Highly Sensitive Measurement of Liquid Density in Air Using Suspended Microcapillary Resonators

Abstract

We report the use of commercially available glass microcapillaries as micromechanical resonators for real-time monitoring of the mass density of a liquid that flows through the capillary. The vibration of a suspended region of the microcapillary is optically detected by measuring the forward scattering of a laser beam. The resonance frequency of the liquid filled microcapillary is measured for liquid binary mixtures of ethanol in water, glycerol in water and Triton in ethanol. The method achieves a detection limit in an air environment of 50 µg/mL that is only five times higher than that obtained with state-of-the-art suspended microchannel resonators encapsulated in vacuum. The method opens the door to novel advances for miniaturized total analysis systems based on microcapillaries with the add-on of mechanical transduction for sensing the rheological properties of the analyzed fluids without the need for vacuum encapsulation of the resonators.

Precision density and viscosity measurement using two cantilevers with different widths

“…The minimum detectable viscosity and density change can be calculated from the noise floor of the frequency measurement (0.65 Hz) and the frequency difference between calibration liquids. Based on the signal-to-noise ratio, the minimum detectable differences in the viscosity and the density are 1 Pa.s and 0.18 kg/m 3 respectively which is comparable with the recent work which reports 0.05 kg/m 3 minimum detectable density using microcapillary resonators [17]. Table 2 Viscosity results obtained from reference measurements and the proposed method.…”

“…A general approach to separate viscosity and density effects experimentally is to relate quality factor changes with viscosity and resonant peak shifts with density [6][7][8][9]. This approach is also used with other types of MEMS structures like Suspended microchannel resonators (SMR) [11,12] and piezoelectric MEMS resonators [13][14][15][16] and suspended microcapillary resonators [17]. With this approach in order to attain high sensitivity in a broad dynamic range, frequency sweeps with high frequency resolution is necessary.…”

Pulled microcapillary tube resonators with electrical readout for mass sensing applications

“…Interestingly, a commercially available microcapillary suspended over a pre-defined trench seems very promising since it is potentially available to anyone. Suspended microcapillary resonators with optical detection were employed for liquid density measurements 25 and differentiation of X- and Y- chromosome bearing sperm cells 26 . Despite the absence of commercially available nanoscale capillary tubes, suspended nanocapillary resonators 27 have been simply fabricated by using polymer nanofibers deposited over lithographically pre-defined trenches as sacrificial templates and used with an optical interferometry.…”

Real-Time Particle Spectrometry in Liquid Environment Using Microfluidic-Nanomechanical Resonators

“…Moreover, the fabrication process of these sensors remains complex, costly and time consuming. In response to this concept, doubly-clamped fused silica capillary micro-tubes were proposed in previous works [8] as a simpler and inexpensive alternative for HNMRs, but, as a counterpart, they present a lower buoyant mass resolution than silicon hollow cantilevers, of about 100 pg [9].…”