Click Chemistry on Defects to Create Multifunctional Fluorescent Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWCNT) are versatile materials for imaging and sensing in the near infrared (nIR) range. Non-covalent adsorption with (bio)polymers such as DNA is a powerful approach to functionalize SWCNTs. This approach lead to a broad range of biosensors. However, covalent approaches would be beneficial for many applications because of higher stability and photophysical signal transduction. One route to covalent functionalization is reactions with diazonium salts that create covalent defects and a red-shifted peak in the nIR fluorescence spectrum attributed to a formerly dark exciton.Here, we used novel synthesized diazonium salts to create defects that can be easily further functionalized with click chemistry reactions (Thiol-en and azid-alkine). The modified SWCNTs were additionally non-covalently wrapped in biopolymers for solubilization and characterized via nIR spectroscopy and atomic force microscopy (AFM). Using this approach we covalently conjugated diverse molecules including small aliphatic molecules, peptides, DNA and nanobodies to the SWCNT backbone. Successful functionalization was verified by conjugation of organic visible fluorophores and single SWCNT colocalization. Additionally, these multifunctional SWCNTs were used as building block for biosensors that detect disease markers.In summary, we present a general approach to conjugate a broad range of molecules to SWCNTs using defect chemistry and demonstrate applications in biosensing.