  Micro-/nanomechanical mass sensors are capable to quantitatively determine
molecule mass from only first three (two) measured cantilever (bridge) resonant
frequencies. However, in liquid solutions that are relevant to most of the
biological systems, the mass determination is challenging because the Q-factor
due to fluid damping decreases and, as a result, usually just the fundamental
resonant frequencies can be correctly identified. Moreover, for higher modes
the resonance coupling, noise and internal damping have been proven to strongly
affect the measured resonant frequencies and, correspondingly, the accuracy of
the estimated masses. Here, we derive the easy accessible expressions enabling
the quantitative mass(es) determination just from the fundamental resonant
frequencies of the micro/nanomechanical mass sensor under intentionally applied
axial tension, which can be easily created and controlled by the electrostatic
or magnetostatic forces. We also show that typically achievable force
resolution has a negligible impact on the mass determination and the mass
sensitivity.
