One of the characteristics of the photonic crystals is the confinement of light in a small modal volume with high quality factor. The microdisk geometry is one the photonic crystal structures that confine modes are known as the whispering gallery modes which are located near the marginal volume of the disk. In this paper, we present a combined microdisk system with a single circular array of cubical air-holes near its periphery to form an embedded circular photonic crystal and to provide a better control of the modes. These cubical air-holes are connected with grooves to a depth equal to a fraction of the thickness of the microdisk, designed and engineered for application of a nano-sensor. The finite element simulation results show that the modal volume can be as large as 0.077(λ/n)³ in a region of a central groove. Sensor characteristics are analyzed for various disk geometries, photonic crystal arrays, and dimensions of the connecting slots. Acceptable sensitivities equal to 100 nm/RIU (refractive index unit) are accessible.