Anti-biotin capture system: fast and easy solution for the immobilization and characterization of your biotinylated ligands

The anti-biotin capture system immobilizes biotinylated ligands on an oligonucleotide sensor chip through oligo-conjugated NeutrAvidin. This application note tests it with biotinylated human epidermal growth factor receptor (EGFR) and the therapeutic antibody cetuximab.

The Challenge: Fast Immobilization of Biotinylated Ligands

Biotin can be coupled to proteins, carbohydrates, fluorophores and nanoparticles, which makes it a practical handle for many ligands. For kinetic work, the capture layer must be simple to build and give a controlled ligand density. NeutrAvidin lacks the glycan structures of the original protein, which reduces non-specific binding.

The Approach: NeutrAvidin Adapter, Biotinylated EGFR and Cetuximab

NeutrAvidin-oligo (50 nM) was hybridized to the sensor chip, then 250 nM biotinylated EGFR was captured. Single-cycle kinetics in PBS-T used cetuximab from 0.078 to 5 nM at 250 µL/min, with a final dissociation of 70 minutes. The data from nine molograms in one flow chamber were fitted with a Langmuir 1:1 model.

Key Results for Cetuximab Binding to EGFR

• Capture ratio: a median of 0.5 biotinylated EGFR per NeutrAvidin, likely limited by the size of EGFR (110 kDa) against the adapter (66 kDa).
• Affinity: K_D of 0.326 pM for cetuximab and EGFR, supported by at least 5% dissociation during the measurement.
• Ligand density: an effective 15 pg/mm², or 8.2 × 10⁷ sites/mm², about 0.4% of a protein monolayer.

Why It Matters for Antibody Characterization

Because capture runs through the oligonucleotide sensor chip, the surface can be regenerated with the defined regeneration solution. The low ligand density falls within the optimal range for kinetic studies. The result is a short route from a biotinylated ligand to affinity and kinetic data for analytes such as therapeutic antibodies.