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In this work, porphyrins bearing amine (PNH2) or carboxyl (PCOOH) groups were covalently conjugated onto functionalized SiNP surfaces via carbodiimide-mediated amide coupling, yielding the silica\u2013porphyrin nanohybrids H-PNH2 and H-PCOOH. Successful surface functionalization was confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Photophysical studies demonstrated that both nanohybrids retained efficient singlet oxygen (1O2) generation. In vitro biological assays revealed a strong dependence of photodynamic activity on the nature of the conjugated porphyrin, with H-PCOOH exhibiting markedly enhanced photocytotoxicity with respect to the free porphyrins, while H-PNH2 showed an attenuated light-dose response. Notably, H-PCOOH induced pronounced cell death at low light doses (1 J\/cm2), with a half-maximal inhibitory concentration (IC50) below 0.3 \u00b5M. These findings highlight the potential of silica\u2013porphyrin nanohybrids as efficient photosensitizers for PDT applications.<\/jats:p>","DOI":"10.3390\/ijms27052380","type":"journal-article","created":{"date-parts":[[2026,3,4]],"date-time":"2026-03-04T13:11:36Z","timestamp":1772629896000},"page":"2380","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Covalently Surface-Functionalized Porphyrins on Silica Nanoparticles for Efficient Photodynamic Therapy"],"prefix":"10.3390","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2381-4694","authenticated-orcid":false,"given":"Daniel S.","family":"Cavaco","sequence":"first","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Institute of Molecular Sciences, and Departamento de Engenharia Qu\u00edmica, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"given":"Maria Jo\u00e3o","family":"\u00c1lvaro-Martins","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Institute of Molecular Sciences, and Departamento de Engenharia Qu\u00edmica, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"given":"Mafalda","family":"Domingues","sequence":"additional","affiliation":[{"name":"iBB\u2014Institute for Bioengineering and Biosciences, and Associate Laboratory i4HB\u2014Institute for Health and Bioeconomy, and DBE-Department of Bioengineering, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"given":"Tiago","family":"Palmeira","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Institute of Molecular Sciences, and Departamento de Engenharia Qu\u00edmica, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3205-9459","authenticated-orcid":false,"given":"Sandra N.","family":"Pinto","sequence":"additional","affiliation":[{"name":"iBB\u2014Institute for Bioengineering and Biosciences, and Associate Laboratory i4HB\u2014Institute for Health and Bioeconomy, and DBE-Department of Bioengineering, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1624-6825","authenticated-orcid":false,"given":"Leandro M. O.","family":"Louren\u00e7o","sequence":"additional","affiliation":[{"name":"LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2302-9661","authenticated-orcid":false,"given":"Gil","family":"Gon\u00e7alves","sequence":"additional","affiliation":[{"name":"Centre for Mechanical Technology and Automation (TEMA), University of Aveiro, 3810-193 Aveiro, Portugal"},{"name":"Intelligent Systems Associate Laboratory (LASI), 4800-058 Guimar\u00e3es, Portugal"}]},{"given":"Carla I. M.","family":"Santos","sequence":"additional","affiliation":[{"name":"Centro de Qu\u00edmica Estrutural, Institute of Molecular Sciences, and Departamento de Engenharia Qu\u00edmica, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"},{"name":"LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8506-7025","authenticated-orcid":false,"given":"Ermelinda M. 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