Immunoassay kits and assay technologies

Immunoassay technology typically uses antibodies to detect specific target analytes. Although immunoassays have been around for decades, advances in this field are transforming how we treat and monitor diseases from cancer and infectious illnesses to autoimmune disorders. A whole range of immunoassay techniques are available. These techniques can be distinguished by their detection method, like colorimetry, fluorescence, or turbidimetry.

ELISA (enzyme-linked immunosorbent assays) is by far the most implemented, lab-based immunodiagnostic method. It is the foundation on which many alternative immunoassays have been developed. From screening for infectious diseases such as HIV and hepatitis to assessing cardiac biomarkers indicative of myocardial infarction, ELISA plays a crucial role across disease detection and medical care.

The four main types of ELISA are direct ELISA, indirect ELISA, sandwich ELISA, and competitive ELISA.

• Direct ELISA: This method involves immobilizing the antigen directly onto a solid surface, such as a microtiter plate. A conjugated detection antibody (labeled antibody) that recognizes the antigen is added, and the signal generated is proportional to the amount of antigen present.
• Indirect ELISA: Like the direct method, this method starts by immobilizing the antigen on a solid surface. Then, an unlabeled primary antibody binds to the antigen. A secondary antibody, which is labeled, binds to the primary antibody. This method amplifies the signal and is often used for increased sensitivity.
• Sandwich ELISA: In this method, a capture antibody is immobilized onto a solid surface, the sample is added, and then a detection labelled antibody is added. If an antigen is present in the sample, the capture antibody and detection antibody binds to the opposite end of the same target antigen, forming a sandwich and is detected.
• Competitive ELISA: This method is used for quantifying the amount of an analyte in a sample. It works by using a fixed amount of labeled antigen that competes with the sample antigen for binding to a limited number of antibodies.

One of its biggest drawbacks of ELISA is its susceptibility to nonspecific binding, which can lead to a high background signal that compromises assay specificity and accuracy. Additionally, the antigen-antibody reaction requires a long incubation period, with diagnostic results generally provided in 4 to 6 hours.

Chemiluminescent immunoassays (CLIAs) are highly sensitive and versatile alternatives to ELISA. Like ELISA, they are lab-based and use antibodies to detect analytes. Opting for a luminescent signal makes CLIAs less susceptible to background interference. The enhanced signal-to-noise ratio boosts assay specificity. CLIAs can also detect analytes at trace-level concentrations, which is particularly advantageous for identifying biomarkers associated with early-stage diseases or monitoring disease progression. Additionally, CLIAs offer rapid assay kinetics, reducing incubation times and accelerating time-to-result compared to ELISA.

Enzyme-linked immunosorbent assays (ELISAs):

• Pros: Staple technique, popular for its simplicity, sensitivity, and specificity.
• Cons: Nonspecific binding can lead to high background noise. The typical turnaround time is 4 to 6 hours.

Chemiluminescent Assays (CLIAs):

• Pros: Overcomes some limitations of traditional ELISA, offering heightened sensitivity.
• Cons: Can be susceptible to interference from other substances present in the sample such as biotin and hemoglobin.

Fluorescence immunoassays (FIAs):

• Pros: Reduced background interference and high sensitivity. Can simultaneously detect multiple biomarkers from a single sample.
• Cons: Photobleaching effect can occur, where fluorescent dyes degrade upon exposure to light, reducing signal intensity and impacting results.

Turbidimetric immunoassays:

• Pros: Quick turnaround times and minimal sample preparation requirements.
• Cons: Low sensitivity, which can be problematic when detecting trace levels of target analyte.

Magnetic beads, or magbeads, are a type of nanotechnology that can address many challenges associated with conventional immunoassays like ELISAs and CLIAs. Magbeads are particles of iron oxides that give them superparamagnetic properties. Magbeads can be engineered with variety of surface chemistry options. Custom ligands can even be conjugated onto the beads’ surface. They can be used for several purposes in immunodiagnostics, including as biomolecule carriers, reaction support phases, and separation tools. To streamline immunoassays, magbeads can be coated with specific antibodies or antigens that bind to the target analyte. A magnetic field is then applied to separate the magbead bound complexes from the rest of the sample; an effective process that reduces background noise and enhances assay sensitivity.