A brand new design of slot-waveguide is proposed using a subwavelength hollow-core fiber, which enables light to be confined in an extremely small hollow-core with long interaction length. The slot-waveguide fiber (SWF) can be used in various applications such as modulators, directional couplers and multimode interference devices, and it has specific advantages in ultra-low volume optofluidic sensing compared with other waveguide structures. The guiding properties and optimization of the design to maximize its sensitive will be discussed.