A terahertz chemical microscope (TCM) has been proposed and developed to visualize the distribution of the antibody-antigen bindings on the silicon based sensing plate without any labels and/or markers on the antibody. The sensing plate can emit the terahertz pulses by femtosecond laser pulses and the amplitude of the terahertz pulses can be related to the chemical or electric potential of the sensing plate surface at where the laser pulses are irradiated. Thus the potential distribution can be visualized as the map of the terahertz pulses amplitude.As the first demonstration of the label free immune assay, the mouse immunoglobulin G (IgG) was immobilized on the half part of the sensing plate and the mouse anti-IgG was combined with the IgG. The terahertz pulses were enhanced at where anti-IgG was combined with IgG on the sensing plate and the distributions of the IgG and anti-IgG bindings on the sensing plate were clearly seen as the TCM images. The amplitude of terahertz pulses as a function of the concentration of anti-IgG was also investigated. (C) 2012 Elsevier B. V. All rights reserved.