For Researchers, using techniques like flow cytometry, Western Blotting, ELISA and immunohistochemistry, antibodies are used to quantify antigens in complex biological samples. These days, it is possible to measure hundreds of antigens simultaneously with multiplex immunoassay technologies. Generally all of these antibody-based detection techniques require a label (antibody labelling) of some description which allows measurability.
The vast majority of antibodies that are available commercially are not labelled, which means they are not quantifiable. Generally only a small number of antibodies, those deemed commercially valuable by the antibody manufacturers, are available in conjugated/labelled form. Also, for the antibodies that are available in conjugated form, it is generally for a small range labels. This can be very restricting when it comes to experimental design.
Using unlabeled antibodies comes with several inherent problems particularly with multiplex assays. For Indirect detection, which commonly uses a secondary antibody with the required label, it is difficult to create a panel of secondary reagents with the desired selectivity and lack of unwanted cross reactions. These problems are overcome, however, by covalently attaching the label directly to the primary antibody, reducing the complexity of immunoassays and quickly and simply producing a flow cytometry antibody ready for analysis.
Historically, antibody labelling has involved chemical modification and has been conducted by commercial organisations with specialist knowledge of the required techniques. However, due to significant advances in antibody labeling technologies, this once difficult, time consuming and costly procedure can now be performed by anyone in the lab without the need for specialist training or experience.