Comparative evaluation of green-synthesized CeO2-rich and multi-rare-earth-containing oxide-rich nanoparticles prepared using Moringa oleifera seed extract: physicochemical characterization and preliminary cell-free screening.

Fresh aqueous extracts were independently prepared from the same collected Moringa oleifera seed lot and used as biogenic media for the paired preparation of CeO2-rich nanoparticles (CeO2 NPs) and Ce-rich, multi-rare-earth-containing oxide-rich nanoparticles (multi-REO NPs). Three independent synthesis batches were prepared for each nanoparticle system under standardized extraction and harmonized reaction and post-synthesis conditions. The physicochemical properties of both nanoparticle systems were investigated using UV-vis spectroscopy, FTIR, XRD, SEM, EDS analysis/mapping, TEM/SAED, DLS, and zeta-potential measurements, while HPLC profiling was performed to characterize the phytochemical constituents of the M. oleifera seed extract. TEM analysis showed that CeO2 NPs were predominantly quasi-spherical, with projected particle dimensions of approximately 5-15 nm, whereas multi-REO NPs exhibited larger projected particle dimensions of approximately 20-60 nm. Multi-REO NPs also exhibited more numerous and comparatively better-resolved diffraction features based on XRD and TEM-SAED analyses. Zeta-potential measurements revealed stronger electrostatic stabilization for CeO2 NPs (-25.5 mV) than for multi-REO NPs (-5.09 mV). Multi-REO NPs generally produced greater apparent cell-free assay responses than CeO2 NPs at equivalent concentrations. Multi-REO NPs exhibited estimated IC50 values of 115.3 and 88.2 µg mL-1 for DPPH˙ and ABTS˙+ scavenging, respectively, compared with 71.4 and 55.5 µg mL-1 for ascorbic acid. The estimated IC50 values were 129.1 µg mL-1 for α-amylase inhibition, compared with 79.57 µg mL-1 for acarbose, and 159.6 µg mL-1 for BSA thermal-denaturation inhibition, compared with 121.5 µg mL-1 for diclofenac sodium. CeO2 NPs did not reach 50% response within the tested range for these endpoints, whereas neither nanoparticle system exhibited a monotonic concentration-dependent AChE-inhibitory response. Overall, the two compositionally distinct nanoparticle systems exhibited different physicochemical, colloidal, and assay-specific profiles, with multi-REO NPs generally showing greater cell-free responses. However, the findings do not establish rare-earth synergy, biological safety, or therapeutic efficacy, and require further mechanistic, interference-control, cytotoxicity, cellular, and in vivo evaluation.