Determination of active antigen concentrations using complementary label-free methods.

<p>(A) Titration-based Octet measurement obtained over immobilized anti-Id mAb for samples containing 1 nM DS4 binding sites titrated with a purified preparation of carrier-free human DKK4. (B) Sharp inhibition curve obtained from the data shown in panel A showing that a nominal concentration of 50 nM human DKK4 was needed to exactly titrate out 1 nM DS4 (corresponding to an antigen activity of 2%). (C) CFCA data collected on the Biacore for a nominal concentration of 0.1 µg/mL human DKK1 flowed at 100 µL/min (blue) and 5 µL/min (red) over a high capacity of immobilized DS4. The curve fit is shown in black.