Detection of gases such as CO₂, methane, and hydrogen is critical for environmental monitoring, industrial safety, and controlling greenhouse gas emissions yet existing gas sensing technologies often face challenges related to inadequate sensitivity, slow response times, high costs, and limited long-term stability. Traditional sensors may be bulky, expensive, or rely on complex nanofabrication techniques, making them impractical for widespread or distributed sensing applications. Fiber optic sensors offer advantages such as immunity to electromagnetic interference and potential for remote and distributed sensing. However, conventional designs may suffer from insufficient sensitivity or degradation over time due to polymer aging. Additionally, many sensors require high operating temperatures or struggle to detect chemically stable gases at room temperature, further limiting their practicality. Consequently, there is a pressing need for cost-effective, highly sensitive, and stable gas sensing solutions that operate efficiently at room temperature and can be easily scaled for use in large-area monitoring and distributed sensor networks.

NETL has overcome these obstacles with its economical, highly sensitive plasmonic CO₂ sensor. Indium oxide (ITO) pNPs are incorporated into a CO₂ sorbent polymer matrix (PIM-1) on a fiber optic (FO) platform. The sensor is easily fabricated by coating a cladding-exposed section of optical fiber with an ITO pNPs-PIM-1 composite. Connecting one end of the optical fiber to a light source and the other to a spectrophotometer allows the optical response of the ITO pNPs-PIM-1 FO sensor to be evaluated via optical transmission spectroscopy. In the absence of CO₂, the sensor exhibits a distinct absorption band at 1245 nm associated with the optical response (i.e., LSPR) of the ITO pNPs. When the sensor is exposed to CO₂, the PIM-1 matrix adsorbs CO₂. This alters the environment of the embedded ITO pNPs, changing their optical response and attenuating the 1245 nm absorbance band. This attenuation correlates linearly with the concentration of CO₂, is reversible, and occurs rapidly with response and recovery times of tens of seconds. Such sensitivity to CO₂ is long-lasting (> 40 weeks), indicating its usefulness for long-term CO₂ monitoring.  

Varying the pNPs content in the polymer matrix can be used to tune the sensor to specific operational wavelengths. This is a critical feature for FO-based sensing, where using commercially standard telecom wavelengths can dramatically reduce optical interrogator costs. The sensor can also be tuned to detect other gases such as methane and hydrogen by selecting an appropriate gas-specific polymer sorbent.