(a) The separation of bacteria by vancomycin conjugated Fe ₃ O ₄ /DOPA/Van nanoparticles and (b) H-bonding interactions between the vancomycin molecule and the d -alanyl- d -alanine dipeptide of the bacterial surface.

Surface active amine-functionalized silica coated magnetic iron oxide nanoparticles were prepared by a simple two-step process for adsorbing CO₂ gas from aqueous medium. First, oleic acid (OA) coated iron oxide magnetic particles (denoted as Fe₃O₄-OA) were prepared by a simple coprecipitation method. Then, the surface of the Fe₃O₄-OA particles was coated with silica by using tetraethyl orthosilicate. Finally, aminated Fe₃O₄/SiO₂-NH₂ nanoparticles were concomitantly formed by the reactions of 3-aminopropyl triethoxysilane with silica-coated particles. The formation of materials was confirmed by Fourier transform infrared spectral analysis. Transmission electron microscopic analysis revealed both spherical and needle-shaped morphologies of magnetic Fe₃O₄/SiO₂-NH₂ particles with an average size of 15 and 68.6 nm, respectively. The saturation magnetization of Fe₃O₄/SiO₂-NH₂ nanoparticles was found to be 33.6 emu g^-1, measured by a vibrating sample magnetometer at ambient conditions. The crystallinity and average crystallite size (7.0 nm) of the Fe₃O₄/SiO₂-NH₂ particles were revealed from X-ray diffraction data analyses. Thermogravimetric analysis exhibited good thermal stability of the nanoadsorbent up to an elevated temperature. Zeta potential measurements revealed pH-sensitive surface activity of Fe₃O₄/SiO₂-NH₂ nanoparticles in aqueous medium. The produced magnetic Fe₃O₄/SiO₂-NH₂ nanoparticles also exhibited efficient proton capturing activity (92%). The particles were used for magnetically recyclable adsorption of aqueous CO₂ at different pH values and temperatures. Fe₃O₄/SiO₂-NH₂ nanoparticles demonstrated the highest aqueous CO₂ adsorption efficiency (90%) at 40 °C, which is clearly two times higher than that of nonfunctionalized Fe₃O₄-OA particles.

Functionalized iron oxide nanoparticles (IONPs) have unique physical and chemical properties, which make them potential candidates for biomedical applications. In this study, a facile one-pot method is reported for the preparation of poly(acrylic acid) (PAA) functionalized IONPsthrough in situ free radical solution polymerization of AA and subsequent coprecipitation of Fe³⁺ and Fe²⁺ ions. The FTIR spectroscopic and TGA results indicated the successful formation and surface functionalization of IONPs with PAA. Electron micrographs showed that the prepared particles were of nano-sized and their shape is dependent on the concentration of PAA. pH-dependent variation of average hydrodynamic diameter confirmed the pH-responsivity of PAA-functionalized IONPs. Magnetic measurement suggested that the PAA functionalized IONPs were strongly paramagnetic (53.0 emug⁻¹). Fenton-like catalytic generation is carried out to measure toxicity associated with the nanoparticles. The suppression ability for reactive oxygen species (ROS) generation associated with PAA-functionalized IONPs was studied via methylene blue degradation assay to address their toxicity profile. PAA-functionalized IONPs exhibited better suppression ability than that of the bare IONPs. The adsorption behavior of trypsin was also studied at different pH levels and a maximum adsorption is occurred on PAA-functionalized IONPs at pH 5.0. Catalytic behavior study confirmed higher activity of trypsin immobilized on PAA-functionalized IONPs than that of the reference IONPs. Therefore, the functionalized IONPs can be of high interest for magnetically recyclable biocatalyst carrier.

Multifunctional nanocomposites that integrate lanthanide photophysics with iron oxide magnetism represent a rapidly expanding class of materials for precision bioimaging and theranostics. Lanthanide-based iron oxide nanoparticles (Ln-IONPs) uniquely combine the narrow f–f emissions, long-lived excited states, and UC/DC luminescence of lanthanides with the superparamagnetism, high relaxivity, and magnetic field responsiveness of Fe₃O₄/γ-Fe₂O₃. However, their rational design remains challenging due to interfacial energy transfer, concentration-dependent cross-relaxation, and fluorescence quenching induced by iron oxide. This review provides the first systematic overview of Ln-IONPs, covering their fundamental luminescent and magnetic mechanisms, ligand and host engineering, and factors influencing their optical and magnetic performance, such as particle size, dopant distribution, surface chemistry, pH, temperature, and solvent effects. Synthetic strategies, including coprecipitation, thermal decomposition, hydro(solvo)thermal growth, sol–gel assembly, microwave-mediated crystallization, and polymer-integrated architectures, are critically evaluated with respect to phase control, heterointerface engineering, and quenching suppression via inert buffer layers. We further highlight recent advances in multimodal bio-applications, including high-resolution UC imaging, magnetically guided drug delivery, photothermal/photodynamic therapy, and integrated opto-magnetothermal theranostics. Persistent challenges, such as optimizing core–shell energy barriers, balancing luminescence efficiency with magnetic moment retention, and improving in vivo stability and clearance, are discussed alongside future opportunities for designing next-generation Ln-IONPs with enhanced optical–magnetic coupling and clinical translational potential.