Label-free detection of proteins using a terahertz chemical microscopy

A terahertz chemical microscopy (TCM) has been proposed and developed to visualize the distribution of chemical reactions such as antigen-antibody reaction on the sensing plate without any labels on the analyte. The TCM utilize the semiconductor-based device named a sensing plate. The sensing plate can convert the shift of the chemical potential in the magnitude on the surface of sensing plate into the amplitude of generated terahertz (THz) in the sensing plate. Thus, it enables to get images of the potential distribution on the surface of the sensing plate as the distribution of THz amplitude. Here, we demonstrate the detection of the immune reactions between the mouse immunoglobulin G (IgG) and the anti-mouse immunoglobulin G (anti-IgG). IgG was immobilized on the sensing plate and reacted with anti-IgG in the solutions with various concentrations. We also fabricated the sample wells on the sensing plate and quantitative evaluation of immune reactions were demonstrated with the anti-IgG concentration of between 5 nM and 100 nM. As a result, the change in the THz amplitude during the reaction showed the proportional relation with the concentration of reacted anti-IgG.