Single step diagnosis system using the FRET phenomenon induced by antibody-immobilized phosphorylcholine group-covered polymer nanoparticles

We report here a single step molecular diagnosis system using phosphorylcholine group-covered nanoparticles (PC-NPs). The most favorable characteristics were (i) the suppression of non-specific protein adsorption by the PC group-covered surface and (ii) molecular diagnosis by the capture of the target antigen. The fundamental strategy was based on antigen–antibody reactions on the PC-NPs. In particular, we installed a fluorescence resonance energy transfer (FRET) system on the immobilized antibodies. The immobilized antibody was labeled by donor or acceptor molecules separately, which were fluorescent molecules. These molecules induce the FRET phenomenon if they are close to each other upon capture of the target antigen by the PC-NPs. Therefore, the resulting fluorescence was readable using the FRET phenomenon. In this paper, C-reactive protein (CRP) was used as the target antigen, and the anti-CRP antibody was labeled by fluorescent molecules. The labeled antibody was then immobilized onto the PC-NPs. The resulting fluorescence intensity was well correlated with the change in the concentration of CRP. The protocol for molecular diagnosis is quite simple, and only involves mixing the FRET-installed NPs and target molecules such as CRP. Single step molecular diagnosis via FRET may be of great importance for designing sensor devices.