Integrated sample preparation and sensing: Microresonator optical sensors embedded in digital electrowetting microfluidics systems

The intimate integration of digital electrowetting microfluidics and optical microcavity sensors results in an excellent platform for low power consumption, high sensitivity integrated sample preparation and testing, which is particularly useful for medical diagnostics and water quality testing. In this work, a microresonator structure with a buried channel waveguide (resulting in an external Q factor of 28,000 in silicone oil and 17,000 in water) was embedded in the top plate of a digital electrowetting system, enabling sensing with a single droplet of <;100 nL volume. The integrated system was used to successfully demonstrate resonant optical wavelength shifts proportional to index of refraction changes of the liquid actuated to the sensor.