Abstract
This paper reports a microfabrication-free approach to make hollow channel mass sensors by pulling a glass capillary and suspending it on top of a machined jig. A part of the pulled section makes simple contact with an actuation node and a quartz tuning fork (QTF) which acts as a sensing node. The two nodes define a pulled micro capillary tube resonator (PμTR) simply supported at two contacts. While a piezo actuator beneath the actuation node excites the PμTR, the QTF senses the resonance frequency of the PμTR. The proposed concept was validated by electrical and optical measurements of resonant spectra of PμTR. Then, different liquid samples including water, ethanol, glycerol, and their binary mixtures were introduced into the PμTR and the resonance frequency of the PμTR was measured as a function of liquid density. Density responsivity of −3,088 Hz-g−1 cm3 obtained is comparable to those of microfabricated hollow resonators. With a micro droplet generation chip configured in series with the PμTR, size distribution of oil droplets suspended in water was successfully measured with the radius resolution of 31 nm at the average droplet radius, 28.47 μm. Overall, typical off-the-shelf parts simply constitute a resonant mass sensing system along with a convenient electrical readout.
Highlights
This paper reports a microfabrication-free approach to make hollow channel mass sensors by pulling a glass capillary and suspending it on top of a machined jig
Nanoelectromechanical systems (NEMS) resonators have achieved zeptogram-scale mass resolution almost a decade ago[6] and bottom-up synthesized nanomaterials based resonators have enabled single atom[7] and proton[8] resolution
Exceptional resolutions achieved with NEMS and nanomaterials based resonators are in general limited to ideal conditions such as high vacuum levels and cryogenic temperatures
Summary
This paper reports a microfabrication-free approach to make hollow channel mass sensors by pulling a glass capillary and suspending it on top of a machined jig. Exceptional resolutions achieved with NEMS and nanomaterials based resonators are in general limited to ideal conditions such as high vacuum levels and cryogenic temperatures Such experimental environments are far from being compatible to portable field applications and minuscule matters suspended in liquid, not to mention that the maintenance of such operating conditions requires intensive time, cost and labor. The embedded channel localizes liquid samples and makes suspended particles guided towards the mass sensing region on demand. This is a unique advantage of hollow resonators over solid ones that are fully exposed to liquid sample and passively observe stochastic landing of suspended particles. (c) A pulled micro capillary tube resonator (PμTR) of which one nodal point is defined by a physical contact to one of two prongs of a QTF. The scale bar is 1 mm. (c) A pulled micro capillary tube resonator (PμTR) of which one nodal point is defined by a physical contact to one of two prongs of a QTF. (d) Assembly process of PμTR-QTF system (not to scale). (e) Photographs of an assembled PμTR-QTF sensing platform ready for testing
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