Measuring Tiny Masses Acoustically

How do you measure the mass of something really, really tiny? Like fish-embryo tiny. There aren’t many scales with the sensitivity and the resolution to make meaningful measurements in the nanogram range, so you’ve got to turn to other methods, like measuring changes in the resonant frequency of a glass tube. And that turns out to be cheap and easy for the home gamer to reproduce.

In a recent scholarly paper, [William Grover] et al from the University of California Riverside outline the surprisingly simple and clever method of weighing zebrafish embryos, an important model organism used in all sorts of developmental biology and environmental research. [Grover]’s method is a scaled-up version of a suspended microchannel resonator (SMR), a microelectromechanical device that can measure the mass of single cells or even weigh a virus particle. Rather than etch the resonator out of silicon, a U-shaped glass tube is vibrated by a piezoelectric speaker and kept at its resonant frequency by feedback from a cheap photointerrupter. When an embryo is pumped into the tube, the slight change in mass alters the resonant frequency of the system, which is easily detected by the photointerrupter. The technique can even be leveraged to measure volume and density of the embryos, and all for about $12 in parts.

In the lab, [Grover]’s team uses a data acquisition card and LabVIEW to run the resonant loop, but there’s no reason a DIY version of this couldn’t use an Arduino. In fact, tipster [Douglas Miller] expects someone out there will try this, and would appreciate hearing the details. You can ping him on his page.

11 thoughts on “Measuring Tiny Masses Acoustically

  1. There was an article in Scientific American in 1990’s about using an analog meter as scale. Meter was on its side and pointer was extended (IIRC). Sample was placed at its end, then current (or voltage) was adjusted to make it horizontal, this translated directly to measured mass. It was very simple yet precise instrument…

  2. My immediate thought on seeing this is it would make a good continuous fluid density measuring device. As you have a fixed volume and it’s easy enough to measure pressure and temperature.

    1. The mass flow messes with the measurement – kinda like trying to measure something with a balance beam scale when the cups are swinging around.

      It’s possible to account for the error, but you have to know how fast the fluid is moving.

  3. Pretty resourceful, those biology hackers.

    Long time ago (I was beginning my Phisics studies, so 1975-76) I got to know a biologist working on his PhD. He wanted to research bees and their harvesting “economy”, trying to correlate the distance to the nectar source to the amount they took with them.

    Knowing that they don’t fly in the dark, he trained them to enter his lab’s window through a narrow, dark passage, after which the nectar “treat” was to be found.

    This passage’s floor of was a thin metallized plastic film which gave in a bit under the bee’s weight and was one of the plates of a capacitor, the other below it: the increase in capacitance was a function of the bee’s weight, and the amount of nectar could be inferred by the difference in weight on the bee’s way in and out.

    The metallized film was sourced at… a nearby capacitor factory, somehow closing this magic circle.

    As a young student I was *very* impressed.

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