Liquid crystal droplets as a hosting and sensing platform for developing immunoassays

Abstract

Protein immunoassays generally consist of the immobilization of the proteins on solid surfaces followed by binding with their antibodies. Such systems often require several washing and processing steps which are both time consuming, costly and labor intensive. In this study, we developed an immunoassay in which the proteins are directly immobilized on the surface of the 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 incubation of IgG-decorated LC droplets in an aqueous solution containing 50μg/mL of anti-IgG (AIgG) for 15 min, the orientation of the LCs changed from a radial to a bipolar configuration. In contrast, the orientation of the LCs remains unchanged after the incubation in an aqueous solution containing anti-HSA (AHSA) of the same concentration. We conclude that the bipolar configuration of LCs is a signature of the presence of specific antigen-antibody pairs on the surface. By using this immunoassay, we successfully detect protein concentrations as low as 0.005μg/mL for IgG and 0.01μg/mL for HSA. This is more sensitive than current immunoassays on solid surfaces. In addition, the immunoassay has a dynamic range of 104. These results demonstrate the potential of using LC droplets as sensing platforms for the development of rapid and low-cost immunoassays.