Developments in near-infrared fluorescent probes for G-quadruplexes structures

The G-quadruplex (G4) represents a noncanonical guanine-rich nucleic acid secondary structure characterized by the presence of two or more G-quartets stabilized through Hoogsteen hydrogen bonding. These structures play essential roles in various biological processes including DNA replication, gene expression regulation, telomere maintenance, and genomic stability. Effectively visualizing and precisely detecting G4 structures and their dynamic changes in cells and in vivo are crucial for elucidating the relationship between different G4 structures and functions within complex biological systems. Among the plethora of G4 probes studied, near-infrared (NIR) G4 fluorescent probes are highly sought after due to their minimal autofluorescence and low cellular damage. The significance of NIR G4 fluorescent probes lies in their application for in-depth imaging and in vivo studies, providing excellent resolution with minimal perturbation of the organisms. This review comprehensively examines recent advancements of NIR G4 fluorescent probes for in vitro, cellular, and in vivo imaging, considering various G4 molecular backbones. The discussion encompasses the photophysical properties, binding affinity to G4, molecular design strategies, and modification concepts of NIR G4 fluorescent probes. Finally, this review is designed on the existing challenges and future development potential of G4 imaging tools.