Mode-filtered light methane gas sensor based on cryptophane A Original Research Article

A mode-filtered light sensor has been developed for methane (CH4) gas determination at ambient conditions. The proposed chemosensor consisted of an annular column which was constructed by inserting an optical fiber coated with a thin silicone cladding of cryptophane A into a fused-silica capillary. When CH4 was introduced to the sensor, selective inclusion of CH4 into the silicone layer would cause a change in the local refractive index of the cladding, resulting in the change of mode-filtered light that emanated from the fiber. Three detection windows were set alongside the capillary to propagate the light to a charge-coupled device (CCD). The changes of mode-filtered light on exposure to various concentrations of CH4 were thus simultaneously monitored. The mode-filtered light intensity decreased with the increase in concentration of CH4. The dynamic concentration range of the sensor for CH4 was 0.0–16.0% v/v with a detection limit of 0.15% v/v. The highest sensitivity was found at the channel furthest away from the excitation light source. The response time (t95%) was about 5 min. The reproducibility was good with a relative standard deviation (RSD) of less than 7% from evaluating six cryptophane A-coated fibers. Oxygen, hydrogen and carbon dioxide showed very little interference on detection but interferences from dichloromethane and carbon tetrachloride were observed. The proposed mode-filtered light sensor has been successfully applied to determine CH4 samples and the accuracy was good. Our work offers a promising approach for CH4 detection.