Display omitted •Elemental content of P. longum catkin were analyzed by ICP-OES and ICP-MS.•PLAgNPs, PLCuONPs, and PLNiNPs were synthesized under different conditions.•P. longum catkin has shown toxic elements content below the permissible ranges.•PLNPs showed significant cytotoxicity against DU-145 prostate cancer cell line.•PLNPs exhibited potent antioxidant, antimicrobial, and catalytic activities. Piper longum (long pepper) in dried form is used in several traditional medicines and as a spice. The present study highlights nutritional and toxic elements content, synthesis, and characterization of silver, copper oxide, and nickel nanoparticles using P. longum catkin extract. The study also determined anticancer, antioxidant, antimicrobial, and redox catalytic activities of the synthesized NPs. The P. longum extract mediated nanoparticles (PLNPs) synthesized at different pH and ratios were characterized by UV–Vis (ultra-violet-visible), FT-IR (Fourier-Transform infrared), and scanning electron and atomic force microscopic (SEM, AFM) techniques. Elemental content of P. longum catkin determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ICP-mass spectrometry (ICP-MS) indicated appreciable concentrations of nutritional elements, and well below permissible ranges of toxic elements. Well-defined and stable silver nanoparticles (PLAgNPs) were formed in 1:4 to 1:6 ratios, while copper oxide and nickel NPs (PLCuONPs and PLNiNPs) were found prominent in 1:6 ratio. In determining the effect of pH on synthesized PLNPs, sharp intense absorption peaks were obtained under slightly neutral to highly basic conditions (pH 6 to 13) for PLAgNPs, whereas for PLCuONPs and PLNiNPs, pH 7–8 was optimum. In biological activities, PLNPs exhibited significant anticancer efficacy against DU-145 (prostate cancer) cell line in the range from 92.7% (PLCuONPs) to 100% (PLAgNPs, PLNiNPs). Fuurthermore, the sythesized NPs exhibited significant antioxidant, antimicrobial, and redox catalytic properties. This study concluded the promising nutritional, biological and environmental remediation applications, and hence, further exploration of the synthesized NPs in biological and clinical applications is currently under investigation.