In-line pressure monitoring for microfluidic devices using a deformable diffraction grating

In this paper, a novel optical method for monitoring of local pressure in a microfluidic device using a deformable diffraction grating is presented. A test device was fabricated with transparent silicone elastomer-polydimethylsiloxane (PDMS)-using the replica molding technique. A diffraction grating of 2 mm/spl times/2 mm area and a microchannel of 200 /spl mu/m width and 20 /spl mu/m depth are defined by the conformal contact between a PDMS chip and a glass plate. The grating consists of 5 /spl mu/m wide, 2 /spl mu/m deep rectangular grooves arrayed with period of 10 /spl mu/m, and it is connected to access ports with the microchannel. Optical response of the device to internal pressure ranging from 0 to -80 kPa is presented and compared with theoretical prediction. It is also demonstrated that the test device can be used for measurement of air flow rate ranging form 0 to 0.3 cc/min. The major advantages of this method are simple fabrication and flexible design. This method is not only desirable for flow characterization of microfluidic devices, but also opens up the possibility of new types of fiber-optic pressure sensors and pressure-driven optical modulators.