The design of highly active nanozymes and the establishment of ultra-sensitive bioassays remain a challenge. Therefore, it is necessary to synthesize highly active nanozymes. In this work, a Pd-Pt-Ru (PPR) nanozyme was prepared by atomic coating of the bimetallic nanozyme Pd-Pt. The steady-state kinetics showed that the PPR nanozyme had excellent peroxidase-like activity. Based on this concept, the as-prepared PPR nanozyme was applied to the detection of ascorbic acid (AA) and hydrogen peroxide (H2O2). The linear ranges for ascorbic acid and hydrogen peroxide were 2-12 μM and 5-40 mM, respectively. The limits of detection (LOD) are 1.13 μM and 2.79 mM, respectively. Ascorbic acid was used as a typical model to assay the total antioxidant capacity (TAC) of foods and several herbs. The Fructus Corni extract showed the highest reducing ability. The corresponding extracts were applied for the green synthesis of silver nanoparticles with a size of 167 nm. This study provides a method for the design of highly active nanozymes and the expansion of their applications.