Cardiac Troponin I Determination by an ELISA on Magnetic Particles with Electrochemical Detection

A highly sensitive method for the quantitative rapid determination of cardiac troponin I (cTnI) in human serum is developed. The method is based on an enzyme-linked immunosorbent assay (ELISA) on magnetic particles in the volume of a blood serum sample, which can significantly reduce the diffusion limitations typical for the traditional ELISA. Alkaline phosphatase which is a high-performance enzyme was used as an enzyme label. The enzyme demonstrated a catalytic efficiency of (k_cat/K_m) = 26 500 L/(s mM) in combination with the substrate 1-naphtyl phosphate monosodium salt. The planar electrochemical sensors manufactured by industrial screen-printing technology are used for signal detection. The detection is carried out in differential pulse voltammetry mode. The calculated limit of detection by the enzymatic reaction product is 0.075 μM which significantly exceeds the sensitivity of colorimetric methods. The combination of the proposed methods and approaches makes it possible to obtain a quantitative analysis for cTnI in human serum within 20 min with an estimated detection limit of 7 pg/mL and the upper reference limit of the normal analyte concentration (99th percentile) of 22 pg/mL.