LSBio Traditional ELISA Kits

LSBio offers over 20,000 cost-effective, ready-to-use ELISA kits for the quantitative or qualitative detection of thousands of targets of interest. Each kit includes all of the necessary reagents to perform the assay as well as a clear protocol that walks you through the entire process, from sample preparation to analysis of the results. LSBio’s ELISA kits use traditional Sandwich, Competitive EIA, and Direct assay formats. Sandwich ELISA kits are a fast and simple way to quantify specific target antigens in a variety of sample types including urine, plasma, and cell culture medium. Competitive EIA kits use a single, antigen specific capture antibody rather than paired antibodies, allowing for detection of molecules where no antibody pair exists. Direct ELISA kits focus on the detection of antibodies developed as part of an auto-immune response, as well as anti-viral or anti-bacterial antibodies.

There are several types of Sandwich ELISA assays, all of which start with an antigen-specific capture antibody bound to the plate. When a sample is applied, the target antigen binds to this capture antibody. The plate is then washed and the captured antigen detected. The specific detection system varies between assays but generally consists of a detection antibody directly or indirectly linked to HRP. Often Avidin-biotin complexes are used to amplify the amount of HRP. The HRP then modifies a chromogen substrate, such as TMB, producing a color that is detectable at a specific light wavelength.

Competitive EIA kits are a diverse group of assays, all of which are based upon competitive binding of the antibody or antigen. Unlabeled target antigen from the sample must compete for binding with a fixed amount of biotin- or HRP-conjugated target antigen supplied with the kit. The greater the amount of target antigen within the sample, the more it is able to out-compete the conjugated antigen. This causes a reduction in the detectable conjugated antigen. Unlike Sandwich or Direct ELISAs, the lower the detectable signal in a Competitive EIA assay, the greater the amount to target antigen in the sample.

Direct ELISA assays are ideal for the detection of antibodies in samples. There are two primary types of Direct assay, those that capture the target-specific antibody using the target antigen bound to the plate, or those that first capture all antibodies using a universal capture antibody bound to the plate, then detecting the captured target-specific antibody using the target antigen. Both assays employ a conjugated HRP which then modifies a chromogen substrate, such as TMB, producing a color that is detectable at a specific light wavelength.

Most ELISAs use 3,3',5,5'-tetramethylbenzidine (TMB) as their detection chromogen. When modified by Horseradish Peroxidase (HRP), TMB yields a blue color (370nm and 652nm) which then changes to yellow (450nm) upon the addition of a sulfuric acid stop solution. By running a dilution series of a known concentration standard, an OD450 standard curve can be generated. The OD450 for each unknown sample can then be compared to this standard curve in order to determine the concentration of target antigen.