Sustainable biogenic synthesis of copper nanoparticles using Glycine max calli and their circular role in callus regeneration.

The biosynthesis of metallic nanoparticles through plant-based systems provides a sustainable and environmentally friendly alternative to conventional chemical routes. In this study, residual soybean (Glycine max) callus tissues, derived from previous tissue culture experiments, were repurposed as reducing and stabilizing agents for the rapid synthesis of copper nanoparticles (CuNPs). Using high-intensity ultrasound (CupHorn), CuNPs were successfully obtained in only 8 min, representing a substantial reduction in reaction time compared to traditional green synthesis methods. The proposed route was assessed using the AGREEprep tool, achieving a score of 0.68 (on a 0-1 scale), indicative of strong compliance with the principles of green chemistry due to low energy demand, minimal waste generation, and the use of safe reagents. In contrast, conventional biosynthesis methods typically range between 0.22 and 0.24. Post-synthesis purification via dialysis under basic pH efficiently removed residual organic matter. The resulting nanoparticles were characterized by UV-Vis, DLS, and TEM, confirming the formation of metallic CuNPs with an average size of ~ 10 nm, uniform morphology, and high colloidal stability (zeta potential of + 60 mV). Complementary Raman and FTIR analyses further confirmed the metallic copper structure (Cu⁰). Application of purified CuNPs (1 µg L⁻