Single walled carbon nanotubes (SWCNTs) have found a wide range of applications due to their versatile photophysical and electronic properties. As environmentally sensitive fluorophores, SWCNTs have been employed as nanosensors for the detection of diseases, for monitoring biological environments, and for the detection of food quality, explosives and nerve agents. As tunable semiconductors absorbing light at visible wavelengths, SWCNTs have been used for light harvesting and for photocatalysis. SWCNTs also show potential as single photon emitters in the telecommunications wavelength range, with applications in quantum computing. A common strategy for employing SWCNTs as biosensors involves using single stranded DNA as a wrapping agent. Single stranded DNA has been found to bind strongly to SWCNTs due to π-π stacking interactions between the aromatic nucleotide bases and the SWCNT sidewalls. This affords a strong, flexible wrapping agent which shows excellent colloidal stability in aqueous environments, well suited for biosensing applications. Furthermore, certain DNA sequences have been found to have particularly strong affinity for specific chiralities of DNA, and so have been used for SWCNT sorting and single chirality purification. In order to tailor the photophysical properties and environmental responsivity of SWCNT sensors, it is common practice to covalently modify the nanotube surface. This results in the formation of nanotubes with quantum defects or "color centers" that fluoresce brightly in the shortwave IR spectrum, referred to herein as color center nanotubes (CCNTs). In recent years, the majority of CCNT synthesis was performed using aryl diazonium salts to attach aryl rings as structural 'defects' on the nanotube surface. Formation of these defects results in a loss of sp 2 hybridization at the defect site and formation of two sp 3 centers. This alters the fluorescence properties of the nanotubes, including the formation of a new emission peak (referred to as E11 -, in contrast to the E11 emission peak of unmodified nanotubes). The choice of aryl group has a significant impact on the quantum well depth and environmental responsivity of the nanotubes-for example, incorporation of protonatable aniline derivatives on the nanotube surface results in nanotubes which respond to changes in pH. Formation of CCNTs using aryl diazonium salts is typically performed using SWCNTs dispersed in surfactant, superacid solutions or the use of a light source to induce photothermal heating of nanotubes and promote electronic transfer between the nanotube and diazonium. Functionalization of surfactant-dispersed nanotubes is typically performed over a time frame of hours to days , and require subsequent surfactant removal in order to suspend the CCNTs with biologically-compatible wrappings such as DNA. Concentrated acid solutions are incompatible with acid-reactive functional groups, limiting the scope of possible aryl defects. Concentrated sulfuric or chlorosulfonic acid solutions are also dangerous to the user, and neutralization steps following functionalization can generate large amounts of heat and smog, with the risk of ignition depending on the choice of reactant. Light-mediated chemistry suffers from poor scalability due to poor light penetration into large volumes of concentrated nanotubes. SWCNTs wrapped with organic polymers have also been previously functionalized using diazonium salts, but these reactions require overnight incubation and are performed in organic solvents which are incompatible with DNA-wrapped CCNTs. We describe herein the synthesis of DNA-wrapped CCNTs using hydrogen peroxide as a reducing agent to generate aryl radicals from aryl diazonium salts in the presence of DNA-wrapped SWCNTs (Scheme 1). The reaction uses very mild conditions, and can be performed at room temperature in aqueous solutions over a time frame of minutes, with the primary by-products being small amounts of nitrogen and oxygen gas. This reaction can be monitored in real-time via fluorescence analysis within a microtiter plate, affording fine control over the degree of functionalization. Peroxidemediated aryl functionalization of nanotubes can be performed using pristine, undispersed nanotubes, or with ssDNA or surfactant-based polymer wrappings. In the case of ssDNA-wrapped nanotubes, the functionalization did not appear to disrupt the existing ssDNA wrapping, and aqueous washing could be performed to terminate the functionalization reaction whilst leaving a dispersed solution of nanotubes. This technique is therefore compatible with polymer-based nanotube purification techniques such as DNAbased nanotube sorting , as nanotubes can be functionalized immediately after purification. This results in the production of CCNTs with a high degree of control over both chirality and degree of functionalization. Finally, this reaction can be performed with in situ generation of diazonium salts from anilines, enabling substantial scalability and versatility with a large variety of functional groups.