White PaperTest & Measurement

Optomechanical Mass Sensing

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Conventional mass spectrometers classify analytes by measuring their mass-to-charge ratio and can resolve single atoms. However, their low dynamic range limits weighing heavier analytes such as colloidal and aerosol particles larger than only a few atoms. Dissociation methods are often used to fragment such particles, changing their native properties and making the reconstruction of the mass spectrum a challenging work.

By contrast, optomechanical sensors measure mass by monitoring the optical modulation transduced by the dynamics of a mechanical system such as a micro-resonator. They offer novel mass sensing schemes with a wider dynamic range and pico- to attogram sensitivity. Further, they enable in situ analysis thanks to their non-destructive nature. An optomechanical sensor’s design can take many forms depending on the environment it operates in and the nature of the particles it probes. To illustrate possible applications, we look at three scenarios:

  • Optical balance for single aerosol particles isolated under atmospheric conditions.
  • Nanomechanical mass spectrometry (NMS) for deposited nanoparticles.
  • Transparent microcapillary resonators (TMRs) for colloids.

In each case, a Zurich Instruments lock-in amplifier provides the signal to drive the mechanical system and extracts the resulting optical modulation separating it from the background.

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