{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,7]],"date-time":"2026-03-07T15:44:53Z","timestamp":1772898293967,"version":"3.50.1"},"reference-count":39,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2026,1,2]],"date-time":"2026-01-02T00:00:00Z","timestamp":1767312000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>The formation of interfacial charge transfer (ICT) complexes between phenolic ligands and metal oxide surfaces enables surface functionalization strategies with potential applications in catalysis and bioconjugation. In this study, magnetite (Fe3O4) nanoparticles were modified with two phenolic ligands, 5-aminosalicylic acid (5ASA) and caffeic acid (CA), to generate ICT complexes capable of covalent or non-covalent enzyme immobilization, respectively. The modified nanomaterials were structurally characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). Horseradish peroxidase (HRP) was immobilized on these functionalized supports using varying nanoparticle amounts (10\u201330 mg) and initial enzyme concentrations (25\u2013250 \u00b5g mL\u22121). Catalytic activity was evaluated using pyrogallol oxidation assays. The Fe3O4\/5ASA\u2013HRP system exhibited a maximum activity of 2.5 U per 20 mg of support (approximately 125 U g\u22121), whereas Fe3O4\/CA showed minimal activity under the same conditions. Enzyme loading studies confirmed that 5ASA-enabled covalent attachment resulted in significantly higher immobilization efficiency (up to 1068 mg g\u22121) compared to the CA system. Reusability tests demonstrated that the Fe3O4\/5ASA system retained high absolute catalytic activity during the initial reaction cycles and consistently outperformed the non-covalently immobilized Fe3O4\/CA system upon repeated reuse. The magnetic properties of Fe3O4 allowed rapid recovery of the biocatalysts using an external magnetic field. These results highlight the effectiveness of ICT-based functionalization for enzyme immobilization, positioning Fe3O4\/5ASA as a promising platform for robust and reusable biocatalysts in environmental and industrial applications.<\/jats:p>","DOI":"10.3390\/molecules31010178","type":"journal-article","created":{"date-parts":[[2026,1,2]],"date-time":"2026-01-02T09:56:23Z","timestamp":1767347783000},"page":"178","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Magnetically Recoverable ICT-Functionalized Fe3O4 Nanoparticles for Efficient Horseradish Peroxidase Immobilization"],"prefix":"10.3390","volume":"31","author":[{"given":"Katarina","family":"Isakovi\u0107","sequence":"first","affiliation":[{"name":"Vin\u010da Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Centre of Excellence for Photoconversion, University of Belgrade, 11001 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9494-6766","authenticated-orcid":false,"given":"Marko","family":"Jonovi\u0107","sequence":"additional","affiliation":[{"name":"Institute of Chemistry, Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Du\u0161an","family":"Sredojevi\u0107","sequence":"additional","affiliation":[{"name":"Vin\u010da Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Centre of Excellence for Photoconversion, University of Belgrade, 11001 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marko","family":"Bo\u0161kovi\u0107","sequence":"additional","affiliation":[{"name":"Laboratory for Theoretical and Condensed Matter Physics, Vin\u010da Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, 11001 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4683-0603","authenticated-orcid":false,"given":"Jovana","family":"Peri\u0161a","sequence":"additional","affiliation":[{"name":"Vin\u010da Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Centre of Excellence for Photoconversion, University of Belgrade, 11001 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3009-1698","authenticated-orcid":false,"given":"Zorica","family":"Kne\u017eevi\u0107-Jugovi\u0107","sequence":"additional","affiliation":[{"name":"Department of Biochemical Engineering and Biotechnology, Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6440-6577","authenticated-orcid":false,"given":"Vesna","family":"Lazi\u0107","sequence":"additional","affiliation":[{"name":"Vin\u010da Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Centre of Excellence for Photoconversion, University of Belgrade, 11001 Belgrade, Serbia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Lazi\u0107, V., and Nedeljkovi\u0107, J.M. 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