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The prepared NSCDs presented a selective dual optical response to Cu(II) in water through the arising of an absorption band at 660 nm and simultaneous fluorescence enhancement at 564 nm. The first effect was attributed to formation of cuprammonium complexes through coordination with amino functional groups of NSCDs. Alternatively, fluorescence enhancement can be explained by the oxidation of residual OPD bound to NSCDs. Both absorbance and fluorescence showed a linear increase with an increase of Cu(II) concentration in the range 1\u2013100 \u00b5M, with the lowest detection limit of 100 nM and 1 \u00b5M, respectively. NSCDs were successfully incorporated in a hydrogel agarose matrix for easier handling and application to sensing. The formation of cuprammonium complexes was strongly hampered in an agarose matrix while oxidation of OPD was still effective. As a result, color variations could be perceived both under white light and UV light for concentrations as low as 10 \u00b5M. Since these color changes were similarly perceived in tap and lake water samples, the present method could be a promising candidate for simple, cost-effective visual monitoring of copper onsite.<\/jats:p>","DOI":"10.3390\/s23063029","type":"journal-article","created":{"date-parts":[[2023,3,13]],"date-time":"2023-03-13T03:28:33Z","timestamp":1678678113000},"page":"3029","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Colorimetric and Fluorescent Sensing of Copper Ions in Water through o-Phenylenediamine-Derived Carbon Dots"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6319-2519","authenticated-orcid":false,"given":"Roberto","family":"Pizzoferrato","sequence":"first","affiliation":[{"name":"Department of Industrial Engineering, University of Rome Tor Vergata, 00133 Rome, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8384-4724","authenticated-orcid":false,"given":"Ramanand","family":"Bisauriya","sequence":"additional","affiliation":[{"name":"Department of Industrial Engineering, University of Rome Tor Vergata, 00133 Rome, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9053-0587","authenticated-orcid":false,"given":"Simonetta","family":"Antonaroli","sequence":"additional","affiliation":[{"name":"Department of Chemical Sciences and Technology, University of Rome Tor Vergata, 00133 Rome, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0159-3974","authenticated-orcid":false,"given":"Marcello","family":"Cabibbo","sequence":"additional","affiliation":[{"name":"Department of Industrial Engineering and Mathematical Sciences (DIISM), Universit\u00e0 Politecnica Delle Marche, 60131 Ancona, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3285-4919","authenticated-orcid":false,"given":"Artur J.","family":"Moro","sequence":"additional","affiliation":[{"name":"LAQV-REQUIMTE, Departamento de Qu\u00edmica, CQFB, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"47","DOI":"10.1016\/j.biotechadv.2015.12.001","article-title":"Progress in the biosensing techniques for trace-level heavy metals","volume":"34","author":"Mehta","year":"2016","journal-title":"Biotechnol. 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