A Visual Distance-Based Capillary Immunoassay Using Biomimetic Polymer Nanoparticles for Highly Sensitive and Specific C-Reactive Protein Quantification

The low-cost daily monitoring of C-reactive protein (CRP) levels is crucial for screening acute inflammation or infections as well as managing chronic inflammatory diseases. In this study, we synthesized novel 2-Methacryloyloxy ethyl phosphorylcholine (MPC)-based biomimetic nanoparticles with a large surface area to develop a visual CRP-quantification assay using affordable glass capillaries. The PMPC nanoparticles, synthesized via reflux precipitation polymerization, demonstrated multivalent binding capabilities, enabling rapid and specific CRP capture. In the presence of CRP, PMPC nanoparticles formed sandwich structures with magnetic nanoparticles functionalized with CRP antibodies, thereby enhancing detection sensitivity and specificity. These sandwich complexes were magnetically accumulated into visible and quantifiable stacks within the glass capillaries, allowing for the rapid, sensitive, and specific quantification of CRP concentrations with a detection limit of 57.5 pg/mL and a range spanning from 0 to 5000 ng/mL. The proposed visual distance-based capillary biosensor shows great potential in routine clinical diagnosis as well as point-of-care testing (POCT) in resource-limited settings.