Figure 3. Specific binding and magnetic adhesion for 3 differently sized magnetic particles as a function of time varying flowrate.

Real time binding curves are acquired for streptavidin-coated magnetic particles of different sizes: (a) Miltenyi MACS (50 nm, c = 2 · 10¹² particles/mL), (b) RnD MagCellect (150 nm, c = 6 · 10¹⁰ particles/mL), (c) Ademtech Bio-Adembeads (300 nm, c = 1.2 · 10¹⁰ particles/mL). The particles get captured either by biotin-BSA coated sensors (combination of specific binding and magnetic adhesion, blue curves) or by BSA coated sensors (magnetic adhesion only, red curves). Flowrates are changed about every 3 minutes (indicated in different shading). The specific binding portion (temporal asymptotic value of the exponential fit of the difference between blue and red curves in a,b,c) and a magnetic adhesion noise estimate (three times standard deviation of slope-removed data), both extracted from (a,b,c) are plotted in (d,e,f). All data is acquired in parallel microfluidic channels on the same GMR sensor die. Error bars denote sample standard deviation.