We investigated photonic crystal-based dual-nanoring (DNR) channel drop filters for nanomechanical sensor applications. The backward drop mechanism is explained by a proposed model. A resonant peak at 1553.6 nm with a quality factor better than 3800 is observed at the backward drop port. When this DNR is integrated at the junction between the silicon cantilever and the substrate, the deformation of the silicon cantilever can be detected in terms of the resonant wavelength and resonant wavelength shift. The derived minimum detectable force is 37 nN.