Specific binding of magnetic nanoparticle probes to platelets in whole blood detected by magnetorelaxometry

The binding of monoclonal antibodies labelled with magnetic nanoparticles to CD61 surface proteins expressed by platelets in whole blood samples was measured by magnetorelaxometry. This technique is sensitive to immobilization of the magnetic labels upon binding. Control experiments with previous saturation of the epitopes on the platelet surfaces demonstrated the specificity of the binding. The kinetics of the antibody antigen reaction is accessible with a temporal resolution of 12 s. The minimal detectable platelet concentration is about 2000 μL−1 (sample volume 150 μL). The proportionality of the magnetic relaxation amplitude to the number of bound labels allows a quantification of the antibody binding capacity.