pH Readout enhanced ELISA for point-of-care testing of cardiac troponin I

Enzyme-linked immunosorbent assay (ELISA) as a conventional method for protein quantification has its characteristic properties, however, it is challenging to implement excellent portability and sensitivity at the same time. In this study, we described a pH ELISA using synthetic melanin nanoparticles (SMNPs) for the co-immobilization of glucose oxidase (GOx) and second antibody (Ab2) as signal labels, portable pH meter as signal readout device for point-of-care testing (POCT) of cardiac troponin I (cTnI). In accordance with the varying amount of cTnI, following sandwich type immunoassay, proportional SMNPs-GOx-Ab₂ were immobilized specifically resulting in corresponding decrease of pH values owing to GOx loaded on SMNPs can high-efficiency convert glucose into gluconic acid. This assay is easy-to-use, portable, sensitive and able to realize POCT, affording a linear range from 0.5 pg/mL to 10 ng/mL and low limit of detection (LOD) of 0.15 pg/mL towards cTnI, which was demonstrated the significant promising in the early diagnosis and screening of acute myocardial infarction.