Detection of C-Reactive Protein Utilizing Magnetic Permeability Detection Based Immunoassays

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Abstract
A new sensing technology platform integrating magnetic permeability detection and a two-site heterogeneous immunoassay in a one-step analysis is described. As a platform model, measurements of C-reactive protein (CRP), a cardiac and inflammation marker, were performed in a rapid (11.5 min) high-sensitivity (hs) procedure with a low detection limit (0.2 mg/L) and accuracy (CV = 11%). The two-site heterogeneous immunoassay was performed in 1.2-mL disposable reagents vials containing solid phase (polyclonal anti-CRP conjugated silica microparticles), labeling agent (monoclonal anti-CRP conjugated superparamagnetic nanoparticles), and reaction buffer. Whole blood (20 μL) was assayed by introducing the sample into a reagent vial using a glass capillary and mixing its contents by hand for 30 s. After a 11-min sedimentation step, the vial was placed into the coil of the magnetic permeability detector, which measured the enrichment of superparamagnetic nanoparticles in the solid-phase sediment. Magnetic permeability detection and quantification is based on the principle that when paramagnetic materials are placed inside a coil, the inductance of the coil is influenced. Screening of CRP on whole blood patient samples showed good correlation with central hospital measurements for hsCRP (y = 1.018x − 0.021, R2 = 0.980, n = 103) and normal range CRP (y = 1.02x + 2.53, R2= 0.991, n = 33) analyses. The mean differences of the two methods according to the Bland and Altman plots were −0.03 ± 1.12 mg/L for hsCRP analysis and −3.4 ± 8.64 mg/L for normal range CRP analysis.