Multiplex pressure measurement in microsystems using volume displacement of particle suspensions

We demonstrate a simple image-based method to measure pressure in microsystems using volume displacement of fluorescent particle suspensions. These micro pressure-sensors are composed of two layers with a poly(dimethylsiloxane) (PDMS) membrane in between: the flow layer includes a flow channel and the sensor layer contains a detection channel filled with suspensions of fluorescent particles. The pressure increase in the flow channel deflects the membrane, and this membrane deformation can be quantified by measuring the cross-sectional areas at specific focal planes. These simple sensors have the advantage that a broad sensing-range can be achieved by tuning the mechanical property and the geometry of the membrane during design and fabrication, and even simpler by tuning the focal plane or the pressure of a reference chamber while in operation. We also demonstrate here a pressure transduction scheme coupled with the image-based sensing method as a multiplex pressure measurement tool for simultaneously detecting pressures in multiple locations in a microsystem. Overall, the image-based pressure sensing method has high precision when operated in both direct and remote detection modes. Compared to conventional mechanical methods of pressure detection, this technique is inexpensive because it does not require complex off-chip equipment to quantify the pressure-dependent membrane deformation. In addition, the image analysis using the software code developed here is fast, and it generates data that are simple to interpret.