(203a) Liquid Crystal Droplets as Platforms for Developing Immunoassays

Protein immunoassays generally consist of the immobilization of the proteins on solid surfaces followed by binding with their antibodies. Such systems often require several rinsing and washing steps which are both time consuming and labor intensive. In this study, we developed an immunoassay in which proteins were directly immobilized on the surface of liquid crystal (LC) droplets rather than on solid surfaces. The advantage of this assay is that the binding of antibodies to the surface-immobilized proteins can be transduced by the LC droplets without the need for additional steps for developing readout signals. For example, we observed that after 15 min immobilization of 50µg/mL AIgG with IgG-decorated LC droplets, the orientation of the LCs changed from a radial (perpendicular) to a bipolar (tilted) configuration. In contrast, the orientation of the LC remains to be radial after the immobilization with a non-paired antibody solution (AHSA). The same holds true for HSA-AHSA pair. We conclude that the bipolar configuration of LCs is a signature of the presence of specific proteins present on the surface. We were able to detect protein concentrations as low as 0.005µg/mL for IgG and 0.01µg/mL for HSA which is more sensitive than current solid immunoassays. In addition, the immunoassay has a dynamic range of 10⁴. Also, because the orientations of the LCs are initially induced to a radial configuration, droplet sizes are not critical in the investigation. These results suggest new approaches in improving the design of immunoassays, thereby reducing the processing steps and the analysis time.