Researchers induce photosynthetic bacteria to absorb carbon nanotubes by wrapping nanotubes in protein (Nat. Nanotechnol. 2022, DOI: 10.5281/zenodo.67777770). The study's authors say the findings could lead to a new class of biosensors, and photovoltaic devices, and allow detailed study of bacterial cellular mechanisms.
It has been previously shown that bacteria can absorb other nanomaterials such as gold nanoparticles and luminescent quantum dots. But scientists prefer to use carbon nanotubes because they fluoresce stably at near-infrared (NIR) wavelengths that do not overlap with the wavelengths naturally emitted by bacteria and other cells. Nanotubes in cells can be detected clearly for a long time, which will aid in imaging and sensing.
Scientists have used nanotubes in mammalian cells to perform near-infrared imaging of drug delivery and cell metabolism. However, while mammalian cells can actively swallow nanotubes, the bacterial cell membrane is more complex and does not allow nanotubes to pass through.
To solve this problem, Ardemis Boghossian, a chemical engineer at the Federal Institute of Technology of Lausanne (EPFL), and colleagues tried several protein and peptide-based coatings to change the surface charge of nanotubes. “The outer membrane of the bacteria is negatively charged,” she said. "When wrapped in something positively charged, [nanotubes] are able to enter the inside of the cell."
The team inserted the coated nanotubes into cyanobacteria, which generate energy through photosynthesis using . The researchers found that nanotubes act like a wire that shuttles the charges generated inside bacteria to the outside. Bacterial colonies with nanotubes produce 15 times the current that bacteria without nanotubes produce. As the concentration of nanotubes increases, the amount of current increases, but is limited to the limit. When the concentration is too high, nanotubes tend to kill bacteria.
To the researchers' surprise, bacteria also passed on nanotubes to their offspring. When bacteria divide, offspring inherits the nanotubes and part of the parental cell membrane. “This inherited nanobionics is a big novelty,” Boghossian said. "It's like you have someone with bionic eyes or arms, let their children inherit it." Researchers can image bacteria when they use NIR fluorescence of nanotubes. “Nanotubes can also be used as optical sensors to monitor bacteria’s metabolism,” Boghossian added.
"Carbon nanotubes are an important tool in optoelectronics," said Massimo Trotta, chemist at the Italian National Research Council. He said the work shows that bacterial cells can absorb nanotubes without affecting their growth and division. Trotta hopes that this idea can be further used to develop novel bacterial biosensors and bio photovoltaic with a “lower carbon footprint and smaller environmental impact”.
