Miniaturization of a homogeneous fluorescence immunoassay based on energy transfer using nanotiter plates as high-density sample carriers.
The miniaturization of a homogeneous competitive immunoassay to a final assay volume of 70 nL is described. As the sample carrier, disposable plastic nanotiter plates (NTP) with dimensions of 2 x 2 cm2 containing 25 x 25 wells, corresponding to approximately 15,000 wells on a traditional 96-well microtiter plate footprint, were used. Sample handling was accomplished by a piezoelectrically actuated micropipet. To reduce evaporation while pipetting the assays, the NTP was handled in a closed humid chamber and cooled to the point of condensation. To avoid washing steps, a homogeneous assay was developed that was based on energy-transfer (ET). As a model system, an antibody-based assay for the detection of the environmentally relevant compound, simazine, in drinking water was chosen. Antibodies were labeled with the long-wavelength-excitable sulfoindocyanine dye Cy5 (donor), and a tracer was synthesized by labeling BSA with a triazine derivative and the acceptor dye Cy5.5. At low analyte concentrations, the tracer was preferably bound to the antibody binding sites. As a result of the close proximity of Cy5.5 and Cy5, an efficient quenching of the Cy5 fluorescence occurred. Higher analyte concentrations led to a progressive binding of the analyte to the antibody binding sites. The increased Cy5 fluorescence was determined by using a scanning laser-induced fluorescence detector. The limit of detection (LOD), using an antibody concentration of 20 nM, was 0.32 microg/L, or 1.11 x 10(-16) mol of simazine. In comparison, the LOD of the 96-well microtiter-plate-based ET immunoassay (micro-ETIA) was 0.15 microg/L, or 1.87 x 10(-13) mol. The LOD of the optimized micro-ETIA at 1 nM IgG, was 0.01 microg/L.
Schobel
U
U
Institute of Physical and Theoretical Chemistry, Tübingen, Germany. u.schobel@virion-serion.de
Coille
I
I
Brecht
A
A
Steinwand
G M
GM
Gauglitz
G
G
D000911:Antibodies, Monoclonal / Q000378:metabolism; D001667:Binding, Competitive; D002138:Calibration; D005456:Fluorescent Dyes / Q000378:metabolism; D015200:Fluoroimmunoassay / Q000295:instrumentation* / Q000379:methods*; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods; D036103:Nanotechnology / Q000295:instrumentation / Q000379:methods; D014881:Water Supply / Q000032:analysis
D000911:Antibodies, Monoclonal; D005456:Fluorescent Dyes