Multiple Protein-immobilized Phospholipid Polymer Nanoparticles: Effect of Spacer Length on Residual Enzymatic Activity and Molecular Diagnosis

We report the development of phosphorylcholine (PC) group-covered nanoparticles for multiple immobilization reactions; the surface of these nanoparticles facilitates bioreactions such as enzymatic reactions and molecular diagnoses. The nanoparticles were covered with a bioconjugate PC group containing a polymer backbone, and their surface properties were as follows: (1) suppression of nonspecific protein adsorption and (2) stabilization of immobilized biomolecules. In this study, biomolecules were immobilized on PC-covered nanoparticles by using different spacer lengths between the polymer backbone and biomolecules. The stability of the immobilized biomolecules was evaluated using horseradish peroxidase-labeled IgG, and the bioconjugate nanoparticles were stored at 4, 25, and 40 °C. The residual enzymatic activity of the peroxidase was monitored at a particular time. On the other hand, to test the role of these nanoparticles in molecular diagnosis, we used IgG-conjugated nanoparticles and the fluorescence resonance energy transfer (FRET) phenomenon. The IgG molecules were labeled with either donor or acceptor molecules, and each labeled IgG was simultaneously immobilized on the PC-covered nanoparticles. These labeled IgG molecules induce the FRET phenomenon upon capture of the target antigen provided they are in close proximity. The resulting fluorescence was readable via the FRET phenomenon. In the present study, C-reactive protein (CRP) was used as the target antigen, and the effect of the spacer length is discussed. The bioconjugated nanoparticles covered with PC groups are promising tools for tuning bioreactions.