Pyrene-fused dioxaborine-based merocyanines with high brightness, photostability, and fluorogenic function for deep-skin tissue imaging of a living mouse

Abstract

Abstract Bright polymethine dyes, typified by carbocyanines, are employed in various fluorescence techniques such as the 3D visualization of living cell morphology and the tracking of extracellular vesicles in the blood vessels of a zebrafish. However, they often exhibit low photostability, particularly for dyes with red-shifted absorption/fluorescence wavelengths due to extended polymethine length, and limited photofunctionality. This limitation restricts their utility in specific applications requiring high-power excitation and/or a wash-free approaches. This study introduces novel merocyanine dyes, MCPY3 and MCPY5, comprising a newly developed pyrene-fused dioxaborine and polymethine chain. Despite their minimal polymethine lengths, their absorption/fluorescence wavelengths reside in the red to near infra-red regions due to the substantial π-conjugation system of pyrene. Moreover, they exhibit a considerably superior photostability to carbocyanine dyes and fluorogenic behavior between low (ON) and high (OFF) polar solvents, while maintaining brightness comparable to carbocyanine. Leveraging these advantages, the hydrophilic analogs of MCPY3, MCPY3S, were applied to two-photon microscopy imaging of the skin tissues on the finger of a living mouse. The dye clearly visualized the individual cell morphology in the epidermis and the elastin within the dermis, highlighting the potential of the new dye as a valuable tool for fundamental dermatological and histological studies.