Recent advances in MEMS mass spectrometers

Concept and simulation of a novel dual-layer linear ion trap mass analyzer for micro-electromechanical systems mass spectrometry

This paper proposed a dual-layer linear ion trap mass analyzer (dLIT) based on micro-electromechanical systems (MEMS) technology and stacked-layer structure for the development of MEMS mass spectrometry. Its basic performance and potential capabilities were explored by ion trajectory simulations. The theoretical formulas were modified by implementing multipole expansion. The simulation results were confirmed to be highly consistent with theoretical calculations in multiple aspects, including stability diagram, secular frequencies, and mass linearity, with only a deviation of 1-2%. In the boundary ejection mode, close to 100% ejection was achieved in a single dimension by applying extra quadrupole DC voltage. Preliminary simulation results showed that dLIT can achieve a peak width of ∼2 mass units (full width at half maximum, FWHM) for m/z 60 ions even at pressures as high as 50 Pa. Furthermore, the application of AC frequency scanning mode in dLIT was also evaluated, and preliminary simulation results yield a peak width of 0.3-0.4 mass units (FWHM). The dLIT offered several advantages, including high-precision fabrication at the sub-millimeter scale, excellent high-pressure performance, and a clear physical model. It preliminarily proved to be an ideal mass analyzer for MEMS mass spectrometry.

A Piezoelectrically Excited ZnO Nanowire Mass Sensor with Closed-Loop Detection at Room Temperature

One-dimensional nanobeam mass sensors offer an unprecedented ability to measure tiny masses or even the mass of individual molecules or atoms, enabling many interesting applications in the fields of mass spectrometry and atomic physics. However, current nano-beam mass sensors suffer from poor real-time test performance and high environment requirements. This paper proposes a piezoelectrically excited ZnO nanowire (NW) mass sensor with closed-loop detection at room temperature to break this limitation. It is detected that the designed piezo-excited ZnO NW could operate at room temperature with a resonant frequency of 417.35 MHz, a quality factor of 3010, a mass sensitivity of -8.1 Hz/zg, and a resolution of 192 zg. The multi-field coupling dynamic model of ZnO NW mass sensor under piezoelectric excitation was established and solved. The nonlinear amplitude-frequency characteristic formula, frequency formula, modal function, sensitivity curve, and linear operating interval were obtained. The ZnO NW mass sensor was fabricated by a top-down method and its response to ethanol gas molecules was tested at room temperature. Experiments show that the sensor has high sensitivity, good closed-loop tracking performance, and high linearity, which provides great potential for the detection of biochemical reaction process of biological particles based on mechanics.