Microfluidic device concept based on microoscillator dynamics at a liquid–liquid interface

Oscillating microbeams and microplates have been used extensively as sensing components for property detection in fluids. In liquids, their quality factor Q is drastically decreased, thus affecting a microsensor's resolution. To improve the Q-factor, we present a novel concept based on the positive use of surface tension on a mechanical oscillator composed of a microbeam–microplate assembly suspended at a liquid–liquid interface in a microfluidic channel. An analytical model is developed to investigate rotational dynamics of such an assembly. Surface tension effects at the liquid–liquid–solid perimeter line produce responses that are considerably different from those in a single fluid. It is shown that due to surface tension the Q-factor and the response are magnified by orders of magnitude, thus confirming that liquid–liquid interfaces enhance the oscillator's sensitivity. For two liquids the Q  -factor varies as [σ2-σ1]1/2×(μ2+μ1)-1[σ2-σ1]1/2×(μ2+μ1)-1 and for a single liquid as ρ1/2×μ-1ρ1/2×μ-1, (σ,μσ,μ) being surface tension and viscosity, respectively. Microdevice design, actuation and sensing mechanisms, and optimal parameter selection are proposed.