Chemiluminescence is the emission of light through a chemical reaction. It contrasts with fluorescence, which is excited by a light source. During chemiluminescence, the vibrationally excited product of an exoergic chemical reaction relaxes to its ground state with the emission of photons.[1] Since the process does not require excitation light, problems in its application caused by light scattering or source instability are absent, and there is no concern about autofluorescence in the background, which can lead to highly sensitive deep tissue imaging.[2]
Recently, many advances have been made in deep tissue optics regarding ultrasound modulated fluorescence and ultrasound switchable fluorescence. With its greater potential in medical imaging, ultrasound-enhanced chemiluminescence (UECL) has been developed as a second generation of chemiluminescence, and overcomes several limitations of chemiluminescence in deep tissue imaging.[3] The simultaneous use of ultrasound and chemiluminescence imaging techniques helps accurately visualize the tissue of interest in dual imaging. Additionally, ultrasound can serve as an efficient tool to enhance the intensity of chemiluminescence by reducing light scattering while increasing spatial resolution.[3]