A polydimethylsiloxane (PDMS) deformable diffraction grating for monitoring of local pressure in microfluidic devices

In this paper, a novel optical method for monitoring of local pressure in microfluidic devices using a deformable diffraction grating is presented. A test device was fabricated with transparent silicone elastomer-polydimethylsiloxane (PDMS)-using the replica moulding technique. The moulded PDMS chip and a flat glass plate have a bonding interface, which defines a 2 mm x 2 mm diffraction grating and a 200 mum wide, 20 mum deep microchannel. The grating consists of 5 mum wide, 2 mum deep rectangular grooves arrayed with a period of 10 mum. All the grooves are connected to the microchannel, and deformed by internal pressure. The optical response of the device to pressure ranging from -80 to 100 kPa is presented and compared with the theoretical prediction. It is also demonstrated that the test device can be used for measurement of air flow rates ranging from 0 to 0.3 ml min(-1). The major advantages of this method are simple design and inexpensive fabrication. This method is not only desirable for flow characterization of microfluidic devices, but also opens up the possibility of producing new types of fibre-optic pressure sensor and pressure-driven optical modulator.