Rapid and sensitive cardiac troponin I immunoassay based on fluorescent europium(III)-chelate-dyed nanoparticles.

Background: Cardiac troponins are the preferred and recommended biomarkers of myocardial infarction. Unfortunately, most of the current commercial assays do not meet the guideline recommendations for sensitivity and low-end precision. Therefore, improvements in their analytical performance are still needed.

Methods: Cardiac troponin I (cTnI) immunoassay was developed. The assay utilized a monoclonal antibody and a F(ab')(2) antibody fragment immobilized onto the microtiter wells for capturing, and a monoclonal antibody covalently conjugated to fluorescent europium(III)-chelate-dyed nanoparticles for detecting. Following a 15-min incubation of the sample and nanoparticle-bioconjugates in the capture wells, cTnI was quantified directly from the washed well surface by time-resolved fluorometry.

Results: The limits of detection and quantification were 0.0020 μg/l and 0.012 μg/l, respectively. The response was linear in the measured range of 0.003-9.6 μg/l. The within-run imprecisions were 9.8, 5.1, 7.7 and 5.4%, and the total imprecisions were 13.1, 10.4, 9.0 and 8.7% at cTnI levels of 0.007, 0.051, 0.52 and 2.62 μg/l, respectively. Plasma recoveries of added cTnI were 72-119%. Regression analysis with Innotrac Aio! 2nd generation cTnI assay yielded a slope (95% confidence intervals) of 1.197 (1.141 to 1.253) and y-intercept of 0.216 (-0.128 to 0.561)μg/l (S(yx) = 2.176 μg/l, n = 212, r = 0.945).

Conclusions: The developed immunoassay based on europium(III)-chelate-dyed nanoparticle label allows rapid and sensitive measurement of cTnI.