Particle Detection in Fluids with Microfluidic Mechanical Resonator Circuits
Benjamín Alemán, Physics

More than one billion people world-wide, many of whom live in low-resource rural settings, lack access to basic health care services and clean drinking water, while millions die each year from exposure to lethal viruses or bacteria. Portable systems for fast, reliable and easy-to-use medical diagnostics and environmental monitoring have been identified as a critical need to address this significant global health problem. Essential to such systems is the rapid and accurate detection, identification, and sorting of micro and nanoscale particles within a fluid. These sensing capabilities are also of great importance across the sciences, industry, and medicine. In medicine, for example, small particle detection in fluid is crucial to the most common medical diagnostic tools including blood chemistries, cell counting, infectious agent detection, and immunoassays. Existing approaches to count or determine size distributions of small particles in fluids (e.g. optical microscopy, dynamic light scattering, or centrifugation) involve resource-heavy and physically large, immobile instrumentation and thus are incompatible with portable sensing systems; furthermore, these approaches tend to be slow, require large fluid volumes, have poor sizing resolution, or require the extraction of particles from the fluid sample.

Miniaturized networks of fluid conduits, or microfluidics, provide a means for in situ monitoring of micro- and nanoparticles in fluid. The small size (microchip-scale) of microfluidics makes them both inherently portable and able to support multiplexing and sophisticated functions such as filtering, mixing, sorting, and analysis. While microfluidics offer many distinct advantages and have excelled at some functions, they continue to fall short as efficient and portable particle analyzers. Key reasons for these deficiencies include cumbersome fabrication of optoelectronic-integrated microfluidics, a reliance on ensembles of auxiliaries such as electronics and pressure regulators, and, most importantly, poorly performing particle sensing mechanisms. We aim to remove these barriers to microfluidic usability through the use of nanodroplet resonances. The objective of this project is to develop, fabricate, and test an innovative microfluidics-based analyzer for high-speed, high-resolution particulate detection in fluids amenable with full portability. At the core of this novel approach and the invention is a microfluidic circuit possessing a sharp mechanical resonance whose tuning frequency, in analogy to an electronic radio circuit, is highly sensitive to the presence of a particle in the circuit. By addressing the fundamental need for high-fidelity, portable fluidic sensing systems, our invention will contribute to environmental (e.g. water quality) monitoring and point-of-care medical diagnostics for rural, modern and military settings. The metrological capabilities of our invention will also be important to many areas of science that require detailed knowledge of small particles (such as biological macromolecules, bacteria, inorganic nanoparticle, etc.) in fluid.