Nonlinear topological responses in the vicinity of the exceptional points (EPs) of non-Hermitian systems significantly enhance the eigenmode splitting sensitivity to external perturbations. This study proposes an innovative non-contact EP preparation scheme based on a capillary-based microcavity embedded with one pair of rectangular defects, and EP state can be prepared through controlling asymmetric the backscattering. Compared to conventional EP preparation methods such as nano-scatterer-based or parity-time schemes with rigorous gain and loss balance, our proposed approach circumvents the difficulty in precise positioning of nano-scatterers, thereby enhancing device stability and controllability to facilitate engineering applications of high-performance sensors. The performances of the proposed capillary-based EP sensor for refractive index sensing and nanoparticle detection near the exception point are investigated. In comparison with its diabolic point (DP)-based counterpart with the same target nanoparticle dimension, whispering gallery mode (WGM) microcavity operating around the EP state exhibits 21-fold sensitivity enhancement in nanoparticle detection. And moreover, the proposed capillary microcavity sensor achieves a RI sensitivity up to 5557.509 GHz/RIU for the refractive index range of 1.3474 to 1.3486 based on the interrogation of beat note between the two counterpropagating eigenmodes. This surpasses the detection limits of traditional linear-response sensors and paves new way toward developing EP-based sensors for single-molecule detection of biochemical analytes.