Boron Nitride Nanotubes for Optical Fiber Chemical Sensing Applications

Boron nitride nanotubes (BNNTs) are 1-D hollow fibrous nanomaterials. They are thermally stable up to 800 °C in open air and up to 1000 °C in a pure chlorine atmosphere, are electrically insulating, and possess superlative mechanical properties. Since the BNNT assembly is highly porous and easily penetrated by liquids and gases, BNNT thin film coated on optical fiber can be used as a novel sensing medium with enhanced sensitivity and selectivity. In this letter, uniform BNNT films have been successfully coated on optical fibers and tapered optical fibers (TOFs). A BNNT-coated TOF sensor has been developed for various liquids and gases sensing applications. We demonstrated experimentally that the BNNT-coated TOF can be used as a level sensor for liquids, even for those with refractive indices smaller than that of silica such as the organic solvents like acetone, hexane, tetrahydrofuran, ethyl ether, and dimethylformamide. As to gas sensing, HCl was selectively detected with enhanced sensitivity due to its high polarity and good affinity to the OH/NH2 functionalized BNNTs. The BNNT-coated optical fiber sensors can be potentially used at high temperatures and in some harsh environments.