The enzyme-linked immunosorbent assay (ELISA), sometimes referred to as enzyme immunoassay (EIA), is a popular, simple, and cost-effect detection technique. It uses enzymes and antibodies or antigens to identify a substance in a liquid sample, such as serum/plasma, culture supernatant, and cell/tissue lysate. ELISA is a wet lab type analytic method, which is opposed to the dry lab analytic method that can use dry strips.
ELISA is a plate-based assay technique: it involves the use of a solid surface, usually a polystyrene multiwell plate, which distinguishes ELISA from other antibody-based assays. In ELISA, the analyte (the substance analyzed) in a sample is immobilized on the solid surface, while other components in the sample will be removed by a detergent solution. In this way, the solid surface enables the separation of the analyte from the sample. After the analyte is immobilized, the detection antibody linked to an enzyme is added, forming an antigen-antibody complex. Finally, an enzymatic substrate is added to react with the enzyme. The enzymatic reaction generates a visible signal, usually color change, that can be measured.
Given its convenience and effectiveness, ELISA has wide applications in disease diagnosis, biomedical research, and various industries. Virtually any type of molecule (protein, lipid, carbohydrate, nucleic acid, etc.) can be detected by the method of ELISA. Using ELISA to determinate serum antibody/antigen concentrations helps diagnose infectious diseases caused by viruses, bacteria, and other pathogens. There are commercially available ELISA kits for the diagnosis of HIV/AIDS, flu, common cold, cholera, WNV, TB, hepatitis B, and many other infectious diseases in humans and animals. ELISA is also used as a diagnostic tool in plant pathology. Besides, ELISA is applied to vaccine development, drug screening, and home pregnancy test. In the food industry, ELISA is a useful tool to ensure the safety and quality of food as it can detect harmful substances in food, such as allergens.
When you need an ELISA kit to analyze a sample, how can you choose a right one from so many commercially available ELISA kits There are many types of ELISA, such as direct, indirect, sandwich, and competitive. Most suppliers offer 96T ELISA kits, and some suppliers like CUSABIO offers 24T trial ELISA kits. In addition to ELISA types and packaging specifications, there are other important factors that you should take into consideration when you are choosing an ELISA kit. Here are 11 tips for choosing the right ELISA kit for your samples.
1. The species studied
If the sample is from a classical model such as human, mouse, and rat, it is relatively easy to find a validated ELISA kit. But if the sample is from a non-classical model such as monkey, there are limited numbers of commercial ELISA kits available. In this case, you may have to choose a kit validated on species that shows homology with the species of your sample.
2. The analyte detected
You should clearly understand what kind of analyte (usually protein) to detect. A sandwich ELISA is generally suitable for detecting large proteins with multiple epitopes such as a cytokine. A competitive ELISA is appropriate for detecting small molecules like hapten.
Most commercial ELISA kits are validated on serum/plasma and culture supernatants. It is important to read the product instructions in detail to ensure that the kit is compatible with your sample. For example, the way that plasma samples are collected (heparin or EDTA) can affect which ELISA kit should be chosen. Besides, other factors such as hemolysis and the presence of lipids in the sample can interfere with assay performance. So take these factors into consideration before choosing an ELISA kit. Purchasing a trial size ELISA kit to do a pre-test with your samples is recommended to verify whether the kit is suitable and sensitive to the sample.
3. Purpose of the analysis
ELISA is a tool that can be used for both qualitative and quantitative analyses. Qualitative ELISA provides a simple positive or negative result for a sample, while quantitative ELISA reflects the concentration of the analyte in a sample via a standard curve. Do you want to quantify the analyte in your sample or only to detect the presence/absence of it Based on the purpose of the analysis, you can choose between qualitative ELISA and quantitative ELISA.
4. Type of antibodies
You can consult the ELISA kit suppliers what types of antibodies are used in the kit: monoclonal or polyclonal antibody In sandwich ELISA, it is sometimes helpful to use a polyclonal antibody for capture and a monoclonal antibody for detection.
5. Requirement of sensitivity
If you don't have a clue about the concentration of the analyte in your sample, ELISA kits with a broad detection range are a better choice. If the concentration of the analyte in the sample is very low, ELISA kits with high sensitivity are recommended. If the concentration of the analyte is too high, dilution of samples may be made to adapt to the detection range of the ELISA kit.
6. Sample size
ELISA kits usually require from 100ul down to 10ul sample. If the amount of your sample is very small or your sample is very precious, you'd better choose ELISA kits that require less amount of sample.
7. Recovery and linearity data
Recovery and linearity experiments are used to assess the performance of ELISA kits. Recovery helps determine whether analyte detection is affected by differences in sample matrices. High recovery is better. The linearity of dilution determines the extent to which the dose-response of the analyte is linear in a particular diluent. Ideally, the concentration of the samples should be similar for all dilutions.
Most suppliers provide recovery and linearity data on product specifications. Besides, other important parameters such as sensitivity and dynamic range are also provided. ELISA kits of different manufacturers may have different parameter data. You can carefully compare these parameter data, particularly recovery and linearity data, to choose a right ELISA kit.
8. Detection system
There are several different detection systems in ELISA, including colorimetric, fluorescent, and luminescent methods. All ELISA involves the immobilization of the analyte to a surface as well as the use of an enzyme label and a matching substrate. Choosing an appropriate enzyme and a matching substrate is important. Moreover, enzyme-substrate reaction conditions, the microplate, and the detection device should be properly chosen.
9. The experimental protocol
ELISA kits with simple protocols, convenient operation, and short experiment time will make it easier for you to do an ELISA test.
ELISA kits that have been used by other researchers and reported in the literature are typically more trustworthy. Additionally, manufacturers and products that have received certification are generally more reliable. See more than 3158 literatures from CUSABIO.
The price is always a factor for selection, particularly when the budget is limited. ELISA kits are usually 96T. Shipping cost should also be taken into consideration.
To conclude, you can refer to these criteria to choose ELISA kits that are suitable for your applications. If you still need additional technical support, feel free to contact CUSABIO, which is specialized in the manufacture of ELISA kits and other products. As many as 3158 published papers have involved CUSABIO ELISA kits. Recently, CUSABIO started the ELISA kit promotion, which is available from 8/1/2017-9/30/2017. You can apply for a 24T trial size of all CUSABIO ELISA kits except food safety ELISA kits on this page: http://www.cusabio.com/24T_ELISA/