Fig. 6

Detection limit of ESAT-6 by the antibody-based colorimetric assay. a Graphical representation for the detection of ESAT-6. Different concentrations of ESAT-6 was mixed with 60 nM of antibody, and after 30 min of incubation, GNP was added. Then, 800 mM of NaCl was added to induce the color change. ESAT-6 protein was titrated from 1.25 pM to 5000 pM. Photographs were taken by the digital camera as in figure inset. b Spectral changes at the wavelength from 400 to 800 nm. Peaks were indicated with the respective colored spheres