Anti-cancer activity and optoelectronic properties via DFT calculations of rare-earth dually doped wurtzite-type ZnO nano-systems

The application of zinc oxide (ZnO) in the biomedical field and electronic devices is attributed to its physical and chemical properties. In this research, a comprehensive investigation was performed to explore the role of Eu and Dy dual-doping on the electronic structure, optical characteristics, and anti-cancer capability of ZnO. The structural analysis using the XRD experiment demonstrated the formation of a wurtzite hexagonal structured ZnO phase for the undoped sample. The crystal structure was maintained but with a slight distortion of the system with the co-doping effect. The crystallite size disclosed a reduction with increasing the co-doping concentration. TEM and EDX analysis proved the formation of the desired compositions. In the theoretical part, the density functional theory (DFT) is adopted to probe the electronic structure and optical characteristics of proposed samples. The band gap energy (E_g) of undoped ZnO is found to be 3.45 eV. For the dual-doped systems, the E_g values reduced progressively as the content of co-dopants increased. A prominent absorption peak revealed in the UV regime for the undoped ZnO is shifted to lower energies upon doping, implying the band gap reduction. DFT results demonstrate that the impurity states due to rare earth dopants are important for optic/electronic characteristics and can be harnessed to develop photoelectric devices. According to the anti-cancer in vitro analysis, the prepared nanoparticles show strong cytotoxicity against HeLa and HCT-116 cells. The cell viability for colon cancer HCT-116 cells was C0 (37.18 %), C1 (31.96 %), C2 (64.27 %) and C3 (58.12 %), and the cell viability for cervical cancer HeLa cells was C0 (39.05 %), C1 (42.30 %), C2 (57.68 %), and C3 (45.29 %). Furthermore, DAPI staining indicated that the treatment with the Eu and Dy dual-doped ZnO NPs produced a cancer apoptotic cell death. The results of this work will be useful for further examination and choosing the appropriate nanomaterials for the targeted fields of applications.