(76b) All-Optical Microfluidic Biosensor

Advances in microfluidics and lab-on-a-chip technology have accelerated the development of compact and portable biosensors for point-of-care applications. A relatively new and promising approach to such sensors involves optofluidics where optic and fluidic functionality are integrated at the microscale to leverage their combined advantages. Microfluidic functionality enables compact and rapid processing of small specimens, and optical functionality enables high detection sensitivity of target biomaterials within these samples. In this presentation we introduce a novel all-optical microfluidic biosensor concept. The sensor consists of substrate with an array of embedded microchannels carrying fluid flow perpendicular to its surface. There is a central microchannel and secondary microchannels symmetrically aligned with a periodic spacing about this channel. The central microchannel is illuminated with a focused beam of light propagating perpendicular to the substrate. The periodic spacing of the channels and contrast in refractive index between the fluid and the substrate act to confine and guide the incident light down through this channel. The transmission spectrum through the sensor exhibits minima that depend on the dimensions, periodicity and refractive index of both the carrier fluid and the substrate material. Sensing is achieved via accumulation of a thin layer of target biomaterial on the surface of the microchannel walls, which are functionalized to bind with the material as it flows through the system. The presence of the biolayer causes a shift in the optical transmission minima. We study this effect at optical wavelengths as a function of device parameters and material properties. We also use computational fluid dynamics to model fluid flow through the sensor. Our analysis demonstrates that detectible shifts in the transmission spectrum can be achieved with nanoscale accumulation of biomaterial within the sensor and with relatively little refractive contrast between this material and carrier fluid. The transmission mode operation of the sensor can enable multiplexed biosensing on a single sensor platform.