A rapid, inexpensive, reliable, and flexible quantitative immunoassay for cardiac troponin I (cTnI) 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 particle were provided. The whole detection procedure of the assay could be fulfilled within 40 min with the pretreated colloidal gold-labeled detection antibody and supporting substrate. The assay showed good specific response to cTnI with very low cross-reactivity ratio to the skeletal isoforms of troponin I (sTnI), cardiac troponin T (cTnT), and myoglobin. 588 serum samples were assayed simultaneously by enzyme-linked immuno sorbent assay (ELISA) and this colloidal gold method to test the validity of the method and 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 ngmL) and ELISA was 86%. A rapid, inexpensive, reliable, and flexible quantitative immunoassay for cardiac troponin I (cTnI) 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 The whole detection procedure of the assay could be fulfilled within 40 min with the pretreated colloidal gold-labeled detection antibody and supporting substrate. The assay showed good specific response to cTnI with very low cross-reactivity ratio to the skeletal isoforms of troponin I (sTnI), cardiac troponin T (cTnT), and myoglobin. 588 serum samples were assayed simultaneously by enzyme-linked immuno sorbent assay (ELISA) and this colloidal gold method to test the validity of the method and the data 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%.