Here we apply nanomechanical resonators to the study of oscillatory fluid dynamics. A high-resonance-frequency nanomechanical resonator generates a rapidly oscillating flow in a surrounding gaseous environment; the nature of the flow is studied through the flow-resonator interaction. Over the broad frequency and pressure range explored, we observe signs of a transition from Newtonian to non-Newtonian flow at $\omega \tau \approx 1$, where $\tau$ is a properly defined fluid relaxation time. The obtained experimental data appear to be in close quantitative agreement with a theory that predicts a purely elastic fluid response as $\omega \tau \to \infty$.

Significance: For the past 50 y, antibiotics have cured common bacterial infections quickly and effectively. Many strains of bacteria, however, are gaining resistance to common antibiotics. The solution to this problem includes a more judicious use of antibiotic therapies, directed by rapid point-of-care antibiotic susceptibility tests. The focus here is a simple all-electrical sensing approach implemented in a microfluidic device that measures the growth of a tiny bacteria sample in antibiotics. This approach has the potential to rapidly provide antibiotic susceptibility of bacteria along with minimum inhibitory concentrations and inform of the mechanisms of action of antibiotics—all without resorting to high-resolution microscopy.

Nanomechanical motion of bacteria adhered to a chemically functionalized silicon surface is studied by means of a microcantilever. A non-specific binding agent is used to attach Escherichia coli (E. coli) to the surface of a silicon microcantilever. The microcantilever is kept in a liquid medium, and its nanomechanical fluctuations are monitored using an optical displacement transducer. The motion of the bacteria couples efficiently to the microcantilever well below its resonance frequency, causing a measurable increase in the microcantilever fluctuations. In the time domain, the fluctuations exhibit large-amplitude low-frequency oscillations. In corresponding frequency-domain measurements, it is observed that the mechanical energy is focused at low frequencies with a 1/f^α-type power law. A basic physical model is used for explaining the observed spectral distribution of the mechanical energy. These results lay the groundwork for understanding the motion of microorganisms adhered to surfaces and for developing micromechanical sensors for bacteria.

Direct and non-invasive measurement of the pressure distribution in test sections of a micro-channel is a challenging, if not an impossible, task. Here, we present an analytical method for extracting the pressure distribution in a deformable micro-channel under flow. Our method is based on a measurement of the channel deflection profile as a function of applied hydrostatic pressure; this initial measurement generates ‘constitutive curves’ for the deformable channel. The deflection profile under flow is then matched to the constitutive curves, providing the hydrodynamic pressure distribution. The method is validated by measurements on planar microfluidic channels against analytic and numerical models. The accuracy here is independent of the nature of the wall deformations and is not degraded even in the limit of large deflections, ${\zeta }_{max} / 2{h}_{0} = O(1)$ , with ${\zeta }_{max} $ and $2{h}_{0} $ being the maximum deflection and the unperturbed height of the channel, respectively. We discuss possible applications of the method in characterizing micro-flows, including those in biological systems.

We developed an organ-on-a-chip platform with integrated stimulators and sensors. The platform is fabricated using direct laser writing (DLW) and allows for generation and study of functional 3D cardiac microtissues in controlled microenvironments.