A nanoelectromechanical (NEMS) resonant mass sensor is a suspended cantilever, only a few hundred nanometers across, that is driven to vibrate at its own natural resonant frequency f₀. That frequency depends only on the beam's stiffness k and its total mass m: f₀ = (1/2π)·√(k/m). When a single molecule or virus particle lands on the beam, the total vibrating mass increases by a tiny amount Δm — and because a heavier oscillator always rings at a lower pitch (the same reason a bigger tuning fork sounds deeper), f₀ drops by a measurable Δf. Tracking that shift in real time is the actual readout mechanism used by real NEMS sensors, some of which are sensitive enough to detect the mass of a single proton.
f₀ = (1/2π)·√(k/m)
Δf/f₀ ≈ −Δm/(2m) (for Δm ≪ m)
- Particle mass — heavier simulated particles (e.g. larger virus particles) produce a bigger, more obvious frequency drop per landing event.
- Landing rate — how often a new particle arrives at the cantilever tip during detection.
- Start detection — begins driving the cantilever at resonance and streaming particles toward it; the live chart plots f₀(t) as it steps down with every landing.
Real-world relevance: this is the working principle behind the most sensitive class of mass sensors ever built — used in labs to detect and weigh individual viruses, proteins and even single atoms by watching exactly this kind of resonant-frequency staircase.