Sandwich ELISA Kits

Enzyme-linked immunosorbent assays (ELISAs) are microplate based methods for detecting analytes of interest in solution. They offer the advantages of high specificity and sensitivity, ease of use, and the capacity to provide quantitative data. In addition, ELISAs are extremely flexible, allowing for the analysis of a range of sample types including cell lysates, culture supernatants, and tissue homogenates, as well as serum, urine, and saliva. Applications for ELISAs span basic research through to clinical testing. ELISAs are broadly divided into four main groups — direct ELISAs, indirect ELISAs, sandwich ELISAs, and competitive ELISAs — depending on how they are configured. Of these, sandwich ELISAs are more widely used than direct and indirect ELISAs due to their superior specificity. During a sandwich ELISA, the microplate wells are coated with an analyte-specific antibody, then the samples are added. After incubation to allow for analyte capture, the microplate is washed to remove any unbound material. Next, a second analyte-specific antibody is introduced into the microplate wells. Critically, this must recognize a different epitope from that which is recognized by the capture antibody to avoid competition for analyte binding. Lastly, after further washing, the bound analyte is detected. Detection can involve one of several approaches. Often, the second analyte-specific antibody is labeled with an enzyme such as horseradish peroxidase (HRP) or alkaline phosphatase (AP), which is paired with an appropriate chromogenic or chemiluminescent substrate to produce a measurable signal. Alternatively, the second analyte-specific antibody may be biotinylated and a streptavidin conjugate (e.g., streptavidin-HRP) used for detection. Another method involves using a labeled secondary antibody for indirect detection of the second analyte-specific antibody. However, this is less common as it adds an extra step into the assay workflow and can also introduce the potential for non-specific cross-reactivities (e.g., secondary antibody binding to the capture antibody or the analyte). The interpretation of ELISA data requires the use of positive and negative control samples, as well as a calibration standard against which the concentration of the test samples can be calculated. While it is possible to develop an ELISA in-house, using antibodies validated for ELISA or matched antibody pairs, many researchers prefer to use pre-formulated kits, which can save both time and money. Off-the-shelf sandwich ELISAs typically include calibration standards and/or controls, along with details of the assay detection range and sensitivity. Many of our ELISA kits are also supplied in a strip format to enable you to run partial plates if required. Explore our range of sandwich ELISA kits below and discover more, for less.