Development of a low density colorimetric protein array for cardiac troponin I detection

This work presented a rapid, inexpensive, reliable, and flexible quantitative immunoassay for cardiac troponin I (cTnI). The assay was based on the concepts of one-step dual monoclonal antibody "sandwich" principle, the low density protein array, the nanogold probe, and the silver enhancement on the gold particles. The capture antibody (IgG1) coated supporting nitrocellulose membrane and the colloidal gold-labeled detection antibody (cAu-IgG2) were prepared before the detection. The detection procedure involved two steps, i.e., immunoreaction and silver amplification. The assay needs only small amounts of serum samples of patients, The whole detection procedure of the assay could be fulfilled within 40 min (much faster than the routine enzyme-linked immunosorbent assay (ELISA) that takes usually at least 3 hours for a turnaround test). The detection results could be easily imaged with a simple flatbed scanner or even observed with the naked eye. The assay showed good specific response to cTnI with very little cross-reactivity to the skeletal isoforms of troponin I (sTnl), cardiac troponin T (cTnT), and myoglobin (Mb). A cut-off value of 0.3 ng/ml was obtained from a reference control group (200 normal serum samples). 588 patients' serum samples were assayed simultaneously by routine ELISA and this colloidal gold method to test the validity of the method. The data were analyzed using the statistical package SPSS version 11.0 (SPSS Inc.) There was no significant difference between these two assays (P = 0.66 > 0.05). The agreement between this method (> or < 0.3 ng/ml) and ELISA was 86%.