Liquid Crystals and Nanostructured Surfaces: A Novel System for Detecting Protein-Binding Events
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Studies of nanometer-scale phenomena represent one of the most flourished areas in science at the beginning of 21st century. While the early activities have focused on fabricating well-defined nanomaterials and their novel properties, few have demonstrated a workable functional principle that can be developed into tangible applications. On the other hand, the protein binding events that orchestrate the biological activities in living cells (so-called cell signaling pathways( occur at nanometer scale. The protein binding events can be first induced at membrane proteins by either a physical or chemical signal or an internal stimulus such as hormone. The dimerization or phosphorylation of membrane proteins leads to a series of protein binding events in the cytosol. The final binding event in the cytosol may lead to the transport of a protein into the nucleus that induces gene expression to produce a new protein. The new protein expressed signals a biological response in the form of new activities, such as cell death, proliferation, disease, or expression of white blood cells.
Deciphering the protein binding events in such complicated and interconnected signaling pathway will lead to molecular-level understanding of the physiology of living system as well as drug design. However, the scope of the problem demands a rapid and global approach. Because the quantity of protein involved on chip-based assay is little and the detection scheme can be highly parallel, surface-based proteomics tools have the potential to increase the rate of discovery and the scope of investigations aimed at understanding protein function, modification, and regulation in cell signaling processes as well as the study of protein–drug interactions.
This article describes a new detection method for protein binding events by using a well-controlled nanotopography on surface and the unique optical properties (birefringence) of liquid crystals. The development of this method integrated knowledge from multiple disciplines including self-assembled monolayers (SAMs), liquid crystals, protein immobilization, and molecular biology. In the following, the effect surface topography and chemistry on the alignment of liquid crystal is first investigated. Then, the influence of surface-bound proteins on the alignment of liquid crystal is reported. Establishing the response of liquid crystal to surface-bound protein, a general scheme is designed to support biospecific protein binding on surface. Last, the binding activities of the immobilized protein on nanostructured surface toward specific and nonspecific antibodies are detected by the molecular organization (orientations) of liquid crystals in contact with the surfaces where binding occurs.