Metamaterial based optical nanostructures refer to engineered material with properties not readily available in nature, and diversified sensing applications have been investigated. For example, metamaterial absorber is gaining attention for energy efficient Nondispersive Infrared sensor for large scale green-house CO₂ gas monitoring applications. However, miniaturization of the technology remains a major issue. Integration with smart, gas selective material toward the realization of “hybrid metamaterial” absorber is believed to be a viable approach for the system miniaturization. Here, we present a novel hybrid polymer-metamaterial absorber approach for miniaturized and selective optical sensing of CO₂ gas in the 5-8 μm mid IR (Infrared) spectral window for the first time. The new class of sensor offers ppm-level limit of detection at ambient temperature, fast response time (~2 minutes) and large differential change for all-optical monitoring on a small foot print (20μm by 20μm). As proof-of-concept, we report net absorption enhancement of 0.0282%/ppm and wavelength shift of 0.5319 nm/ppm. The gas selective smart material is found to enable dual-mode multiplexed sensing for cross checking and validation of gas concentration on the single platform. The obtained results will pave the way for physical understanding of metamaterial based sensing when integrated with mid-IR detector for on-chip readout and extending the mid-IR functionalities of selective materials for the detection of technologically relevant gases. Meanwhile, the feasibility of using this platform for chemical sensing and biomolecule detection will be highlighted as well.