A terahertz chemical microscope to visualize chemical concentrations in microfluidic chips

Here, a new type of terahertz chemical microscope (TCM) is proposed and developed, and the first demonstration of imaging the chemical concentration in fluid channels is reported. Fluid samples flow through channels possessing a semiconductor sensing plate as a bottom wall. Terahertz (THz) waves are radiated from the sensing plate as a result of femtosecond laser illumination. Because the amplitude of the THz radiation depends on the concentration of ions adsorbed on the surface of the plate, the ion distribution in the fluid channels can be visualized by scanning the laser across the plate. An image showing separated solutions with two different proton concentrations is successfully observed as the first demonstration of this instrument.