Clinicians and medical researchers count and measure microparticles to identify pathogens, spot cancer cells, and monitor how effective various therapies are at the cellular level. Particle counters that measure the size of objects normally use a beam of light and light sensors to identify objects, but researchers at North Carolina State University developed a brand new method that uses changes in heat to identify particle size.
The device they built consists of a narrow plastic tube sandwiched between a layer of silicon nitride membrane and a polymer. An electrical wire is positioned right next to the plastic tube and is used to generate heat and measure its changing electrical resistance. When a particle passes by the wire it changes the temperature near the wire and in turn the the wire’s electrical resistance. Measuring this resistance provides an excellent indicator of the thermal conductivity of the particle next to the wire, which can be used to interpolate the actual size of the object. The team was able to measure particles between 90 and 200 μm in diameter and believes the same technique can be optimized to get down to 10 μm, which will allow the measurement of individual cells.
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