What is the Difference Between Homogeneous and Heterogeneous Immunoassay

The main difference between homogeneous and heterogeneous immunoassay is that homogenous immunoassays are carried out by simply mixing reagents with the sample to take a physical measurement. In contrast, heterogeneous immunoassay involves multiple steps with adding and washing away separate reagents before taking a measurement.

Homogeneous and heterogeneous immunoassays are two types of immunoassays. They measure the presence and concentration of a particular analyte in a solution.   

Key Areas Covered

1. What is Homogeneous Immunoassay
– Definition, Features, Examples
2. What is Heterogeneous Immunoassay
– Definition, Features, Examples
3. Similarities Between Homogeneous and Heterogeneous Immunoassay
– Outline of Common Features
4. Difference Between Homogeneous and Heterogeneous Immunoassay
– Comparison of Key Differences

Key Terms

Heterogeneous Immunoassay, Homogeneous Immunoassay

What is Homogeneous Immunoassay

Homogenous immunoassay is a type of immunoassay in which antigen-antibody reactions occur in a single sample with no separation of antibody-bound components. Importantly, this assay is based on conformational changes of the enzyme’s active site or the substrate’s steric hindrance by binding enzyme-labeled antigen to the antibody. When the analyte binds to the conjugated antibody, a conformational change of the active site of the enzyme or a physical blockage of the enzyme occurs, inhibiting the binding of the analyte to the enzyme. This allows the measurement of the free analyte concentration.

Figure 1: Competitive Homogenous Immunoassay

Furthermore, homogenous immunoassay is important for determining low molecular weight analytes, including hormones and drugs. Also, it is a rapid and sensitive method for detecting protein antigens with a higher molecular weight.  

What is Heterogeneous Immunoassay

Heterogenous immunoassay is a type of immunoassay that involves separate steps for the detection of an antigen present in a sample. These steps may include the precipitation of chemicals, crosslinking with other antibodies, and antibody bound to the solid phase. Here, when the matrix components are washed away, the remaining assay components are added to the final reaction mixture.

Figure 2: ELISA

Importantly, heterogenous assays can determine the presence and the concentration of high molecular weight analytes such as proteins. ELISA is an example of a heterogeneous immunoassay.

Similarities Between Homogeneous and Heterogeneous Immunoassay

• Homogeneous and heterogeneous immunoassays are two types of immunoassays that are biochemical tests that measure the presence and the concentration of a particular analyte in a sample.
• The analyte is often a protein in a biological liquid such as serum or urine.

Difference Between Homogeneous and Heterogeneous Immunoassay

Definition

Homogeneous immunoassay refers to an immunoassay system in which both antigen-antibody reaction and the measurement of the degree of the immune response are performed in solution without separation of the free and antibody-bound components. In contrast, heterogeneous immunoassay refers to the immunoassays that require the separation of the analyte‐antibody complex from the remaining sample before final analysis.

Significance

Homogenous immunoassays are carried out by simply mixing reagents with the sample to take a physical measurement. In contrast, heterogeneous immunoassay involves multiple steps with adding and washing away separate reagents before taking a measurement.

Protocol

Homogenous immunoassay has a shorter and simple protocol, while heterogenous immunoassay has a long and complex protocol.  

Importance

Homogenous immunoassay is important for detecting low molecular weight analytes, while heterogenous immunoassay is important for detecting high molecular weight analytes.

Conclusion

In brief, homogenous and heterogeneous immunoassays are two types of immunoassays that are important in detecting the presence and concentration of analytes in a sample. In a homogenous immunoassay, antigen-antibody reactions occur in a single step by mixing solutions. Therefore, it is a simple and shorter type of immunoassay. Also, homogenous immunoassay is important for detecting low molecular weight analytes. In comparison, heterogenous immunoassay requires multiple steps to detect the presence of an analyte. Therefore, it is a complex and time-consuming type of assay. Additionally, heterogeneous immunoassay is important for detecting high molecular weight analytes. Hence, the main difference between homogenous and heterogenous immunoassay is their type of steps.

References:

1. Homogenous enzyme immunoassay. Homogenous Enzyme Immunoassay – Creative Biolabs. (n.d.). 

Image Courtesy:

1. “Competitive homogeneous immunoassay” By NickCT – Own work (CC-BY SA 3.0) via Commons Wikimedia
2. “ELISA” By BiotechMichael – Own Work (Public Domain) via Commons Wikimedia