Measurement of density and chemical concentration using a microfluidic chip

Abstract

A new microfluidic product for measuring fluid density, specific gravity and chemical concentration has been developed. At the core of this lab-on-a-chip sensor is a vacuum-sealed resonating silicon microtube. Measurements can be made with under a microliter of sample fluid, which is over 1000x less than is conventionally required. Since the product is MEMS-based the overall system size is a fraction of conventional density meters and it weighs much less than the traditional desk-top, temperature controlled, density meters. The syringe or pipette loaded system includes a dynamic temperature control system that operates between 0 degree C and 90 degree C with an accuracy of less than 0.01 degree C. Density measurement accuracies of 4 to 5 digits have been observed with aqueous solutions. Measurement examples and applications will be discussed.

Nonmonotonic Energy Dissipation in Microfluidic Resonators

“…Such devices enable mass measurements of nanoparticles, single bacterial cells, and submonolayers of adsorbed proteins with femtogram sensitivity in liquid [9]. Applications also include ultralow volume universal detection for liquid chromatography [10], the measurement of fluid density [11][12][13], and the measurement of mass flow [14].A key outstanding question is how energy dissipation, and hence sensitivity, scales with the size of the resonator and the density and viscosity of the fluid. We investigate the effect of the fluid only; variations in the intrinsic quality factor with size have been investigated elsewhere [15].…”

“…Such devices enable mass measurements of nanoparticles, single bacterial cells, and submonolayers of adsorbed proteins with femtogram sensitivity in liquid [9]. Applications also include ultralow volume universal detection for liquid chromatography [10], the measurement of fluid density [11][12][13], and the measurement of mass flow [14].…”

Embedded MEMS-based concentration sensor for fuel cell and biofuel applications

“…The resonant microtubes used in this paper employ a MEMS fabrication process, which uses a combination of plasma and wet etching, photolithography, along with wafer bonding to form the microfluidic chips [8,9]. Fig.…”

“…This paper presents a MicroElectroMechanical Systems (MEMS) sensing chip that is being developed for the methanol concentration application. This device has previously been used to measure fluid density and chemical concentration [8,9]. As the mass of the total tube/liquid system increases the vibrational frequency decreases.…”

Quality Factor

“…This concept has been used for years in macroscopic U-tube density meters. More recently, micro and nanomechanical U-tube resonators, also called suspended microchannel resonators, have been successfully used for weighing of biomolecules [12] and nanoparticles [13], and for density [11,14,15] and viscosity [16] measurements. The viscosity detection is non-trivial because the quality factor has been shown to be a nonmonotonic function of the liquids viscosity [17,18].…”