Excited-State Conjugation/De-Conjugation Driven Nonradiative Thermal Deactivation for Developing Fluorogenic Probes to Diagnose Cancers

Structure-Activity Relationship of Hemicyanine Molecules: Mitochondrion-Targeting Hemicyanine Fluorescent Molecular Probes for HSO3- Recognition and Near-Infrared Image-Guided Photothermal/Photodynamic Synergetic Therapy

Hemicyanine molecules have unparalleled potential in the fields of fluorescence sensing, bioimaging, and disease therapeutics due to their excellent optical properties, cell penetration, potential mitochondrial targeting, and photosensitivity. Herein, three dual-cation hemicyanine molecular probes named DCy, PDCy, and TDCy were developed. All of them could detect HSO3-, and PDCy could recognize HSO3- under 365 nm ultraviolet light or sunlight. In addition, TDCy is a multifunctional molecule, which has the following advantages: simple synthesis, red and near-infrared dual-channel mitochondrial imaging, and photothermal/photodynamic synergistic therapy capabilities. Upon analysis of the correlation between the structures of the three hemicyanine molecules and HSO3- recognition, photosensitivity, photothermal activity, cell imaging, and cytotoxicity, the structure-activity relationship of the hemicyanine molecules could be summarized, which could provide guidance for subsequent research and development.

β-galactosidase instructed in situ self-assembly fluorogenic probe for prolonged and accurate imaging of ovarian tumor

Fluorescent probes are essential for optical imaging and have been extensively employed for precise cancer diagnosis studies. β-galactosidase (β-gal) serves as a primary biomarker for ovarian cancer and has been utilized to develop imaging probes for accurate tumor diagnosis. However, traditional small molecular probes have limitations in terms of rapid diffusion and metabolic clearance from the target lesion, resulting in a short imaging window and compromised tumor-to-background ratios (TBR). Herein, we integrated an enzyme-instructed in situ self-assembly strategy to construct Gal-IRFF, a small molecule-based activatable near-infrared (NIR) fluorogenic probe. Upon cleavage by endogenous β-gal overexpressed in ovarian cancer cells, IRFF exhibited enhanced NIR fluorescence signals and self-assembled into nanoparticles through intermolecular interactions of the Phe-Phe (FF) dipeptide moiety, which facilitated probe accumulation and retention within the tumor lesion. Compared with the small molecule probe Gal-IR, our proposed self-assembly probe Gal-IRFF demonstrated a lower limit of detection (LOD) towards β-gal and showed remarkable improvements in distribution and retention time within SKOV3 cells in vitro and tumors in vivo, thereby providing a long-term imaging window for real-time monitoring β-gal levels in ovarian tumors. Therefore, this study highlights the potential of an enzyme-instructed self-assembly fluorogenic probe design approach for achieving precise tumor diagnosis in vivo.

Fluorogenic polymethine dyes by intramolecular cyclization

Fluorescence imaging plays a pivotal role in the study of biological processes, and cell-permeable fluorogenic dyes are crucial to visualize intracellular structures with high specificity. Polymethine dyes are vitally important fluorophores in single-molecule localization microscopy and in vivo imaging, but their use in live cells has been limited by high background fluorescence and low membrane permeability. In this review, we summarize recent advances in the development of fluorogenic polymethine dyes via intramolecular cyclization. Finally, we offer an outlook on the prospects of fluorogenic polymethine dyes for bioimaging.