Competitive ELISA Affinity Determination Services

Competitive ELISA is a simple and convenient method for affinity determination. The principle is that after the antibody is mixed with antigens with different concentrations, it is incubated in the water solution to reach equilibrium, and the unbound antibody is captured by the antigens contained in the microplate and detected by the ELISA method. At present, there are many commonly used methods to detect affinity, but most of them either rely on expensive equipment, or are not widely applicable or need to modify the antigen, while the competitive ELISA method to determine affinity is not the case, it only relies on a small number of purified antigens and antibodies to detect affinity.

KMD Bioscience is committed to affinity testing research, which can provide customers with professional and effective pre-sales technical consultation and accurate data support and provide strong guarantees for customers' experimental projects.


Principle of Competitive ELISA method:


Competitive ELISA determines the amount of an analyte in a sample by quantifying its interference with the expected signal.

The binding of antigen-antibody is a reversible reaction: [A]+[B]⇋[AB] ([A] represents antibody, [B] represents antigen, [AB] represents antigen-antibody conjugate). When the reaction reaches equilibrium, the dissociation constant Kd=[A][B]/[AB], where [AB] represents the concentration of antibody-antibody conjugate at equilibrium, [A] represents the concentration of free antibody at equilibrium, and [B] represents the concentration of free antigen at equilibrium.

① When there were few antibodies and excessive antigens in the reaction system, the reaction was balanced [AB]>[A].

② When the amount of antigen in the reaction system is small and the amount of antibody is excessive, the reaction reaches the equilibrium [AB]<[A];

③ When the amount of antigen and antibody in the reaction system is just right, the reaction reaches the equilibrium state of half-fullness, then [AB]=[A], Kd=[A][B]/[AB]=[B].

In the state of semi-satiety , if the antibody concentration is very low, the antigen consumed by the reaction is very small, and the concentration of free antigen after the reaction is approximately equal to the total antigen concentration. Thus, under the condition of low antibody concentration, the dissociation constant can be obtained by finding the antigen concentration that can reach the semi-satiety state after reaction equilibrium.


Figure 1 Schematic diagram of competitive ELISA


Technical Feature:


-- Detect crude oil or impure samples without sample handling.

-- Good repeatability: Less difference between repeated samples and analyses.

-- High flexibility: It can be based on direct, indirect or sandwich ELISA. 

-- More robust: Less sensitive to sample dilution and sample matrix effects than sandwich ELISA.


Sample Requirements:


Customer provides


Customer can provide antibody/protein/peptide etc.

* Buffer solution: PBS, HEPPS etc. Try not to contain glycerol, imidazole, trehalose or other salts; try to avoid reagents with amino groups such as Tris as a buffer.

* Protein sample (including antibody): >200ug, concentration >0.5mg/ml, purity >90%.

* Small molecule compound: 1mg, concentration >1mg/ml, purity >90%, soluble in 100%DMSO or water.


Service Highlights:


-- Professional technical team and rich technical experience

-- High detection efficiency, no labeling, real-time monitoring

-- Advanced instruments and equipment

-- A wide range of applications: can be used for protein, nucleic acid, peptides, nanomaterials and other molecular interaction analysis

-- One-stop service: from affinity measurement services to molecular interaction research integrated solutions


How to Order?

If you have any questions regarding our services or products, please feel free to contact us by E-mail: or Tel: +86-400-621-6806