DELFIA dissociation-enhanced lanthanide

The DELFIA assay, the first effective lanthanide-based immunoassay, was developed and commercialized by the early 1980s.108-112 DELFIA (Dissociation Enhanced Lanthanide Fluoro-ImmunoAssay) is a heterogeneous assay which uses a lanthanide complex based on aminocarboxylate ligands such as EDTA, EGTA, or DTPA, linked to the antibody by reaction of appended isothiocyanate groups (e.g., complex (45)) with nucleophilic residues, particularly amines, on the protein surface (Figure 11). 

Fig. 25. (A) DELFIA (Dissociation Enhanced Lanthanide Fluoro-ImmunoAssay) system. This heterogeneous immunoassay system uses a primary antibody bound to a solid support, to which a variable amount of unlabeled antigen is bound. The secondary antibody is labeled with a non-phospho-rescent lanthanide chelate, which becomes phosphorescent after dissociation from the antibody, due to the addition of an enhancement solution [which typically contains a mixture of sensitizer (typically a (1-diketonate) and micelle inducing surfactant (5). (B) Heterogeneous fluoroimmunoassay using a secondary antibody directly labeled with a phosphorescent lanthanide chelate.

DELFIA Dissociation-Enhanced Lanthanide I/O Input/Output... 

Pro-inflammatory cytokines are important mediators of inflammation and tissue destruction. This section describes two cell-based assays that were used to screen for inhibitors of cytokine production and some of the compounds discovered using these screens. The two screens were important elements of a collaboration between Xenova Ltd and the Suntory Institute of Biomedical Research to find microbial metabolites with potential utility for the treatment of rheumatoid arthritis. Both screens were cell stimulatory assays with similar formats, the principle of which is illustrated in Figure 3. Treatment of cells with a particular stimulus activates a signal transduction pathway, one of the end results of which is production of a cytokine, which is secreted into the assay medium. After a separation step, the cytokine of interest is measured quantitatively in the supernatant by dissociation enhanced lanthanide fluorescence immunoassay (DELFIA) using a europium-labeled tertiary antibody. At the same time, cytotoxic properties of test substances are determined by assessing their effect on proliferation of the separated cells. 

Schoket B, Doty WA, Vincze I, et al. 1993. Increased sensitivity for determination of polycyclic aromatic hydrocarbon-DNA adducts in human DNA samples by dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA). Cancer Epidemiology, Biomarkers Prevention 2 349- 353. 

The dissociation-enhanced lanthanide fhtoroimmunoassay (DELFIA) technique is based on the principle of TRF. This theoretical concept was reduced to practice in the early 1970s [1 3] and was subsequently commercialized by the scientific equipment manufacturer, LKB/Wallac, as time-resolved fluorometric immunoassay methodology in the early 1980s [4 6]. DELFIA represents the first ultrasensitive nonisotopic immunoassay. This technology was reviewed in detail by Soini and Lovgren [7]. 

Several different assay formats, as already mentioned earlier, can generally be used such as ELISA, fluoroimmunoassay (FIA), dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA), RIA, and SPR. For the quantification of proteins in biological matrices such as blood, plasma, serum or urine, most often FLISAs are validated. 

Different variations of time-resolved luminescence assays were patented in 1982 by Wieder [1], in 1983 by Soini and HemmUa [2], and in 1999 by Diamandis [3]. The Finnish company Wallac first commercialized the principle and introduced an assay reader for dissociation-enhanced lanthanide fluorescence immunoassay (DELFIA) in the beginning of the 1980s. The first (1982) DELFIA-based bioassay for diagnostic market was for Rubella antibodies, and it was the first sensitive nonradioisotope innnunoassay marking the beginning of a new era [4]. 

With the DELFIA chelates, the sensitivity is, furthermore, increased because of the dissociation-enhancement principle the lanthanide ion in the chelate is dissociated and a new highly fluorescent chelate is formed inside a protective micelle (Figure 2). 

In the DELFIA type of chelate the labelled protein as such is practically non-fluorescent. After the immunoreactions, however, europium or samarium is efficiently dissociated from the labelled compound within a few minutes by the low pH of the enhancement solution. Free lanthanide ions rapidly form a new and highly fluorescent chelate inside a protective micelle with the components of the... 

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