Nature is greatly capable of providing inspiration for the novel design of functional materials. Herein, the efficient bioreactors’ construction of pollen grains inspires us to mimic them for superior gas sensing application. By developing a facile two-step soakage process and subsequent calcinations, the bioreactors are mimicked fully: (I) biosensitive pollen coats on pollen grains are replaced by gas sensitive tin oxide (SnO₂) coats, and (II) the fine hierarchical scaffolds are maintained by the self-support of newly formed SnO₂ coats. For gas sensing application, as-fabricated SnO₂ microreactors exhibit high and fast responses to nitrogen dioxide (219.5 to NO₂ of 50 ppm) and other gases. The good sensing properties should be indeed ascribed to the specific construction of microreactors, which shows elaborate hierarchical porous structures and large accessible space/surface area favorable for both gas molecule transports and sensing reactions. This present strategy provides us with new insight on the exploring of effective and low-cost gas sensors, and it could further extend to other pollen grains of numerous different morphologies and other types of bioreactors that are abundant in nature.