Developing optofluidic technology through the fusion of microfluidics and optics

Abstract

We describe devices in which optics and fluidics are used synergistically to synthesize novel functionalities. Fluidic replacement or modification leads to reconfigurable optical systems, whereas the implementation of optics through the microfluidic toolkit gives highly compact and integrated devices. We categorize optofluidics according to three broad categories of interactions: fluid-solid interfaces, purely fluidic interfaces and colloidal suspensions. We describe examples of optofluidic devices in each category.Optofluidics refers to a class of optical systems that are synthesized with fluids. Fluids have unique properties that cannot be found in solid equivalents, and these properties can be used to design novel devices. Examples of such properties include: the ability to change the optical property of the fluid medium within a device by simply replacing one fluid with another; the optically smooth interface between two immiscible fluids; and the ability of flowing streams of miscible fluids to create gradients in optical properties by diffusion. Most optical systems are currently made with solid materials such as glasses, metals and semiconductors, but there are cases in which it has been advantageous to use fluids. The oil-immersion microscope 1 , liquid mirrors for telescopes 2 , liquid-crystal displays 3 and electrowetting lenses 4 are good examples. Here we describe the various methods used to implement optofluidic devices with recently developed microfluidic technologies that allow accurate control of liquids on small spatial scales. Integration and reconfigurability are two major advantages associated with optofluidics. Whereas microfluidics has made it possible to integrate multiple fluidic tasks on a chip, most optical components, such as the light source, sensors, lenses and waveguides, remained off the chip. Optofluidic integration combines optics and microfluidics on the same chip by building the optics out of the same fluidic toolkit. The second advantage of optofluidics lies in the ease with which one can change the optical properties of the devices by manipulating fluids.Microfluidics is a burgeoning field with important applications in areas such as biotechnology, chemical synthesis and analytical chemistry. Many of these applications of microfluidics are discussed elsewhere in this issue, and for the purposes of this Review we emphasize only a few salient points. First, there is now an extensive body of literature on how the physical properties of fluids that are available only on small spatial scales can be exploited for device functionality [5][6][7] . Many of these effects can also be used to control optical properties. Second, technological advances in device fabrication have made it possible to build miniaturized devices with complex networks of channels, valves, pumps and other methods of fluidic encapsulation and manipulation 8 . This creates a powerful set of tools for fluidic control, and because the feature sizes in these systems are shrinking over time, they will inevitably appro...

A Facile Method for Permanent and Functional Surface Modification of Poly(dimethylsiloxane)

“…It is impossible, however, to have one material that meets all the individual needs of microfluidic systems, 1 micro-electromechanical systems (MEMS), 2 and cellular study. 3 New materials have been developed to replace PDMS.…”

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

“…This is due to the inherent Poiseuille-like flow profiles [8,201] of isotropic fluids. Explorations beyond this Poiseuilledetermined regime could open new microfluidic phenomena and applications [218,219]. Although experimental investigations of complex fluids in microfluidic confinements have been initiated [31,38,39,220,221], understanding of their dynamics is mostly limited to numerical studies [222][223][224][225][226][227][228].…”

Microfluidics

“…This is shown schematically in the top part of Figure 3 with a photograph of the finished structure below. even complex "optofluidic" circuits [7], integrating waveguides as well as photonic crystal structures, light sources and sensors, are utilized to exploit the variability of optical parameters of liquid media in a microfluidic device. The progress of integration even led to dye lasers in a microfluidic device [8].…”