| Microfluidic systems for chemical and biochemical analysis promise increased process portability, speed, and efficiency as well as decreased waste. One important aspect of microfluidic design is the incorporation of immobilized biomolecules in microfluidic devices. Of the methods that have been proposed for the microfluidic immobilization of biomolecules, few allow for reversible immobilization or end-user control over the immobilization process. The absence of these capabilities limits device flexibility and reusability.; Presented in this dissertation is a method for achieving the reversible, controlled immobilization of biomolecules in microfluidic devices. This method is based on so called “smart beads”: latex nanobeads coated with the temperature-responsive smart polymer poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm exhibits lower critical solution temperature (LCST) behavior: soluble in aqueous solutions at room temperature, but becoming hydrophobic and reversibly aggregating at temperatures greater than ∼32 ϒC. Similarly, 100 nm diameter polystyrene latex beads coated with PNIPAAm form a suspension that flows easily through a microfluidic channel constructed from poly(ethylene terephthalate) (PET) at room temperature, but when the temperature of the channel is elevated above the polymer LCST, the beads aggregate and adhere to the channel walls. This adhesion is stable in the presence of flow, and reversible upon return of the channel temperature to below the polymer LCST. By co-modifying PNIPAAm-coated beads with biotinylated poly(ethylene glycol), we have made possible the controlled, reversible immobilization of diverse biomolecules.; Experiments preliminary to the development of the smart bead system described in this dissertation include the study of a PNIPAAm-based bioseparation scheme as well as the investigation of the behavior of PNIPAAm in microfluidic channels. Smart bead applications include an affinity chromatography system, in which the biotinylated beads serve as a chromatographic matrix for the separation of streptavidin from a flow stream, and an immunoassay system, in which beads modified with an antibody for the drug digoxin serve as the substrate for a competitive digoxin immunoassay. Further prospective applications of the smart bead system, such the facilitation of multiple parallel bioseparations in a single microfluidic channel, are also presented. |
