Sub-ppm NO2 gas sensing in CdTe quantum dots functionalized hollow-core anti-resonant fiber

Recently emerged hollow-core fiber provides an excellent platform for various studies due to its remarkable features, such as broadband transmissions, enhanced light-matter overlapping, ultra-low nonlinearity, low latency and dispersion. At the same time, it is generally known that nitrogen dioxide (NO2) is deemed a common air pollutant. Detecting its concentration is essential, covering environmental monitoring, industrial manufacturing, and human safety issues. Accurate detection of NO2 in gaseous state, however, has been a long-existing challenge due to the requirements for high sensitivity, compatible equipment, short sampling duration, etc. Here, a novel approach is reported for measuring NO2 gas by functionalizing a hollow-core anti-resonant fiber (HC-ARF) with CdTe-deposited quantum dots (QDs). The mechanism is based on fluorescence quenching of glutathione-capped CdTe QDs, triggered by NO2 gas. The hollow-core fiber works as a micro-reactor that enhances gas/light interactions. Consequently, the sensitivity can be effectively increased for detecting sub-ppm concentration (∼0.1 ppm) NO2 gas, with high efficiency, small sample volume, and short sampling durations of only a few minutes, much faster than that in many non-fiber-based systems. Such a rapid detection of low-concentration NO2 is applicable in most scenarios. These results provide a reliable, compatible, and promising solution for chemical and biological sensing of gas or liquid-phased substances in hollow-core fibers.