Pulled microcapillary tube resonators with electrical readout for mass sensing applications

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 (P mu TR) simply supported at two contacts. While a piezo actuator beneath the actuation node excites the P mu TR, the QTF senses the resonance frequency of the P mu TR. The proposed concept was validated by electrical and optical measurements of resonant spectra of P mu TR. Then, different liquid samples including water, ethanol, glycerol, and their binary mixtures were introduced into the P mu TR and the resonance frequency of the P mu TR was measured as a function of liquid density. Density responsivity of -3,088 Hz-g(-1) cm(3) obtained is comparable to those of microfabricated hollow resonators. With a micro droplet generation chip configured in series with the P mu TR, 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 mu m. Overall, typical off-the-shelf parts simply constitute a resonant mass sensing system along with a convenient electrical readout.