Facile and sensitive method for detecting cardiac markers using ubiquitous pH meters.

A sensitive and easy method was developed for the detection of the cardiac marker troponin I using magnetic immunoassay and ubiquitous pH meters. Monoclonal antibody-functionalized Fe3O4 magnetic nanoparticle clusters (MNCs) were synthesized to capture troponin in human serum, and MNC-troponin complexes were magnetically isolated using a permanent magnet. These complexes were subsequently conjugated to polyclonal antibody-functionalized acetylcholinesterase (AchE) and dispersed in acetylcholine (Ach) solution. As the Ach was hydrolyzed to choline and acetic acid, the pH of the solution decreased, and the resulting pH change was measured in real time using a pH meter. The sensitivity of detection of this assay was found to be 10 pg/mL of troponin in human serum after 10 min of the hydrolysis reaction. Further, the pH change could be determined with the naked eye from the color change of a pH indicator strip.