Recently,microfiber-optic sensors with high sensitivity,fast response times,and a compact size have become an area of interest that integrates fiber optics and nanotechnology.Distinct advantages of optical microfiber,such as large accessible evanescent fields and convenient configurability,provide attractive benefits for micro-and nano-scale optical sensing.Here,we review the basic principles of microfiber-optic sensors based on a broad range of microstructures,nanostructures,and functional materials.We also introduce the recent progress and state-of-the-art in this field and discuss the limitations and opportunities for future development.