In this paper, for the first time, the mass sensitivity of a 3-DoF mode localized electrostatic coupled resonator was characterized under atmospheric pressure. A reversible method was used in which nanoparticles are added on and removed from one resonator of the 3-DOF coupled resonator system. Besides, a comparison of three mass sensitivity characterization methods was carried out: resonance frequency shift, amplitude change and resonance vibration amplitude ratio. The results show that a 3-DOF mode localized coupled resonator has potential to be employed for biosensing applications.