Extraction of C-reactive protein from serum on a microfluidic chip

The first extraction of a protein, C-reactive protein (CRP), from unadulterated serum on a microfluidic chip is demonstrated. Two stationary phases were evaluated for their ability to selectively extract this protein directly from serum without the need for additional cleanup steps. The first extraction media tested was an affinity matrix containing monoclonal antibodies to CRP, however, after immobilization this media failed to bind CRP. The more efficient stationary phase, immobilized phosphocholine, extracted CRP in a Ca2+-dependent manner. Significant non-specific binding by more abundant serum proteins was observed using typical washing protocols with this phase and these protocols were modified and optimized to yield extractions that were selective to phosphocholine-binding proteins. Extraction efficiencies were 40% for standard CRP solutions and run-to-run extraction reproducibility was 15% for 8 μL of total serum loaded. Serum concentrations of CRP determined by this method in patients who had undergone hip replacement surgery compared favorably with those values obtained by the conventional, currently utilized methods. Thus, this newly developed miniaturized method for protein purification from serum will provide a foundation for future extractions of protein biomarkers.