Assembly of Dye Molecules in Covalent Organic Frameworks for Enhanced Colorimetric Biosensing.

Colorimetric assays have been extensively investigated for biosensing applications due to their advantages of visual recognizability, ease of use, and low cost. However, advancing their development is a great challenge due to the inherent limitations of colorimetric dyes. Herein, we report a strategy to assemble dyes in covalent organic frameworks (COFs) to effectively reinforce the applicability of pH-responsive dyes in colorimetric bioassays. Experimental results reveal that three-dimensional COFs can promote the assembly of dyes through hydrogen bonding, resulting in the formation of a dye-supermolecule@COF assembly. Consequently, when sensitized at increased pH levels (e.g., hydroxyl ions), disruption of hydrogen bonds may trigger a rapid transition from their insoluble fixed state within the COFs into soluble, visibly detectable dye anions. This process can also be facilitated by increased hydrophilicity and elevated electrostatic repulsion between the dye anions and COFs, leading to the substantial release of chromogenic dye anions from the COF pores into the solution, thereby amplifying the colorimetric signal output. Therefore, by employing various synthesized dye-supermolecule@COFs as signal tags, we developed a colorimetric bioassay capable of accurately identifying breast cancer cell subtypes. This study not only highlights the effectiveness of dye-supermolecule@COFs in enhancing colorimetric biosensing but also underscores the potential of employing the COF-mediated dye assembly strategy for colorimetric assays.