Covalent organic frameworks as nanocarriers of tailored BODIPY for phototheragnostic applications

Abstract

Grafting fluorophores and photosensitizers onto nanocarriers is recognized as an effective strategy for fluorescent bioimaging and photodynamic therapy. This approach enhances targeted drug delivery to tumor sites, while improving the biocompatibility and stability of poorly water-soluble bioprobes, thereby reducing side effects. Among the available organic dyes and nanoparticles, BODIPY and COF stand out as a compatible pair for this purpose. To leverage the COF-BODIPY scaffold as photoactive platform for biomedical applications, we have optimized their integration. To this aim, firstly BODIPY units were functionalized to enable strong binding to specific sites of the COF via click chemistry, positioning the BODIPY within the pore of the COF. Following this approach, BODIPY derivatives photoactive across different spectral regions (from green to red window) were straightforwardly grafted onto the COF. The structural and photophysical properties of these nanomaterials were thoroughly characterized. Notably, the COF bearing styrylated and iodinated BODIPY was especially appealing due to its dual photonic performance, enabling both singlet oxygen generation and red fluorescence under long-wavelength excitation. Upon its cellular uptake by human melanoma cells, this dyed nanoparticle selectively stained lysosomes, and at the same time triggered a cytotoxic response to induce cell death under illumination with red light, thus being a suitable candidate for theragnostic purposes.