What if we could harvest more sunlight & create useful products from it?
In school, I was learning about photosynthesis and how this is the holy grail of our world because it is the process that provides energy for the vast majority of life on Earth. Cool, right?
Currently, mostly plants, algae, and some microorganisms perform this.
Well … I’m here to crush your dreams 😎
Chlorophyll, the green pigment that plants use to harvest sunlight, is actually relatively inefficient.
- 28.2% of sunlight energy is actually collected by chlorophyll, of which 9% is collected as sugar → 35–40% of sugar is recycled/consumed by the leaf, leaving 5.4% net leaf efficiency.
Humans increasingly are looking to find alternatives to fossil fuels as sources of energy and feedstocks for chemical production.
So, plants aren’t very efficient at capturing sunlight, and humans need more sources of energy. That’s a problem.
But, don’t get ahead of yourself yet. Many scientists are working to create artificial photosynthetic systems (exactly what the name suggests) to generate renewable energy and simple organic chemicals using more captured sunlight.
These systems have an up-to 80% efficiency rate and are a zero-waste technology 🤯
How do These Artificial Photosynthetic Systems Work?
The goal is to enable the production of useful chemicals and fuels directly from sunlight and carbon dioxide, just like plants do. To make things quicker, I wrote an article on this here:
Here’s a quick recap:
- The idea is that we can use nano-materials which can efficiently use carbon dioxide from the air, capture toxic pollutants from water. Then, we take this excess captured CO2 and turn it into useful products.
- This is possible through artificial photosynthesis where we replicate the same process that plants undergo to make clean fuels and other products.
- Using catalysts we can turn carbon dioxide and water into chemical compounds containing one, two, three, or four carbon atoms with more than 99 percent efficiency.
- The carbon compounds can be used as building blocks to make useful materials.
Bacteria Has Entered The Chat
Another thing I learned in school was that most bacteria is not photosynthetic (meaning it doesn’t do photosynthesis) — regardless, plants are the most common. Not cool.
There are 298,000 species of plant on our planet 🌱. The number of bacteria on our planet will be five million trillion trillion — that’s a five with 30 zeroes after it. Fun fact: there are far more bacteria on earth than there are stars in the universe.
But some bacteria is actually photosynthetic (can undergo photosynthesis).
What are photosynthetic bacteria?
These micro-organisms are special types of bacteria that contain light absorbing pigments and reaction centers which make them capable of converting light energy into chemical energy.
Cyanobacteria contain chlorophyll while other forms of bacteria contain bacteriochlorophyll. Although bacteriochlorophyll resembles chlorophyll, it absorbs light of a longer wavelength than chlorophyll.
Bacteria with bacteriochlorophyll, do not use water as an electron donor and therefore do not produce oxygen (anoxygenic photosynthesis). Cyanobacteria perform photosynthesis using water as an electron donor in a similar manner to plants (oxygenic photosynthesis).
Not all bacteria have these unique properties. Since there is so much bacteria in the world + humans need more sources of energy, how can we help non-photosynthetic bacteria harvest light & create useful compounds?
Next Up: Nanoparticles
Nanoparticles are really great because they are almost like little solar panels → we can use them to capture sunlight.
Finally, let’s put the two ideas together and see how this is possible.
Bacteria + Nanoparticles = More Light Captured
To enable humans to capture more of the sun’s energy than natural photosynthesis can, scientists have taught bacteria to cover themselves in tiny, highly efficient solar panels [tiny semiconductor nanocrystals] to produce useful compounds.
Now, we can combine nanotechnology and biology, researchers are mimicking the processes that occur in the leaf of a plant to produce fuels such as butanol, biodegradable plastics and much more! Once combined with synthetic biology to precisely engineer the bacteria, the possibilities are endless.
Research at UC Berkeley:
There is research being done at UC Berkeley: (https://science.sciencemag.org/content/351/6268/74) to take bacterium named Moorella thermoaceticahas to perform photosynthesis for converting sunlight into valuable chemical products.
Artificial Photosynthesis Machine
Using inorganic semi-conductors (a semiconductor made from a non-carbon based material like silicon, gallium etc.) we can capture sunlight to organisms like bacteria that can then use the energy to produce useful chemicals from carbon dioxide and water within the bacteria.
Semi-Conductor: Cadmium Sulfide
Cadmium sulfide (CdS) have really unique properties involving the interaction of light with semiconductors.
They have been studied for:
- photoconductivity (the increase in electrical conductivity of a material as the result of the absorption of light) and;
- photovoltaic effects (the generation of electrical power as the result of absorption of light in a suitably designed material + a conversion from light energy to electrical energy).
On the more physics side: Cadmium Sulfide is also a well-studied semiconductor with a band structure and that is well-suited for photosynthesis. As both an “electrograph” (meaning it can undergo direct electron transfers from an electrode), and an “acetogen” (meaning it can direct nearly 90-percent of its photosynthetic products towards acetic acid).
We can use efficient light absorbers like Cadmium Sulfide semi-conductors to try and supercharge bacteria by covering their body with these [Cadmium Sulfide] semi-conductor nanocrystals.
So far, studies have been looking at naturally occurring non-photosynthetic bacteria called Moorella thermoacetica, which, as part of its normal respiration, produces acetic acid from carbon dioxide (CO2).
Acetic acid is a versatile chemical that can be readily upgraded to a number of fuels, polymers, pharmaceuticals and commodity chemicals through complementary, genetically engineered bacteria.
When you feed Cadmium and cysteine (sulfur-containing amino acid) to the bacteria, you can synthesize Cadmium Sulfide nanoparticles which function like solar panels on these bacterias surface.
A Zero Waste Technology
This produces acidic acid which is key for creating compounds, from CO2, water and light.
By growing the bacteria in tube-shaped reactors that are exposed to a light source, and giving them the sulfur-containing amino acid cysteine as an additional food source, they can achieve efficiency levels that make them ‘better than natural photosynthesis’.
The bacteria has an efficiency of more than 80% + the process is self-replicating, self-regenerating. Making this a 0 waste technology.
Once you cover this bacteria in these “tiny solar panels”, the bacteria can synthesize food, fuel, and plastics all using solar energy.
Electron Eaters — tuning Bacteria
Researchers are now trying to understand how these bacteria are able to basically eat electrons derived from the semiconductor and they’ve found some charge transfer between the semiconductor itself and [hydrogenase] enzymes found on the surface of this bacterium.
Now they can begin to tune and tweak the levers and optimize this interface, and develop more functional systems from that.
Gold Nanocluster + Bacteria
The bacteria, Moorella thermoacetica won’t work for free. UC Berkeley researchers have realized that when fed gold nanoclusters, the bacterium becomes even more efficient for producing solar fuels through artificial photosynthesis.
Check out this video to see how it works:
There are tons of plan is to eventually commercialize the system. They’re quite interested in trying to find other semiconductors that can be produced through this biosynthetic route, things like silicon or next-generation solar panel materials like indium phosphide.
Another possible avenue is to use synthetic biology and combining this with research like cellular agriculture can be even cooler ;)
If you’re in either [synthetic biology, cellular agriculture, microbiology, nanotechnology] or are passionate about this stuff, I’d love to connect and chat more about how we can advance this research!!
Interesting in keeping up to date with my journey?