Plasmons in graphene present desirable electronic properties and unique opportunities to enhance light–matter interactions and control light at nanoscale dimensions. The combination of graphene with metal nanostructures is promising for optical science and plasmonic manipulations. We propose a graphene plasmonic system based on a resonant metal antenna for detection and counting of nanoparticles. The performance of the proposed system relies on the intrinsic properties of particles, including the refractive index, which can be used to modulate the transmitted power. Simulations show that, by a small change in the refractive index of the particle, the transmitted output power changes significantly. A local change of ±10% in the refractive index of a 50-nm dielectric particle around the nanopore results in a ∓2.3% variation in the transmitted power corresponding to a sensor sensitivity of 415 nm/RIU. Small particles with a diameter of 20 nm can be detected using this configuration. The placement of a nanopore and nanoparticle in front of the metal antenna can change the spatial near-filed distribution of graphene plasmons and control their propagation wavefronts. Furthermore, the proposed structure with its small footprint can be readily integrated into lab-on-a-chip devices for practical biosensing applications. This plasmonic device is promising for use in single-particle detection and biological applications.