The technology and applications of optical fibers have progressed very rapidly in recent years. Fiber-optic sensors have been commercially successful and well established in various industries from biomedical to defense. They exhibit many advantages over their electrical counterparts, including higher responsivity, higher detection bandwidth, higher temperature performance, better immunity to electromagnetic interference, all-dielectric composition, greater environmental ruggedness and distributed sensing capability. However, the physical dimensions and the minimum bend radius of the optical fiber sets a lower limit on the final package size. In applications where the working space is stringent or where physical intrusion must be minimized, it becomes highly desirable to develop ultra-compact sensors that can maintain the level of performance despite the miniaturization. The recent emergence of optical microfibers has opened up a new era of technological innovations. Microfibers have the potential to solve the problem with its range of enabling properties, including large evanescent field, strong optical confinement, bend insensitivity, low stiffness and high configurability. This thesis focuses on the innovative development of relatively unexplored areas of microfiber-based sensing as well as the envisioning of performance-enhancing techniques that can shape the on-going development of such sensors. In particular, extensive advancement was made in light of the simple demonstration of a novel current sensor with potentially gigahertz detection bandwidth. This includes the development of the resonator design to achieve higher compactness, and the first reported fabrication of the spun optical microfiber to counter the effects of linear birefringence. Well established and successfully proven sensing configurations such as the flexural disc and air-backed mandrel were adopted to create miniaturized microfiber-based accelerometers and microphones, with potential responsivity enhancements of at least one order of magnitude.