Towards Single-Particle Nanomechanical Mass Spectrometry
Mehmet Selim Hanay
California Institute of Technology
Abstract: We will describe our recent efforts to perform mass spectrometry on single molecules and nanoparticles using Nanoelectromechanical Systems (NEMS). Mass spectrometry, i.e. techniques used to identify biomolecules through mass measurements, fulfills an indispensable role in proteomics and environmental research. In the last decade, NEMS devices have begun to offer unprecedented sensitivities for mechanical mass sensing and they are among the candidates for emerging nanoscale tools. Our research demonstrates the proof-of-concept realization of mass spectrometry using NEMS devices. In our first experiments, we transduce the fundamental flexural mode of a nanomechanical beam (at 450 MHz) to detect various proteins and 5-nm gold nanoparticles at the single particle level with 10-kDa resolution. These species are created by Electrospray Ionization and transported to NEMS by hexapolar ion guides in a cryogenic, differentially-pumped setup. These first experiments —while they clearly demonstrate single particle events— do not directly yield information about the mass of the species at the single particle level, as the influence of the particle depends not only on its mass but also its position along the device. Therefore, we employed a statistical approach to process our data and obtain mass information about the samples.
To overcome the position-dependent responsivity of NEMS devices, we developed and implemented multimode methods which can determine the mass of a single particle. Furthermore, we constructed a framework to calculate the confidence levels for mass measurements from the frequency noise statistics of the NEMS modes — an analysis missing from the NEMS literature so far. These methods are utilized in a second experiment where we track the first two mechanical modes of a nanomechanical beam to measure the masses of 10-nm gold nanoparticles one by one. Our work highlights the potentials and challenges for mechanics-based mass spectrometry schemes.
27.09.2011 FENS G029 14:40-16:30