Nanotubes illuminate the way to living photovoltaics
Light-harvesting bacteria infused with nanoparticles can produce electricity in a "living photovoltaic". Credit: Giulia Fattorini

Professor ArdemisBoghossian is a professor at the School of Basic Sciences. That doesn't sound exciting on the surface, but it is. Researchers are putting nanotubes in cells that use mechanisms that are specific to those types of cells. There are additional challenges in getting particles through the tough exterior of the bacterium. This has very exciting implications in terms of applications, despite the barriers we've been able to overcome.

The research focuses on living cells. Combining the advantages of both the living and non- living worlds is what the "nanobionic" technologies are about. For years, her group has worked on the applications of single-walled carbon nanotubes and tubes of carbon atoms.

SWCNTs are ideal for a lot of novel applications. SWCNTs have been placed inside cells to monitor their metabolism. SWCNTs have been used for genome editing in plant cells, while in mammals they have been used for therapeutic drugs. SWCNTs can be used to image biological tissue deep inside the body.

It is the first time that fluorescent nanotubes have been used inbacteria.

In an article published in Nature Nanotechnology,Boghossian's group with their international colleagues were able to convincebacteria to take up SWCNTs by decorating them with positively charged proteins that are attracted by the negative charge of thebacteria's outer membrane. The two types ofbacteria explored in the study, Synechocystis and Nostoc, are part of a large group ofbacteria that get their energy through photosynthesis. They are "Gram-negative", which means that their cell wall is thin, and they have an additional outermembrane that "Gram-positive"bacteria don't.

The researchers found that the cyanobacteria were able to internalize SWCNTs. The SWCNTs were able to penetrate the cell walls with this process.

The team wanted to find out if the nanotubes could be used to image cyanobacteria. "We built a first-of-its-kind custom setup that allowed us to image the special near-infrared fluorescence we get from our nanotubes inside thebacteria."

Even though thebacteria emit their own light, you could see the nanotubes even though they weren't emitting it. The wavelength of the nanotubes is not in the blue. The signal from the nanotubes is very stable and clear, unlike any other sensor. We're excited because we can now use the nanotubes to see what is happening inside of cells that have been difficult to image using more traditional particles. The nanotubes stand out in these cells because they give off a light that no natural living material can give off.

'Inherited' is the word for 'inherited'.

The scientists were able to observe the growth and division of the cells in real time. They found that the daughter cells of the dividing microbe were sharing SWCNTs. The daughter cells have the properties of the nanotubes in common.

This is called "inherited nanobionics." It's like having an artificial limb that makes you better than you can be. Imagine if your children inherit the property when they're born. The behavior is passed on to the descendants. It's the first time we've shown it.

There are living photovoltaics.

When we put the nanotubes inside thebacteria, they show a significant enhancement in the electricity it produces when it is illuminated by light. Our lab is trying to figure out how to use thesebacteria in a living photovoltaic system.

"Living" photovoltaics use organisms to produce energy. These devices are still in the early stages of development, but they represent a solution to our energy crisis and efforts against climate change.

There is a dirty secret in photovoltaics. A lot of CO 2 is released just to make most standard photovoltaics. Not only does it harness solar energy, but it has a negative carbon footprint as well. CO 2 is absorbed instead of being released. It solved two problems at the same time. These solar cells are not dead. You don't have to build a factory to build self-replicatingbacteria. They use CO 2 to make more of themselves. This is a dream of a scientist.

A living photovoltaic device that has automated control over electricity production that doesn't rely on the addition of foreign particles is envisioned by the author. The cost and environmental effects of putting nanotubes inside of cyanobacteria are the biggest roadblock to implementation.

With an eye towards large-scale implementation, the team is looking to synthetic biology for answers. Synthetic biology allows us to reprogram these cells. They can be engineered so that they can produce electricity.

More information: Ardemis Boghossian et al, Carbon nanotube uptake in cyanobacteria for near-infrared imaging and enhanced bioelectricity generation in living photovoltaics, Nature Nanotechnology (2022). DOI: 10.1038/s41565-022-01198-x Journal information: Nature Nanotechnology