Neutral mass spectrometry of virus capsids above 100 megadaltons with nanomechanical resonators.

Measurement of the mass of particles in the mega- to gigadalton range is challenging with conventional mass spectrometry. Although this mass range appears optimal for nanomechanical resonators, nanomechanical mass spectrometers often suffer from prohibitive sample loss, extended analysis time, or inadequate resolution. We report on a system architecture combining nebulization of the analytes from solution, their efficient transfer and focusing without relying on electromagnetic fields, and the mass measurements of individual particles using nanomechanical resonator arrays. This system determined the mass distribution of ~30-megadalton polystyrene nanoparticles with high detection efficiency and effectively performed molecular mass measurements of empty or DNA-filled bacteriophage T5 capsids with masses up to 105 megadaltons using less than 1 picomole of sample and with an instrument resolution above 100.

Single-particle mass spectrometry with arrays of frequency-addressed nanomechanical resonators.

One of the main challenges to overcome to perform nanomechanical mass spectrometry analysis in a practical time frame stems from the size mismatch between the analyte beam and the small nanomechanical detector area. We report here the demonstration of mass spectrometry with arrays of 20 multiplexed nanomechanical resonators; each resonator is designed with a distinct resonance frequency which becomes its individual address. Mass spectra of metallic aggregates in the MDa range are acquired with more than one order of magnitude improvement in analysis time compared to individual resonators. A 20 NEMS array is probed in 150 ms with the same mass limit of detection as a single resonator. Spectra acquired with a conventional time-of-flight mass spectrometer in the same system show excellent agreement. We also demonstrate how mass spectrometry imaging at the single-particle level becomes possible by mapping a 4-cm-particle beam in the MDa range and above.

Quantum fluctuations in percolating superconductors: an evolution with effective dimensionality.

We investigate percolating films of superconducting nanoparticles and observe an evolution from superconducting to metallic to insulating states as the surface coverage of the nanoparticles is decreased. We demonstrate that this evolution is correlated with a reduction in the effective/dominant dimensionality of the system, from 2D to 1D to 0D, and that the physics in each regime is dominated by vortices, phase slips and tunnelling respectively. Finally we construct phase diagrams that map the various observed states as a function of surface coverage (or, equivalently, normal state resistance), temperature and measurement current.

Neuromorphic behavior in percolating nanoparticle films.

We show that the complex connectivity of percolating networks of nanoparticles provides a natural solid-state system in which bottom-up assembly provides a route to realization of neuromorphic behavior. Below the percolation threshold the networks comprise groups of particles separated by tunnel gaps; an applied voltage causes atomic scale wires to form in the gaps, and we show that the avalanche of switching events that occurs is similar to potentiation in biological neural systems. We characterize the level of potentiation in the percolating system as a function of the surface coverage of nanoparticles and other experimentally relevant variables, and compare our results with those from biological systems. The complex percolating structure and the electric field driven switching mechanism provide several potential advantages in comparison to previously reported solid-state neuromorphic systems.

Quantized conductance and switching in percolating nanoparticle films.

We demonstrate switching behavior and quantized conductance at room temperature in percolating films of nanoparticles. Our experiments and complementary simulations show that switching and quantization result from the formation of atomic-scale wires in the gaps between particles. These effects occur only when tunnel gaps are present in the film, close to the percolation threshold.