Design strategies for microstructured-optical-fiber (MOF-) based surface-plasmon-resonance (SPR) sensors are presented. In such sensors, plasmons on the inner surface of the large metallized channels containing analyte can be excited by a fundamental mode of a single-mode microstructured fiber. Phase matching between a plasmon and a core mode can be enforced by introducing air-filled microstructures into the fiber core. Particularly, in its simplest implementation, the effective refractive index of a fundamental mode can be lowered to match that of a plasmon by introducing a small central hole into the fiber core. Resolution of the MOF-based sensors is demonstrated to be as low as $3\times {10}^{-5}\mathrm{RIU}$ , where RIU means refractive index unit. The ability to integrate large-size microfluidic channels for efficient analyte flow together with a single-mode waveguide of designable modal refractive index is attractive for the development of integrated highly sensitive MOF-SPR sensors operating at any designable wavelength.