Method Description

Chromogranin A (CgA) is measured in a homogeneous automated immunofluorescent assay. This assay uses technology based on a variant of Forster resonance energy transfer, called time-resolved amplified cryptate emission (TRACE). A mouse monoclonal antibody against CgA is labeled with europium cryptate (TRACE donor) and a second mouse monoclonal antibody against CgA is labeled with Alexa Fluor 647 (TRACE acceptor). CgA is sandwiched between the 2 antibodies, bringing them into close proximity. When the antigen-antibody complex is excited with a nitrogen laser at 337 nm, some fluorescent energy is emitted at 620 nm, and the rest is transferred by nonradiative dipole-dipole coupling to Alexa Fluor 647. This energy is then emitted as fluorescence at 647 nm. A ratio of the energy emitted at 647 nm to that emitted at 620 nm (internal reference) is calculated for each sample. Signal intensity is proportional to the number of antigen-antibody complexes formed and, therefore, to antigen concentration.(Package insert: B R A H M S CgAII KRYPTOR Instruction for Use. Thermo Fisher Scientific Inc; V1.1us, 09/2023)