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

Abstract 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.