Environmentally benign, stable quantum dot size spherical Cu particles with an average size of ∼ 4.5 nm, as measured via transmission electron microscope, were coherently tailored exploiting renewable ethno‐pharmacological Oxalis corniculata plant extract as both reducing plus capping agent. The reliable green aqueous synthesis approach completely excluded the usage of inert atmosphere and harmful chemicals including organic solvents. The ensuing cost effective Cu nanoparticles exhibited excellent intrinsic peroxidase like activity and superior nanozyme behaviour compare to earlier reports with Km value of 0.01426 M and rmax equal to 0.1399 Mmin−1 toward the oxidation of peroxidase substrate H2O2 in presence of o‐phenylenediamine, a paradigm reaction. Significantly, the as‐prepared Cu particles have been proven to be a novel catalyst for feasible selective aqueous phase conversion of fructose to levulinic acid with a maximum yield of ∼ 22.38% at 90°C in the absenteeism of prominent side product(s), auxiliaries and high temperature reaction condition. Lewis acid property and large surface area of the generated nanoscale particles attributed to their excellent catalytic potential introducing a new avenue in the continuous demand for better sensing, biomedical applications and cleaner energy production.