e9partement de chimie Universit\u00e9 de Sherbrooke  Sherbrooke QC J1K 2R1 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Olivia","family":"Boisvert","sequence":"additional","affiliation":[{"name":"D\u00e9partement de chimie Universit\u00e9 de Sherbrooke  Sherbrooke QC J1K 2R1 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5573-4891","authenticated-orcid":false,"given":"Philip E.","family":"Johnson","sequence":"additional","affiliation":[{"name":"Chemistry Department York University  4700 Keele Street Toronto Ontario M3J 1P3 Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2023,5,5]]},"reference":[{"key":"e_1_2_9_1_1","first-page":"805","volume-title":"Electrochemical Methods: Fundamentals and Applications","author":"Bard A. 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