Bovine serum albumin (BSA)-protected AgPt bimetallic nanoparticles have been synthesized through a galvanic replacement reaction, using a silver nanoprism as a template. Synthesis was performed without the use of synthetic chemical surfactants, using proteins as a surface coating. Structural and compositional characterizations were performed using several spectroscopic and microscopic techniques. The protein-protected AgPt nanoparticles show effective pH-switchable enzyme mimicking (“nanozyme”) activity similar to catalase and peroxidase. The platinum content in the AgPt nanoparticles is playing an important role in determining the enzymatic catalysis rate of the nanoparticles. Because of their porous structure, molecular payloads such as calcein also can be incorporated into the AgPt nanoparticles, which can be released on demand by chemical triggers, such as hydrogen peroxide.