Using household bleach and light, MIT researchers have created fluorescent quantum defects in carbon nanotubes. The defects can be synthesized quickly and at large scale, the researchers said. The researchers treated carbon nanotubes at room temperature with NaClO (bleach) and irradiated the nanotubes with ultraviolet light for less than a minute to achieve optimized oxygen-doping. The doping efficiency was controlled by varying surfactant concentration and type, NaClO concentration, and irradiation dose. Submerging a carbon nanotube in bleach produces an oxygen atom (red) that reacts with the carbon atoms (black) of the nanotube, forming a fluorescent quantum defect when irradiated with ultraviolet light. Courtesy of the Belcher Lab. After the fluorescent defects were created, the nanotubes became brighter and the emission of the carbon-nanotube-based defects shifted to the shortwave IR region (900-1600 nm). Variance spectroscopy, which the team used in collaboration with researchers from Rice University, revealed that most of the individual nanotubes in optimally treated samples showed both pristine and doped emission. It also helped the researchers monitor the quality of the quantum defects and determine the correct synthetic parameters. Bright fluorescent quantum defects could be used to upgrade current biomedical imaging systems, enabling researchers to look at even smaller tumors through the defect emission. Courtesy of the Belcher Lab. The researchers used fluorescent quantum defects created in carbon nanotubes to demonstrate a bio-imaging application that delivered high-contrast short-wavelength IR fluorescence images of vasculature and lymphatic structures in mice injected with only about 100 ng of the doped nanotubes. “We have demonstrated a clear visualization of vasculature structure and lymphatic systems using 150 times less [the] amount of probes compared to [the] previous generation of imaging systems,” professor Angela Belcher said. The defect carbon nanotube-based optical probes could improve imaging performance for image-guided surgery and earlier detection of cancer. The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-10917-3).
