A novel approach to the photochemical UV-C activation of PAA-coated Fe₃O₄ nanoparticles for oriented APTES functionalisation with free surface-amino groups

• Fe₃O₄ nanoparticles with polyhedral and cubic morphologies were synthesised by thermal decomposition. • A novel method was used for surface modification of Fe 3 O 4 @PAA MNPs with APTES. • ATR-FTIR and XPS confirmed successful ligand attachment; zeta potential shifted from negative to positive. • RNA extraction efficiency of modified nanoparticles was comparable to SiO₂-coated MNPs commonly used in commercial-like kits. Fe₃O₄ MNPs with polyhedral ( P1 ) and cubic ( K1 ) morphologies, prepared by a thermal decomposition method, were coated with polyacrylic acid (PAA) and surface functionalised with the organic ligand 3-(aminopropyl)triethoxysilane (APTES). A novel method was used to attach APTES to polyacrylic acid, where we used photochemical activation of the PAA layer by UV-C (254 nm). The novelty of this work lies in the simple yet unique UV-C activation of surface oxyl groups to achieve oriented APTES functionalisation. The surface functionalisation, together with controlled nanoparticle morphology, was intended to improve the affinity of magnetic nanoparticles (MNPs) for nucleic acids and thus facilitate efficient nucleic acid separation. Structural and surface characterisation was performed using XRD, SEM, ATR-FTIR, XPS, and zeta potential analysis, confirming the successful modification of the surface of nanoparticles with APTES. SQUID magnetometry analysis demonstrated morphology-dependent magnetic response. Polyhedral Fe₃O₄ nanoparticles exhibited a higher saturation magnetisation (∼90 Am² kg⁻¹) compared to their cubic counterparts (∼70 Am² kg⁻¹), reflecting differences in magnetic anisotropy and structural ordering. Both morphological variants show the Verwey transition near 120 K, indicative of high crystallinity and phase purity of the magnetite core. Magnetic measurements using SQUID magnetometry revealed multidomain behaviour at room temperature, essential for magnetic separation applications. RNA extraction tests demonstrated that P1 and K1 nanoparticles exhibited separation efficiency that is comparable to spherical Fe₃O₄@SiO₂ particles used in commercial kits, despite lacking a silica layer. These findings highlight the potential of Fe₃O₄ MNPs with diverse morphology and ligand-functionalised nanoparticles as the basis for next-generation nucleic acid isolation systems for different advanced biomedical applications.