Evaluating tartrazine as an optical clearing agent for fluorescence lifetime imaging

Fluorescence lifetime imaging (FLI) offers valuable insights into the molecular and functional properties of biological tissues. However, in deeper tissues, optical properties (scattering and absorption) diminish fluorescence signal significantly and complicate data interpretation. This study explores the potential of tartrazine (FD&C Yellow 5), a biocompatible and FDA-approved food dye, as an optical clearing agent for deep tissue imaging. Despite its own near-infrared (NIR) fluorescence, tartrazine's ultrashort intrinsic lifetime (∼0.10 ns) allows for effective separation from the longer lifetimes of conventional NIR probes (>0.50 ns) using lifetime-based unmixing. We found that at an optimal concentration (≤ 0.6 M), tartrazine brings down the reduced scattering coefficient (μs') by more than 90%, significantly improving fluorescence signal recovery from deeper tissue regions. Our validation with multi-depth tissue phantoms showed that this method can accurately recover fluorescence signals and lifetimes from targets located more than 1 cm deep, achieving results comparable to low-scattering controls. These findings show that tartrazine is a practical and effective optical clearing agent that can enhance the depth, resolution, and quantitative accuracy of FLI in highly scattering media, such as those used in preclinical imaging studies.