Silver selenide (Ag₂Se) is a promising nanomaterial due to its outstanding optoelectronic properties and countless bio-applications. To the best of our knowledge, we report, for the first time, a simple and easy method for the ultrasound-assisted synthesis of Ag₂Se nanoparticles (NPs) by mixing aqueous solutions of silver nitrate (AgNO₃) and selenous acid (H₂SeO₃) that act as Ag and Se sources, respectively, in the presence of dissolved fructose and starch that act as reducing and stabilizing agents, respectively. The concentrations of mono- and polysaccharides were screened to determine their effect on the size, shape and colloidal stability of the as-synthesized Ag₂Se NPs which, in turn, impact the optical properties of these NPs. The morphology of the as-synthesized Ag₂Se NPs was characterized by transmission electron microscopy (TEM) and both α- and β-phases of Ag₂Se were determined by X-ray diffraction (XRD). The optical properties of Ag₂Se were studied using UV–Vis spectroscopy and its elemental composition was determined non-destructively using scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). The biological activity of the Ag₂Se NPs was assessed using cytotoxic and bactericidal approaches. Our findings pave the way to the cost-effective, fast and scalable production of valuable Ag₂Se NPs that may be utilized in numerous fields.