The immune complex transfer enzyme immunoassay: Mechanism of improved sensitivity compared with conventional sandwich enzyme immunoassay.

Immune complex transfer enzyme immunoassay (ICT-EIA) is one of the technologies which enables ultrasensitive measurements of protein biomarkers. The ICT-EIA uses two types of beads and sandwich-shaped immune complexes are transferred from the 1st bead to the 2nd bead in the assay. The purpose of the study is to reveal the reason why the ICT-EIA achieves ultrasensitive measurements by making a detailed comparison between conventional sandwich enzyme immunoassay (Sand-EIA) and ICT-EIA. ICT-EIAs for cytokines were developed and the sensitivities were compared with the sandwich EIAs. ICT-EIAs had about 100 times higher sensitivities because of markedly decreased non-specific signals derived from non-specific binding of detection antibody conjugates onto the polystyrene bead. The results have enabled us to show the importance of reducing non-specific signals in EIAs to obtain higher sensitivities. This methodology should be more valuable if combined with a different label detection system such as digital counting or immuno-PCR, which may enable the detection of single target protein molecules in the near future.