Novel Flow Control Schemes Utilizing Intrinsic Forces on Centrifugal Microfluidic Platforms

Fluidic functional tools such as lysis, valving, and volume definition have been developed to facilitate the implementation of biological and chemical assays on microfluidic discs. Many of these functional tools require external sources of energy such as thermal energy for operation. To reduce cost and increase reliability and portability of centrifugal microfluidic platforms we have explored the design and operation of three novel fluidic processes that rely on the intrinsic forces of the spinning platforms to perform novel valving, volume definition, and fluid transport on a rotating disc. The first technique is based on the activation of a hydrophobic siphon by the negative pressure (suction) generated along a radial micro-channel as a fluid moves through it. This technique allows the creation of a "hydrophobic siphon"; a previously believed impossible valving mechanism on discs made with hydrophobic materials. Besides valving, this "hydrophobic siphon" design allows drawing fluid toward the disc center for short distances and mixing of liquids. The second functional tool solves one of the major deficiencies of centrifugal microfluidics—the inability to move fluids back to the disc center once they have reached the edge of the disc—referred to as "centrifugal micro-pulley" technology. The third technological development introduces the concept of tunable valves; a system of pressure-regulated valves where the sample fluid flow can be controlled by another fluid through a ventless network of channels. The height of the "tuning" fluid column and its density can be selected to "tune" the angular velocity that is needed to flow the sample fluid. This technique can also be used for volume definition of the sample. Other topics such as novel use of liquid polymers on CDs, development of the "world-to-chip" interface for microfluidic discs, and implementation of an advanced dynamic imaging station for study of centrifugal fluidic processes are presented as well. These novel techniques and instruments can enhance the flexibility of fluidic designs for the development of complex assays and allow more cost-effective, energy-efficient, and portable uses of centrifugal microfluidic platforms for in-vitro diagnostics.