Mass measurements on beads, cells and cellular compartments with FluidFM

Digital FluidFM Conference 2021

Mass measurements on beads, cells and cellular compartments with FluidFM

Proposed by Hans Gunstheimer

In this presentation we will discuss mass measurements by FluidFM® Micropipettes, their accuracy and limits illustrated with examples from biology and material science.

Mass as a fundamental property gives us valuable information about the condition of a measurement object. Taking a single biological cell for example, the dysregulation of its mass and its mass development can be related to many diseases (1). To relate the mass of the cell to its condition it is favorable to combine it with other techniques. Correlative mass measurements and optical microscopy is one obvious possibility, but also the combination with mechanical properties like adhesion or elasticity are of interest. It has been shown by this method that the cell mass fluctuates and increases over time for healthy cells (2). In contrast, virus-infected cells stop growing and energy depletion or blockage of water channels reduces fluctuations in the cell mass. In material science swelling and dissolving of single particles or thin films can be observed through the change in mass. Measuring various beads of the same kind gives us information about the mass distribution within one batch.

Using a conventional balance to gain insights into the mass of tiny objects is not possible as their lower limit of calibration is at 1 milligram (3). By measuring the inertial mass of these objects with a cantilever pushes down this limit. This kind of measurement determines the mass by the drop of resonance frequency when an additional mass is attached to the cantilever.

The combination of FluidFM® Micropipettes and the DriveAFM® with photothermal excitation enables reversible binding of single objects to a cantilever and their mass measurements in liquid at the sub-nanogram scale. When the cantilever is directly actuated by photothermal excitation the frequency spectrum can be obtained with low noise and in combination with a phase-locked loop the changes in resonance frequency can be tracked with millisecond time resolution. Using FluidFM® Micropipettes we could easily attach an object to the opening of the cantilever by applying negative pressure and release it with positive pressure.

To determine the accuracy of the presented picobalance, particles of different sizes and density were attached to a FluidFM® Micropipette. The measured mass related well to the expected mass with a narrower distribution than that derived the manufacturer specifications.

The frequency drop not only depends on the mass, but also on the position of the mass on the cantilever. This is given when working with FluidFM® probes. Alternatively, this can be determined optically or by exciting the cantilever at its higher flexural modes (4). The derived position by higher flexural mode excitation was compared to and fitted close to the position of opening in the FluidFM® probe.

From the obtained results we conclude that the presented technology can be reliably used to measure the mass of cells and changes therein.

(1) Lloyd, A. C. Cell 154, 1194 (2013)
(2) Martinez-Martin D. et al. D. Nature, 550, 500 (2017)
(3) OIML r111-1:2004 (2004)
(4) Dohn S. et al. Rev. Sci. Instr. 78, 103303 (2007)

Nanosurf AG, Hans Gunstheimer

Hans Gunstheimer

R&D Engineer, Nanosurf AG, Switzerland

Hans is a mechanical engineer with a thirst for knowledge in micro- and nanotechnology, who gained his M.Sc. degree from TU Ilmenau. For his master thesis he joined the development and applications team of Nanosurf AG in Switzerland for the PicoBalance project where he measured the mass of beads and cells using FluidFM® Micropipettes. Currently, he is focusing on the probe production for AFM-SECM.

Practical Info

Dec 01, 2021 11:15 AM (Europe/Zurich)
20 minutes