A label-free electrochemical immunosensor based on an ionic organic molecule and chitosan-stabilized gold nanoparticles for the detection of cardiac troponin T.

A label-free electrochemical immunosensor based on an ionic organic molecule ((E)-4-[(4-decyloxyphenyl)diazenyl]-1-methylpyridinium iodide) and chitosan-stabilized gold nanoparticles (CTS-AuNPs) was developed for the detection of cardiac troponin T (cTnT). The new ionic organic molecule was strategically employed as a redox probe, and CTS-AuNPs were applied as a "green" platform for the immobilization of the monoclonal anti-cTnT antibody, for the construction of the immunosensor. The characterization of the proposed immunosensor was carried out by employing cyclic and square-wave voltammetry and electron microscopy. The film of ionic organic molecules acts as a redox probe and from its electrochemical response the presence of cTnT antigens, which interact specifically with the anti-cTnT antibody immobilized on the surface of the immunosensor, can be detected. This interaction results in a decrease in the analytical signal, which is proportional to the amount of cTnT antigens present in the sample analyzed. Under optimized conditions, using square-wave voltammetry (a frequency of 100 Hz, an amplitude of 100 mV and an increment of 8 mV) and an incubation time of 10 min, the proposed immunosensor showed linearity in the range of 0.20 to 1.00 ng mL(-1) cTnT, with a calculated limit of detection of 0.10 ng mL(-1). The proposed immunosensor shows some advantages when compared to other sensors reported in the literature, especially with regard to the detection limit and the time of incubation. A study of the interday precision (n = 8) showed a coefficient of variation of 3.33%. The potential interference of some compounds (glucose, ascorbic acid, albumin, uric acid, creatine, and creatinine) on the response of the immunosensor was evaluated and the inhibition of the immunosensor response was found to be less than 8.0%. The immunosensor was successfully used for the determination of cTnT in samples of simulated blood serum with a relative error of <13.0%. Furthermore, the proposed methodology provides a working range that allows the detection of cTnT antigens at levels below the cutoff value used for the diagnosis of acute myocardial infarction and was also found to be faster than the conventional methods.