Optical properties microfluidic devices

The objective of nanoscale optofluidic charac-terizatimi is to combine different nanophotonics technologies with microfluidic devices and thereby explore and develop photonic analysis techniques based oti the microscopic flows of liquids and on nanophotcHiic properties. The optofluidic character-izatimi techniques will be powerful new tools for a wide range of applications in optical information processing and the miniaturizatimi of chemical and biological processes for synthesis, analysis, and recognidOTi [1]. 

The concept behind optical devices which incorporate liquids as a fundamental part of the optical structure can be traced at least as far back as the eighteenth century where rotating pools of mercury were proposed as a simple technique to create smooth spherical mirrors for use in reflecting telescopes. Modem microfluidics has enabled the development of a present-day equivalent of such devices, the development of which we now refer to as optofluidics. As will be described below, the capabilities in terms of fluidic control, mixing, miniaturization, and optical property tuning afforded by micro-, nano-, and electro-fluidics combined with soft lithography-based fabrication provide an ideal platform upon which to build such devices. 

The materials used for the fabrication of most microfluidic chips include glass, silicon, quartz, and plastics ( Materials Used in Microfluidic Devices) In addition to cost and optical, electric, and physical properties, careful consideration must be given to the surface chemistry of the material ( Surface Modification, Methods). In fact, surface chemistry plays a major role in chemical cytometry, as protein adsorption to the channel walls can degrade the separation performance and make the electroosmotic flow unreproducible. 

Conventional polymers do not always possess the combination of desired bulk and surface properties for a specific application. The polymer materials used for microfluidic devices are innately hydrophobic, low-surface-energy materials and thus do not adhere weU to other materials brought into contact with them. This necessitates their surface modification/treatment to render them adhesive. This has prompted the development of a variety of polymer modification techniques, with the aim of developing new materials from known and commercially available polymers that have desirable bulk properties (elasticity, thermal stability, permeability, etc.) in conjunction with newly tailored surface properties (adhesion, biocompatibUity, optical reflectivity, etc.). 

PDMS emerged as the polymer of choice for micropatterned surfaces and microfluidic devices. Fabrication is particularly straightforward since PDMS can be cast against a suitable mold with high fidelity. The optical, thermal, interfacial, permeability, and reactivity properties of PDMS make possible numerous functionalities including optical detection, reversible deformation, reversible wetting, and management of cell proliferation. "... 

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