Absorbing molecules as optical clearing agents improve the resolution and sensitivity of photoacoustic microscopy

Photoacoustic microscopy (PAM) offers high resolution and 100% sensitivity to optical absorption, making it promising for biomedicine. However, strong light scattering in tissues limits its imaging depth, intensity, and resolution. Optical clearing agents (OCA) can reduce light scattering. However, traditional methods often use toxic substances or damage tissue components, restricting their application in living tissues. Recently, tartrazine, a common food pigment, has been shown to significantly improve tissue optical transparency while maintaining good biosafety. However, it is unclear whether tartrazine as an absorbing molecule is suitable for use in PAM. In this study, we show that tartrazine, despite its strong light absorption, can significantly enhance the performance of PAM, when used at an appropriate concentration. Our ex vivo experiments demonstrate tartrazine solution enables PAM to achieve an optical resolution of 21 μm even through the skin. A 0.6 M tartrazine solution improves resolution by 3.5 times and the imaging intensity by 4.5 times. Finally, in vivo brain imaging of a mouse with an intact scalp reveals that tartrazine not only increases the imaging intensity by about 4 times but also allows PAM to achieve an optical resolution of brain through the scalp and skull, revealing much more details of the microvasculature in the brain.