(175f) Using Elastohydrodynamic Deformation for Non-Contact Measurements of Flow and Particles with Graphene Nanoisland Sensors

Microfluidics have served as a powerful platform for sensing a wide range of phenomenon, from physical to biological. A major pitfall, however, is that microfluidic systems are very expensive and often require microscopes, antibodies and vibration isolation. This means that while a single microfluidic device may be cheap, the platform can become prohibitively expensive when considering multiple devices. We report a novel way to evaluate microfluidic devices by measuring flow and particles through the deformation of the soft channel walls. This fluid-induced deformation (elastohydrodynamics) increases in proportion to the flow rate or viscosity, and in addition, changes as particles pass along in the channel. This technique differs from using micropatterned features, which interact with the substrate and can still require expensive platforms to evaluate – we deploy an ultra-sensitive (< 0.001% strain), but easy to fabricate, metallic (palladium) nanoisland-on-graphene composite. These sensors are evaluated using a simple voltage measurement and forgo the need for expensive optical equipment. We also discuss the underlying theory behind device operation and report experimental validation of a rigid sphere moving in a proximity to a deformable wall under pressure-driven flow.

In addition to flow and particle measurements, this technique is a convenient platform to evaluate interfacial phenomenon and viscoelastic properties. We measure the transient changes in the channel deformation when pulsed with an air bubble, which allows us to measure the viscoelastic relaxation of the channel. We see agreement between our methods and other techniques in the literature. These devices are widely applicable due to their sensing modality – there is no specialized liquid, or optical demands and we take advantage of this orthogonality through experiments on cells and thin coatings.