Application of elastin-based nanoparticles displaying antibody binding domains for a homogeneous immunoassay

Nanoparticles are small size-controlled particles from 1 to 100 nm diameters and characterized by their structure, base material and functional units displayed on their surfaces. In this study, protein-based nanoparticles composed of a hydrophobic elastin-like peptide unit, a hydrophilic aspartic acid-rich peptide unit and displaying antibody binding domains on their surfaces, were designed and genetically synthesized. The constituent fusion proteins, termed ELP-D-C, were found to exist in monomeric form (ELP-D-C/monomer) at low temperature. Above the phase transition temperature, however, ELP-D-C was found to rapidly self-assemble to form spherical micelles (ELP-D-C/micelle) with a hydrophobic core and diameters of ∼40 nm. Furthermore, ELP-D-C/micelle were shown to display antibody binding domains on their surfaces, which allowed for immobilization of antibodies and subsequent formation of large, visually detectable complexes in the presence of target molecule (antigen), whose sizes increased in proportion to the target molecule concentration. The observed target molecule concentration-dependent complex formation suggests that ELP-D-C/micelle may be useful as base particles in applications such as homogeneous turbidity immunoassays.