{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,30]],"date-time":"2026-08-30T02:01:00Z","timestamp":1788055260057,"version":"build-2784847793"},"reference-count":26,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2025,10,25]],"date-time":"2025-10-25T00:00:00Z","timestamp":1761350400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Scientific and Technological Research Council of T\u00fcrkiye (T\u00dcB\u0130TAK) under the 2247-A National Outstanding Researchers Program","award":["121C270"],"award-info":[{"award-number":["121C270"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>COVID-19, caused by SARS-CoV-2, has created unprecedented global health challenges, necessitating rapid and reliable diagnostic strategies. The spike (S) protein, particularly its S1 subunit, plays a critical role in viral entry, making it a prime biomarker for early detection. In this study, we present a disposable, low-cost, and portable electrochemical biosensor employing specifically optimized aptamers (Optimers) for SARS-CoV-2 S1 recognition. The sensing approach is based on aptamer\u2013protein complex formation in solution, followed by immobilization onto pencil graphite electrodes (PGEs). The key parameters, including aptamer concentration, interaction time, redox probe concentration, and immobilization time, were systematically optimized by performing electrochemical measurement in redox probe solution containing ferri\/ferrocyanide using differential pulse voltammetry (DPV) technique.Under optimized conditions, the biosensor achieved an ultralow detection limit of 18.80 ag\/mL with a wide linear range (10\u22121\u2013104 fg\/mL) in buffer. Importantly, the sensor exhibited excellent selectivity against hemagglutinin antigen and MERS-CoV-S1 protein, while maintaining high performance in artificial saliva with a detection limit of 14.42 ag\/mL. Furthermore, its integration with a smartphone-connected portable potentiostat underscores strong potential for point-of-care use. To our knowledge, this is the first voltammetric biosensor utilizing optimized aptamers (Optimers) specific to SARS-CoV-2 S1 on disposable PGEs, providing a robust and field-deployable platform for early COVID-19 diagnostics.<\/jats:p>","DOI":"10.3390\/s25216579","type":"journal-article","created":{"date-parts":[[2025,10,29]],"date-time":"2025-10-29T05:48:46Z","timestamp":1761716926000},"page":"6579","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Smartphone-Integrated User-Friendly Electrochemical Biosensor Based on Optimized Aptamer Specific to SARS-CoV-2 S1 Protein"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4375-8386","authenticated-orcid":false,"given":"Arzum","family":"Erdem","sequence":"first","affiliation":[{"name":"Department of Analytical Chemistry, Faculty of Pharmacy, Ege University, 35040 \u0130zmir, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3268-8319","authenticated-orcid":false,"given":"Huseyin","family":"Senturk","sequence":"additional","affiliation":[{"name":"Department of Analytical Chemistry, Faculty of Pharmacy, Ege University, 35040 \u0130zmir, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Esma","family":"Yildiz","sequence":"additional","affiliation":[{"name":"Department of Analytical Chemistry, Faculty of Pharmacy, Ege University, 35040 \u0130zmir, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,10,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1400","DOI":"10.3390\/s80314000","article-title":"Electrochemical Biosensors\u2014Sensor Principles and Architectures","volume":"8","author":"Grieshaber","year":"2008","journal-title":"Sensors"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"132966","DOI":"10.1016\/j.cej.2021.132966","article-title":"Electrochemical Sensors for the Detection of SARS-CoV-2 Virus","volume":"430","author":"Kumar","year":"2022","journal-title":"Chem. 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