Single nanoparticle sensing with nanoelectromechanical resonators operating at nonlinear regime

Machines working at the nanoscale dimensions o er an important technological opportunity for healthcare and biomedical screening. State-of-the-art nanomachines are usually operated at small displacements, since engineering tools for their control at large vibration amplitudes have so far been absent. Nanoelectromechanical Systems (NEMS) have emerged as a promising technology for performing the mass spectrometry of large biomolecules and nanoparticles. Nanoparticles constitute an important family in the nanotechnology toolbox, because they indicate potential pollutions early on, or can be designed to act as drug carriers for cancer therapy. As nanoscale objects land on NEMS sensor one by one, they induce resolvable shifts in the resonance frequency of the sensor proportional to their weight. The operational regime of NEMS sensors is often limited by the onset-of-nonlinearity, beyond which the highly sensitive schemes based on frequency tracking by phase-locked loops cannot be readily used. Here, we develop a measurement architecture to operate at the nonlinear regime and measure frequency shifts induced by analytes in a rapid and sensitive manner. We used this architecture to individually characterize the mass of gold nanoparticles and veri ed the results by performing independent measurements of the same nanoparticles based on linear mass sensing. Once the feasibility of the technique is established, we have obtained the mass spectrum of a 20 nm gold nanoparticle sample by individually recording about ve hundred single particle events using two modes working sequentially in the nonlinear regime. The technique obtained here can be used for thin nanomechanical structures which possess a limited dynamic range.