Polymer piezoresistive microcantilever CO sensor and method of making the same. The CO sensor (1) comprises a cantilever (2) extending from a base (3) and having contacts (4) at the top thereof. The cantilever further comprises a coating of Fe(III) porphyrin (5, 10, 15, 20-tetra(4,5-dimethylphenyl)-21H, 23H- porphyrin iron (III) chloride) at the top thereof (5) and a CO disorbent material coating at the bottom thereof (6). The method comprises fabricating a cantilever extending from a base and having contacts at the top thereof; and applying a coating of Fe(III) porphyrin (5, 10, 15, 20-tetra(4,5-dimethylphenyl)-21H, 23H- porphyrin iron (III) chloride at the top of the cantilever and a coating of CO disorbent material at the back of the cantilever. The coated cantilever is allowed to dry at atmospheric conditions. The CO sensor has high sensitivity and selectivity and fast response towards CO in real world conditions. It is simple and easy to fabricate and is compact. It is also of low cost and is suitable for low power applications. It is stable and durable and can be used multiple times. It is fully recoverable after repeated exposures and can be regenerated and reused. It can be used in various CO sensing applications and can also be easily integrated into hand-held devices for many real-world applications.