Flow determination via nanoparticle strain sensors for easy Lab on Chip integration

Abstract

With the advancement of microfluidic and Lab on Chip systems, new challenges arise regarding efficient system monitoring as well as the detailed tracking of fluids within the system’s microfluidic channels. In this paper, a strain-sensing module offering facile integration with most microfluidic-systems is used for the determination of flow in a microfluidic chip. The sensor is based on platinum nanoparticle networks that are produced via a modified-sputtering technique; the nanoparticles self-assemble on top of flexible polyolefin substrates that also serve as the sealing layer of the microfluidic channels (fabricated on printed circuit board substrates or PCBs, by means of milling and computer numerical control machining). By introducing varying flow rates, pressure within the microfluidic channel increases thus resulting in the straining of the polyolefin layer and in modifying the resistance of the module. Numerical calculations, which take into account the bidirectional connection of fluid flow with the deformation of the sealing layer, are used to extract the channel geometry maximizing the sealing layer strain. Flow determination or flow-sensing experiments have also underlined the importance of polyolefin to PCB bonding-strength, which was greatly improved by oxygen plasma treatment. The module is able to detect flow rates as low as 5 μL/min, corresponding to a strain of 0.00337%, and showing a sensitivity of 0.021 (μL/min)−1, showcasing a) a competitive limit of detection (LoD), and b) low-cost, low-power requirements and easy integration with existing microfluidic systems, either as an autonomous unit or by integrating it on its sealing material.