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Resonating Mass Sensors for Detecting Microgram Scale Objects in Fluids


We demonstrate a simple and inexpensive sensor capable of weighing microgram- scale objects in fluid. When objects flow through a glass tube that is vibrating at its resonance frequency, the frequency changes by an amount that is inversely proportional to the object’s buoyant mass. By measuring this frequency change, microgram objects can be weighed in fluid with nanogram-scale resolution. These sensors are easily fabricated, require no labels or tags, and are versatile, making them a valuable instrument for both in situ and laboratory measurements. They are fully automated and can measure any appropriately sized object in a wide range of biological, physical, and chemical applications. Using resonating glass tubes, we demonstrate the mass change detected in zebrafish (D. rerio) embryos as they are exposed to various toxicants, the water uptake and germination of dry seeds as they are put in water, and degradation rates in biomaterials in different fluid media.

Aside from the experimental data from two separate resonator geometries, we also present simulations on other geometries that can be explored for these sensors. We explore the advantages and disadvantages in each geometry and potential sources of measurement error associated with the resonators. The simulations allow us to predict the resolution and the quality factor of the resonator before a prototype is developed.

We took advantage of various rapid prototyping techniques, including 3D printing for developing these sensors. In this process, we discovered that 3D printed parts produce a toxic effect in zebrafish embryos. This observation led to a separate project, in which we assessed the toxicity of printed parts from two main classes of commercial 3D printers, fused deposition modeling and stereolithography. We used zebrafish embryos, a widely used model organism in aquatic toxicology and monitored them for rates of survival, hatching, and developmental abnormalities. We found that parts from both types of printers were measurably toxic, with STL-printed parts significantly more toxic than FDM-printed parts. We also developed a simple post-printing treatment (exposure to ultraviolet light) that largely mitigates the toxicity of the STL-printed parts. Our results call attention to the need for strategies for the safe use and disposal of 3D-printed parts and printer waste materials.

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