(306f) Pressure Measurement in Microsystems Using Volume-Displacement of Nanoparticle Suspension

Pressure is widely used to control fluid motions in microsystems. To achieve the accurate pressure measurement inside of microchannels, a number of detection methods have been developed. While most of these methods show high degrees of accuracy, they are not widely applicable for many microsystems due to a few drawbacks, such as size constraint, complications in fabrication, and expensive off-chip equipment. To overcome these limits, we present here a simple image-based method to measure pressure using volume displacement of fluorescent particle suspension. We fabricated microdevices consisting of two layers and polydimethylsiloxane (PDMS) membrane in between: bottom layer includes a flow channel and top layer contains a detection channel filled with fluorescent particles. Pressure increase in the flow channel deflects the PDMS membrane and its deformation can be quantified by software developed in-house. The area in which particles are in- and out-of-focus is measured as a function of pressure. This simple image processing is easy to use and produces data easy to interpret. Using this method, we accurately measured pressure in the range of 0.1 ~ 10 psi. This sensing range can be extended by tuning focal planes or reference pressures. Furthermore, because pressures in various parts of the chip can be transduced and the signals transferred to a single location, we can simultaneously detect pressures in multiple locations of microsystems. This multiplex pressure measurement can improve the throughput of microfluidic devices especially for highly integrated multi-functional devices. Compared to existing techniques, our pressure sensor is very easy to integrate without complicated fabrication processes and its performance can be optimized by simply changing geometry and thickness of the membrane.