Self-assembled luminescent lanthanide complexes in solution as rising stars for sensing and bioimaging

Luminescent lanthanide (Ln³⁺) complexes are highly attractive for diverse applications, particularly as luminescent probes, owing to their exceptional photophysical properties, including long-lived photoluminescence, narrow-band emissions, and large Stokes shifts. These characteristics enable advanced techniques like time-gated detection, significantly enhancing signal-to-noise ratios in biological samples. Traditional luminescent Ln³⁺ complexes are characterized by bulky organic cryptands and/or conjugated chromophoric antennae for prompting the metal excitation prior to emission. This strategy is usually synthetically demanding, including complexation reactions that last for several days. To overcome this limitation, self-assembly strategies in solution have recently emerged as a powerful approach. This review discusses recent advancements in self-assembled luminescent Ln³⁺ complexes across various solvents, with particular emphasis on their behavior and performance in aqueous environments. It highlights the growing importance of water-compatible self-assembled luminescent Ln³⁺ complexes for biological applications, underscoring their potential in cell imaging and biosensing. By addressing key design challenges and showcasing diverse functionalities, this review provides a comprehensive and accessible overview for researchers in chemistry, biochemistry, and biology interested in the rapidly evolving field of lanthanide luminescence.