Structural, Spectral, and Biological Investigations of Phytosynthesized Selenium-Doped CaO Nanoparticles: Experimental and Theoretical Studies

Environmentally benign Cassia angustifolia seed extract acts as a reducing and capping agent for the synthesis of phytomediated calcium oxide nanoparticles (CaO NPs) and selenium-doped calcium oxide nanoparticles (Se-CaO NPs). Whereas UV-DRS provides the bandgap with the change in absorbance on bare CaO and Se-CaO NPs, the FT-IR spectra corroborates the formation of NPs functionalized with phyto-groups. The XRD and Raman spectra that we obtain here provides insights into the lattice and phase changes of Se-CaO compared to the naked CaO NPs. The crystalline nature and average size are obtained as 30.33 and 18.82 nm for CaO NPs and Se-CaO NPs, respectively. The HRTEM and EDAX data obtained reveal the morphology, size, and elemental composition whereas XPS confirmed selenium structural integrity and its doping efficiency into the CaO matrix. Density functional theory (DFT)-based computational studies were carried out to elucidate the electronic structure, IR, and Raman spectra, revealing that selenium doping significantly alters the electronic density and charge transfer properties, which may account for its increased bioactivity. The Se-CaO NPs exhibited superior antimicrobial efficacy with effective minimum inhibitory concentrations (MIC: 7.8 –125 µg/mL) based on the distinct microbes. The cytotoxic effects of Se-CaO NPs on a Vero cell line (IC₅₀ = 175 ± 1.5 µg/mL) and MCF-7 breast cancer cells (IC50 = 53.2 ± 2.6 µg/mL) demonstrate their bioactivity and therapeutic efficacy. Hence, phytosynthesized Se-CaO NPs with bioactive surface capabilities promote environmental sustainability and dual-functionality potential toward microbes and cancer cells, paving a promising green route in nanomedicine.