A recent study has unveiled the development of dual-stimuli-responsive fluorescent supramolecular vesicles crafted from europium complexes and polypseudorotaxanes (PPRs), enhancing fluorescence and tunability for practical applications.
Published on March 3, 2025, this groundbreaking research addresses significant challenges associated with the application of lanthanide ions, renowned for their exceptional optical properties, yet often hindered by quenching issues related to their coordination environments. By utilizing host-guest interactions facilitated by carboxymethyl-β-cyclodextrin (CMCD) and Pluronic copolymers, the researchers successfully encapsulated europium complexes within these novel supramolecular structures.
Europium complexes are known for their prolonged luminescence, but their applications are often inhibited due to high-frequency oscillation effects from solvent molecules surrounding their coordination sphere. The primary goal of this research was to create stable vesicles to address these issues, and the results are promising.
The dual-responsive nature of the developed supramolecular vesicles allows for size and fluorescence adjustments through simple manipulation of external conditions. Specifically, the fluorescence intensity can be regulated by the addition of enzymatic stimuli, such as α-amylase, which leads to the gradual dissociation of the vesicles, resulting in significant quenching of fluorescence. This characteristic is anticipated to facilitate smart drug delivery systems, effectively communicating with the surrounding biochemical environment.
The researchers assembled fluorescent vesicles by adjusting the host-guest ratio (H/G) of the components, particularly varying the concentration of F127 and CMCD to customize the formation and size of the vesicles without compromising their performance. The minimal hydrophobic interaction, along with the effective encapsulation of europium complexes, enhances the vesicles’ fluorescence properties, making them viable candidates for biomedical applications.
Observations revealed the aggregates possessed hydrodynamic sizes ranging between 372 to 690 nanometers, indicating versatility depending on PPR component ratios. Remarkably, fluorescence intensities of these assemblies significantly increased when eu[III] complexes were coordinated with PPRs, achieving nearly fourfold enhancements when compared to conventional structures without such interactions.
Experimental results demonstrated the qualitative stability of the supramolecular assembly, showcasing enhanced quantum efficiencies and reduced non-radiative pathways, which are often detrimental to photophysical performance. These findings indicate the potential application of these vesicles not only for fluorescence imaging but also for targeting specific sites within biological systems.
These innovative vesicles respond dynamically to changes, including pH levels. Lowered pH levels, achieved through the introduction of HCl, resulted in decreased fluorescence intensity, which underscored the material’s capacity for environmental responsiveness. This pH sensitivity is particularly advantageous for smart drug delivery, releasing therapeutics at the desired target sites efficiently.
To verify their findings, the research team employed various characterization techniques, including fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). These analyses confirmed the luminescent and structural attributes of the vesicles, supporting their suitability for advanced biomedical applications.
Overall, the study presents significant advancements toward the development of multifunctional supramolecular vesicles based on lanthanide complexes. The ability to tune size and fluorescence properties, coupled with their responsiveness to enzymatic and pH stimuli, positions these materials at the forefront of innovative biomedical technologies aimed at enhancing drug delivery and diagnostic processes.