<p>In this research, Se-doped ZnO-Al₂O₃ nanocomposite was synthesized using <i>Nymphaea Pygmaea alba</i> plant extract as nucleation and stabilizing agents. The synthesized nanocomposite underwent characterization for its physicochemical properties, including crystalline nature, size, morphology, and optical properties, utilizing procedures such as XRD, FT-IR, FESEM, and UV–Vis. XRD patterns confirmed the crystalline structure of the synthesized nanocomposite. FESEM images of the nanocomposite showed spherical morphology with an average size of about 21 nm. Additionally, the photocatalytic activity of the synthesized nanocomposite was thoroughly investigated for RhB dye degradation. Furthermore, to assess anticancer activity, the synthesized nanocomposite was tested on cancer CT26 and normal L929 cells via MTT assay, revealing increased cytotoxicity activity with higher concentrations of nanocomposite. The results of sensor studies showed that the synthesized nanocomposite showed high selectivity and sensitivity to Fe (III) ions with a correlation coefficient of R² ~ 0.9944. Therefore, the synthesized nanocomposite had satisfactory results in the detection of Fe (III) ions, which can be promising as a low-cost, highly sensitive, and selective sensor. Overall, this interdisciplinary investigation aims to enhance understanding of synthesized nanocomposite and their potential as multifunctional agents as sensors, photocatalysts, and anti-cancer.</p> Graphical Abstract <p></p>