Analytical Products

1. Background Information

Protein A is a protein isolated from Staphylococcus aureus type A, with a molecular weight of approximately 42 kDa. It contains five structural domains (E, D, A, B, and C) that can specifically bind to the IgG molecules of antibodies.

Leveraging the high affinity between Protein A and antibody IgG, Protein A is covalently coupled to purification media and is widely used in the production and purification processes of antibody-based biologics. However, the use of Protein A in antibody purification inevitably leads to some degree of leaching, resulting in Protein A being present as an impurity in the final antibody drug product. For therapeutic applications of antibodies, it is essential to minimize Protein A residues to avoid potential adverse effects on patients. The 2020 edition of the Chinese Pharmacopoeia Volume III, in the "General Principles for Human Recombinant Monoclonal Antibody Products" and the monographs for two monoclonal antibody products—"Nimotuzumab Injection" and "Conbercept Ophthalmic Injection"—specifies requirements for Protein A residue testing. The U.S. FDA and Chapter <130> of the United States Pharmacopeia also provide guidelines for Protein A residue testing.

2. Product Applications

The Protein A Residue Detection Kit (Enzyme-Linked Immunosorbent Assay) produced by our company is a highly sensitive detection kit. It accurately recognizes Protein A ligands from various imported and domestic purification media, enabling sensitive and precise detection of Protein A residues in biological products. It is also suitable for Protein A ligand manufacturers to monitor the leaching of Protein A ligands.

Applicable Protein A ligands include: 1# Standard, 2# Standard, etc.

1# Standard: Suitable for detecting the leaching of Protein A ligands from our AT Protein A Diamond, AT Protein A Diamond Plus, and AT Protein A Diamond Ultra affinity media.

2# Standard: Suitable for detecting the leaching of Protein A ligands from our Novo-A Diamond and Extrem A Diamond affinity media.

3. Product Features

• High versatility, compatible with multiple recombinant and alkali-resistant Protein A residue detections.
• High sensitivity, with the OD ratio of 0 ng/mL to 0.16 ng/mL on the standard curve ranging from 2 to 5 times.
• High precision, with inter- and intra-batch variation < 10%.
• The sample pretreatment method uses acid treatment, eliminating the need for complex heating, centrifugation, and other steps. Additionally, capture antibody, antigen, and detection antibody are incubated simultaneously, removing the need for multiple washing steps, thus simplifying the workflow.
• Excellent stability—the kit shows no significant performance change after 1 month at 37°C, though we recommend storage at 2–8°C.

4. Detection Principle

This kit is based on a double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) to quantify Protein A residues in samples. Samples containing Protein A are first diluted with the provided Sample Diluent, followed by the addition of Denaturing Buffer and thorough mixing to dissociate Protein A from the sample antibodies. The denatured sample is then added to a microplate coated with polyclonal anti-Protein A capture antibodies. A second anti-Protein A detection antibody, directly conjugated to horseradish peroxidase (HRP), forms a solid-phase antibody–Protein A–enzyme-labeled antibody sandwich complex. After a wash step to remove any unbound reagents, the complex reacts with tetramethylbenzidine (TMB), causing a color change from colorless to blue, which finally turns yellow upon the addition of Stop Solution. Absorbance (OD value) is measured at 450 nm and 650 nm, and the OD value is positively correlated with the amount of Protein A in the sample.

5. Kit Component

6. Storage

Preserved at 2-8℃.

7. Ordering Information