In recent years, the interest in environmentally friendly and sustainable methods for producing nanoparticles has grown significantly due to their potential benefits. Among these nanoparticles, selenium nanoparticles (SeNPs) have gained attention for their potential applications in biomedicine. This research sheds light on the feasibility of eco-friendly synthesis approaches for generating quercetin-coated selenium nanoparticles (DQSN) and their potential applications in the field of biomedicine. The main objective of this study is to develop a green synthesis technique for SeNPs using Diospyros ebenum extract as a natural reducing agent and quercetin as a capping agent. The synthesised nanoparticles were subjected to a range of characterisation techniques including UV–vis spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive x-ray analysis. The antioxidant assay was employed to evaluate nanoparticle's bioactivity. The results revealed the successful synthesis of DQSN with comprehensive characterisation confirming their morphology, crystallinity, functionalisation, elemental composition, size, and stability. In vitro, bioactivity studies demonstrated substantial antioxidant activity through DPPH radical scavenging. These findings underscore the potential utility of DQSN as promising candidates for biomedical applications; however, further extensive investigations are essential to ascertain their complete efficacy and toxicity profiles.