Green synthesis of Fe₃O₄ nanoplatforms via Camellia sinensis: Linking surface chemistry, membrane interactions, and...

The rational design of magnetic nanoplatforms requires a thorough understanding of their structure, surface chemistry, and behavior at biological interfaces. Herein, iron oxide nanoparticles functionalized in situ with Camellia sinensis extract (Fe₃O₄-CS) were synthesized via a green one-pot route and comprehensively characterized. XRD revealed a cubic inverse spinel iron oxide structure, with an average crystallite size smaller than 13 nm. FTIR, Raman spectroscopy, and TGA demonstrated successful phytochemical capping, while DLS and zeta potential measurements (-24 mV) revealed changes in the interfacial properties of the nanoplatforms.VSM revealed magnetically soft behavior at room temperature, with low remanence and coercivity, presenting 62 emu g^-1 for pure Fe₃O₄, and varying between 6 emu g^-1 (Fe₃O₄-CS.150) and 42 emu g^-1 (Fe₃O₄-CS.25) for the coated nanoplatforms. Preliminary in vitro biological assays showed high cell viability in human peripheral blood mononuclear cells (PBMCs) (>85%) and a reduction in metabolic viability in Ehrlich Ascites Tumor (EAT) cells, reaching a minimum of approximately 62% under the tested conditions. At the air-water interface, Fe₃O₄-CS.75 exhibited a carrier-mediated multivalent effect, increasing the maximum insertion pressure (MIP) into DPPC Langmuir monolayers from 41.5 mN m^-1 for the free extract to 72.2 mN m^-1, exceeding the lateral pressure of biological membranes. Brewster Angle Microscopy and interfacial dilatational rheology revealed that nanoparticle insertion promoted local monolayer condensation without disrupting its dynamic viscoelastic behavior. These findings establish a clear relationship between green surface functionalization, physicochemical properties, and membrane interactions, highlighting Fe₃O₄-CS as a promising magnetic nanoplatform for future biomedical applications.