Biorecognition and detection of antigens from Mycobacterium tuberculosis using a sandwich ELISA associated with magnetic nanoparticles

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is one of the 10 leading causes of death worldwide, especially in low-income areas. A rapid, low-cost diagnostic assay for TB with high sensitivity and specificity is not currently available. Bio-functionalized magnetic nanoparticles (MNPs) which are able to efficiently detect and concentrate biomolecules from complex biological samples, allows improving the diagnostic immunoassays. In this way, a proof-of-concept of MNP-based sandwich immunoassay was developed to detect various MTB protein antigens. The superficial and secretory antigenic proteins considered in this research were: CFP10, ESAT6, MTC28, MPT64, 38 kDa protein, Ag85B, and MoeX. The proteins were cloned and expressed in an E. coli system. Polyclonal antibodies (ab) against the recombinant antigens were elicited in rabbits and mice. Antibodies were immobilized on the surface of amine-silanized nanoparticles (MNP@Si). The functionalized MNP@Si@ab were tested in a colorimetric sandwich enzyme-linked immunosorbent assay (sELISA-MNP@Si@ab) to recognize the selected antigens in sputum samples. The selected MTB antigens were successfully detected in sputum from TB patients in a shorter time (~ 4 h) using the sELISA-MNP@Si@ab, compared to the conventional sELISA (~15 h) standardized in home. Moreover, the sELISA-MNP@Si@ab showed the higher sensitivity in the real biological samples from infected patients.