Water- and oxygen-tolerant phosphorescent carbon nitrides enable visual hydrogel biosensing

Area of Science:

• Materials Science
• Organic Chemistry
• Nanotechnology
• Biomedical Engineering

Background:

• Metal-free room temperature phosphorescence (RTP) materials are promising for applications requiring long lifetimes and large Stokes shifts.
• Existing RTP materials struggle with stability in aqueous and oxygen-rich environments due to quenching effects.
• Developing robust, water- and oxygen-tolerant RTP materials is crucial for practical applications.

Purpose of the Study:

• To engineer stable, metal-free room temperature phosphorescent (RTP) materials for aqueous environments.
• To overcome the limitations of water and oxygen sensitivity in organic phosphorescent materials.
• To demonstrate the utility of these materials in biosensing applications.

Main Methods:

• Developed a 'trinity strategy' integrating emissive units, excited-state stabilization, and protection within a single polymeric carbon nitride (CN) macromolecule.
• Functionalized the carbon nitride macromolecule with imidazolium to create a hydrophobic microenvironment.
• Investigated the phosphorescence properties, lifetimes, quantum yields, and mechanistic pathways using spectroscopic techniques.

Main Results:

• Achieved homogeneous RTP materials with robust phosphorescence in water and oxygen, exhibiting lifetimes up to 80 ms and high quantum yields.
• Mechanistic studies indicated efficient intersystem crossing facilitated by incompletely condensed residues, stabilized by the CN skeleton, and protected by the hydrophobic imidazolium functionalization.
• Fabricated a phosphorescent hydrogel demonstrating visual detection of Fe3+ in human serum.

Conclusions:

• Engineered carbon nitride serves as a versatile platform for creating stable, water/oxygen-tolerant organic RTP materials.
• The developed materials show significant potential for advanced biosensing applications.
• This work paves the way for novel applications of metal-free phosphorescent materials in biological and environmental monitoring.