Optics-Free, Non-Contact Measurements of Fluids, Bubbles, and Particles in Microchannels Using Metallic Nano-Islands on Graphene

Abstract

<p class="first" id="P2">Despite the apparent convenience of microfluidic technologies for applications in healthcare, relatively few devices are in commercial development because they often rely on capital-intensive optics and other peripheral equipment that limits throughput. Here, we evaluated fluids, gases and particles as they flowed through a microfluidic channel without the use of a camera or laser, which we call “optics-free” microfluidics. We did this by monitoring the deformation caused by the analyte on the channel side walls. This minute deformation was transduced into a simple resistance measurement by using an ultra-sensitive piezoresitive film comprising metallic nanoislands on graphene. We were able to relate changes in the resistance of the sensor to the theoretical deformation of the channel at varying flow rates. Then, we used air bubbles to induce a perturbation on the elastomeric channel walls and measured the viscoelastic relaxation of the side channel. We obtained a viscoelastic time constant of 11.3±3.5 s ⁻¹ for polydimethylsiloxane, which is consistent with other techniques. Finally, we flowed silica particles and human mesenchymal stem cells and measured the deformation profile on the channel. These experiments represent a convenient, continuous, non-contact measurement of either rigid or deformable particles, without the use of a laser or camera. </p><p id="P3"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/2d3a3d21-9eb3-4ecf-83d7-98e4266094b6/PubMedCentral/image/nihms-990655-f0001.jpg"/> </div> </p>