ABSTRACT
Hydrogen (H2) is a source of energy in chemical, transportation, health, and manufacturing industries. But H2, being a light, colorless, and odorless gas, can easily leak out from a source into the atmosphere without being detected. Then, this gas, due to its low density (≈ 0.07), at a high atmospheric concentration, can disbar the supply of free O2 to living organisms, causing asphyxia or other respiratory problems. Also, this gas, with an explosive limit of 4–75% (v/v), is known to be highly inflammable and can crack or explode exposed metals. Further, this gas can ignite even at 0.02 mJ energy, leading to serious hazards and safety issues for living organisms. Apart from this, occasional production of the gas has been reported from the waste tanks of nuclear plants, which could cause nuclear explosion. Moreover, liquid H2 can act as a cryogen to cause freezing of living organisms. Therefore, monitoring or sensing of this gas is crucial for human and environmental safety. Detection of H2 must be highly sensitive, specific, simple, economic, and feasible at a wide range of temperature, pressure, acidity, etc. Several methods for detection of H2 have been reported by researchers around the world, but still it remains a big challenge to develop a quick, specific, and sensitive method for the real-time detection of H2. During the recent past, H2 sensors have dramatically replaced the existing conventional methods, and optical nanosensors are unique among them, mostly because of their sensitivity, specificity, low cost, and reproducibility. Optical sensors may detect H2 directly using Fourier transform infrared spectroscopy or Raman spectroscopy, or they may detect optical changes induced by H2 through surface plasmon resonance, interferometry, or fiber grating analysis. This chapter will focus on different H2 detection methods based on optical sensors.
