Diamond Molecular Balance: Ultra-Wide Range Nanomechanical Mass Spectrometry from MDa to TDa

Abstract

The significance of mass spectrometry lies in its unparalleled ability to accurately identify and quantify molecules in complex samples, providing invaluable insights into molecular structures and interactions. Here, we leverage diamond nanostructures as highly sensitive mass sensors by utilizing a self-excitation mechanism under an electron beam in a conventional scanning electron microscope (SEM). The diamond molecular balance (DMB) exhibits a practical mass resolution of 4.07 MDa, based on its notable mechanical quality factor and frequency stability, along with a broad dynamic range from MDa to TDa. This positions the DMB at the forefront of nanoelectromechanical system (NEMS)-based mass spectrometry operating at room temperature. Notably, the DMB demonstrated its ability to measure the mass of a single bacteriophage T4 by precisely locating the analyte on the device. These findings demonstrate the capability and potential of the DMB as a revolutionary tool for mass spectrometry at room temperature.

Keywords: Bacteriophage T4; Diamond; Mass Spectrometry; Multiplexing4; Nanoelectromechanical Systems.

1

Diamond molecular balances (DMBs). (a) Illustration of DMBs with an incident electron beam. The resonant frequency of the DMB is detuned by the mass of the adsorbed analytes. (inset) A scanning electron micrograph of a bacteriophage T4 virion on top of a DMB (scale bar 300 nm). (b) A SEM image of DMBs (scale bar 2 μm). (c) A TEM image of a DMB (scale bar 5 nm), and (inset) its selected area electron diffraction pattern. The crystallinity of the nanostructure remains well preserved after fabrication processes (scale bar 4 nm^–1). The white arrow indicates the (100) face of the diamond crystal structure.

2

Self-oscillation of DMB and fast Fourier transform analysis. (a) Time-dependent secondary electron intensity resulting from the self-oscillation of the DMB. Secondary electron intensity is periodically modulated by the mechanical motion of the self-oscillating DMB, and the time-dependent intensity signal is well traced by a sinusoidal function. (b) Fast Fourier transform (FFT) result. From the Lorentzian curve fitting, a quality factor of 236,000 was extracted. (inset) Finite element simulation of a resonant mechanical mode of the DMB. The obtained resonance frequency closely matches the finite element calculation result of 7.88 MHz. (c) Frequency stability of the DMB under different time constant conditions. The dashed line indicates the thermal noise limit.

3

Mass detection range of DMB and a theoretical modeling. (a) (upper) Molecular weights of various viruses and . (bottom) Normalized frequency detunings as a function of normalized weights. The measured frequency detunings from six different DMBs with calibrated mass loading in the range of MDa to TDa (pentagon, inverted triangle, triangle, circle, and diamond; for the leftward triangle see Supporting Figure 4) were traced by numerically obtained results based on the theoretical model (solid line, see Supporting Information 5: Electromechanical modeling of the DMB for details). (inset) Frequency shifted responses with the mass loadings of 4.2 MDa and 1.5 TDa. (b) Time-dependent displacement of DMB. (c) Time-dependent charge state of DMB.

4

Mass measurement on a single bacteriophage T4. (a) Detuned frequency response of a DMB before (yellow) and after (purple) loading a single bacteriophage T4. (b) Corrections on frequency detunings as a function of varying positions along the moving direction, the distance from the axis perpendicular to the moving direction, and masses of analytes on the plateau of the DMB. The dashed lines on the plot represent equal values of correction on the frequency detuning. (c) Scanning electron micrograph image (top view) of a single bacteriophage T4 on top of the DMB (scale bar 300 nm). (d) Transmission electron micrograph image of a bacteriophage T4, revealing detailed body structure including tail fibers (scale bar 100 nm).

5

Time-division multiplexed measurement on an array of DMBs. (a) Scanning electron micrograph image of the DMBs (scale bar 1 μm). Locations where the electron beams were directed are indicated by dotted circles. (b) Time-dependent response of DMBs. Portions of the real-time data, sequentially obtained from different DMBs (i–vi), are used for FFT analysis. (c) FFT results obtained from the DMBs (i–vi).