Every assay can be adversely affected by interfering substances, but these are typically easy to overcome. The best way to do this is to use a protein standard that produces a similar colour response curve to the tested sample and can be easily obtained by any laboratory at any time. Here are some different types of assays:
Immunoassays
Immunoassays are an important tool in industry and the life sciences, and they’re largely responsible for better disease treatments, safer food and water and advances in biological research. They determine the presence and concentration of micro- or macro molecule chemicals in a solution using antibody-antigen reactions. Antibodies are Y-shaped proteins produced by human and animal immune functions that react to unknown substances (antigens) like viruses, bacteria and toxins. Antibodies bind to specific antigens, locking onto them like a lock and key.
Ligand-Binding Assays
There are several labelled and label-free methods to investigate the binding of ligands to receptors. For example, SPR and PWR use light-excited surface plasmon polaritons to track the change in the amplitude, position and width of reflected lights due to binding-induced conformational changes of a receptor molecule. Thermodynamic and structure-based methods also have been developed.
Fluorescence spectroscopy (FA) utilizes fluorophores that emit unequal amounts of light at different axes of polarization. Various techniques, including fluorescence anisotropy, fluorescence correlation spectroscopy and time-resolved measurements, have been used for FA assays.
Rapid/Simple Single Use
These assays are based on particle agglutination assays but use disposable, single-use biosensors rather than glass microtiter plates. They provide a simple qualitative result within minutes. However, they are dependent on subjective evaluation and no permanent record of the original test results can be kept. They are also limited in their ability to detect neutralizing antibodies (NAbs).
Using biolayer interferometry, BLI-ISA measures the presence of antigen-specific antibodies in plasma and provides real-time data output that aligns with signals in a dilution series ELISA, making it semi-quantitative. BLI-ISA is also simple to perform, as the samples are simply pipetted into a 96 or 384-well plate and loaded into the instrument with single-use biosensors.
Cell-Based Assays
Choosing the right cell-based assay depends on what information you want to measure. Choosing the appropriate assay format for each stage of drug development is important, as well as having a clear understanding of the context of use for that assay.
Cell-based assays offer a more complex representation of a drug in a real life model and can help accelerate drug discovery programs to clinical trials by providing data in the most relevant biological environment. Cell-based assays may measure a number of cellular activities including cell viability, cytotoxicity or apoptosis.
