Tartrazine-enabled optical clearing for in vivo optical resolution photoacoustic microscopy

Optical-resolution photoacoustic microscopy (OR-PAM) is a powerful imaging technique that visualizes microvascular and tissue structures with high spatial resolution, offering valuable insights into physiological and pathological processes. However, strong optical scattering in biological tissues fundamentally limits its imaging depth. Recent studies have suggested that tartrazine, a food-grade water-soluble dye, may serve as an effective optical clearing agent (OCA), yet its strong optical absorption near 532 nm raises concerns about compatibility with green-light-based OR-PAM systems. In this study, we demonstrate that by carefully controlling the concentration of tartrazine, it can effectively function as an OCA for OR-PAM at 532 nm without compromising signal quality. In vivo experiments on mouse ear and abdominal tissue showed that tartrazine significantly enhanced microvascular visibility across all tested concentrations, with the 15% weight of solute per weight of solution providing optimal clearing performance. Additionally, we evaluated 4-aminoantipyrine as another dye-based OCA, which also improved image clarity, albeit to a lesser extent. These findings highlight the promise of absorbing dye-based OCAs like tartrazine in enhancing in vivo OR-PAM by mitigating light scattering, potentially enabling deeper and clearer photoacoustic imaging in biomedical applications.