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Few chemical methods controllably generate sp3 defects on single-walled carbon nanotubes, and fewer still create quantum wells that localize excitons and enhance near-infrared emission. Here we describe an aqueous, nanotube-catalysed Fenton reaction that enables the conjugation of an extensive range of small molecules lacking traditional single-walled carbon nanotube conjugation handles, generating quantum well defects with tunable electro-optical properties. We demonstrate the attachment of over 150 unique small molecules, including alcohols, amines, carbonyls, acrylates, amino acids and peptides. The resulting optical properties are governed by the electronic structure of the attached group, which determines the relative configuration of defects (ortho or para) within the graphitic lattice. Time-dependent density functional theory calculations confirm the assignment of the observed emission peaks to specific defect configurations. These molecularly driven effects enable precise control over the optical properties of the nanotubes, broadening the design space of rationally engineered quantum well-bearing nanomaterials. 

Atomic defect color centers in solid-state systems hold immense potential to advance various quantum technologies. However, the fabrication of high-quality, densely packed defects presents a significant challenge. Herein we introduce a DNA-programmable photochemical approach for creating organic color-center quantum defects on semiconducting single-walled carbon nanotubes (SWCNTs). Key to this precision defect chemistry is the strategic substitution of thymine with halogenated uracil in DNA strands that are orderly wrapped around the nanotube. Photochemical activation of the reactive uracil initiates the formation of sp3 defects along the nanotube as deep exciton traps, with a pronounced photoluminescence shift from the nanotube band gap emission (by 191 meV for (6,5)-SWCNTs). Furthermore, by altering the DNA spacers, we achieve systematic control over the defect placements along the nanotube. This method, bridging advanced molecular chemistry with quantum materials science, marks a crucial step in crafting quantum defects for critical applications in quantum information science, imaging, and sensing. 

Autophagy is a cellular process with important functions that drive neurodegenerative diseases and cancers. Lysosomal hyperacidification is a hallmark of autophagy. Lysosomal pH is currently measured by fluorescent probes in cell culture, but existing methods do not allow for quantitative, transient or in vivo measurements. In the present study, we developed near-infrared optical nanosensors using organic color centers (covalent sp3 defects on carbon nanotubes) to measure autophagy-mediated endolysosomal hyperacidification in live cells and in vivo. The nanosensors localize to the lysosomes, where the emission band shifts in response to local pH, enabling spatial, dynamic and quantitative mapping of subtle changes in lysosomal pH. Using the sensor, we observed cellular and intratumoral hyperacidification on administration of mTORC1 and V-ATPase modulators, revealing that lysosomal acidification mirrors the dynamics of S6K dephosphorylation and LC3B lipidation while diverging from p62 degradation. This sensor enables the transient and in vivo monitoring of the autophagy–lysosomal pathway.