We report a type of polymer microgel that can undergo a rapid and highly sensitive volume change upon adding H2O2. Such a H2O2-sensitive microgel is made of dextrantyramine and horseradish peroxidase (HRP), which are interpenetrated in chemically cross-linked gel networks of poly(oligo(ethylene glycol) methacrylates). Unlike the H2O2-sensitive microgels reported in previous arts that typically involve degradation processes related to H2O2-induced cleavability of specific bonds, the proposed microgels can shrink upon adding H2O2 owing to the HRP-catalyzed coupling reaction of tyramine residues via decomposition of H2O2. While a fast (<10 s) and stable shrinkage of the microgels can be reached upon adding H2O2 over a concentration range 50.0 mu M1.0 mM, the response time can be modulated by the dispersion temperature in a nonmonotonous way over 1038 degrees C. With the microgels as probes, the H2O2 detection limit was approximately 6.8 ?M. In a combined use of the microgels with glucose oxidase for glucose detection, the glucose detection limit was approximately 83.1 mu M.