A novel approach to ultrasensitive diagnosis using supramolecular protein nanoparticles

We report on the ultrasensitive protein nanoprobe system that specifically captures disease marker ( autoantibodies of Type I diabetes in this case) with attomolar sensitivity. The system relies on supramolecular protein nanoparticles that bind a specific antibody [ 65 kDa glutamate decarboxylase ( GAD(65))- specific autoantibody, i.e., the early marker of Type I diabetes]. The ultrasensitive detection of early marker of Type I diabetes during the early phase of pancreatic beta-cell destruction is important because individuals at high risk of developing Type I diabetes can be identified several years before the clinical onset of the ailment. The bacterial expression of chimera genes encoding N-[human ferritin heavy chain (hFTN- H)]::[ specific antigenic epitope]- C produces supramolecular nanoparticles with uniform diameters ( 10 - 15 nm), owing to self-assembly activity of hFTN- H. Each nanoparticle, formed by intermolecular self-assembly between the chimera protein molecules, is subjected to carrying a large number ( presumably, 24) of epitopes with a homogeneous and stable conformation per autoantibody binding, thereby allowing substantial enhancement of sensitivity. The sensitivity was finally boosted to 3 attomolar concentration of the autoantibodies, 4 - 9 orders of magnitude more sensitive than conventional immunoassays. Also, this ultrasensitive protein nanoprobe successfully detected natural autoantibodies in the sera from Type I diabetic patients. The attomolar sensitivity was successfully reproduced on the detection of other antibodies, i.e., monoclonal antibodies against hepatitis B surface antigen. With the two antibody markers above, the feasibility of simultaneous and multiplexing-mode detection was also demonstrated.