January 30, 2021. By Kolemann Lutz
Researchers from the University of Colorado Boulder developed light-powered nano-hybrid microbial factories that eat and convert CO2 by using light-activated quantum dots that fire specific microbial enzymes to generate biofuels, chemicals, and biodegradable plastics.
Intensive research has been conducted in combining multiple combinations of light, voltage, magnetic field stimulation to inorganic nanomaterials with metabolic networks in living cells. These attempts have been made to use direct light-activation in cell free extracts or purified enzymes for biocatalysis or bioelectrocatalysis. However, these strategies have limitations due to enzyme deactivation in air or during chemical conversion, without the ability to regenerate enzymes.
In 2013, the UC Boulder team began researching the applications of quantum dots (QDs): tiny nanoscopic (1X10-9 meter) semiconductors that are critical to nanotechnology systems. These QDs are injected into cells and later adapted, binded, and self-assembled to the electrochemical potential of the enzymes to wirelessly activate enzyme proteins using light, sound, or magnetic fields. The researchers investigated whether emitting artificial light to genetically engineered microbial cells with quantum dots could activate enzymes to convert airborne carbon dioxide and nitrogen even though the microbes cannot do so naturally because they are not photosynthetic.
The researchers designed and formed living nano-organisms using various strains of gram-negative soil bacteria, Azotobacter vinelandii (which fix nitrogen when grown aerobically) and Cupriavidus necator, hydrogen-oxidizing “knallgas” bacterium.
These non-photosynthetic microbes are typically dormant in water and release their gaseous byproducts to the surface, which are then harvested off the surface for manufacturing. These microbes and synthetic bacteria can generate electrons, reduce renewable chemical feedstocks like CO2, H2O, nitrogen, and air to carry out industrially important reactions.
By suspending normally nonphotosynthetic bacteria in buffered water without any sugar, the team engineered nanorganisms (nanorgs) to convert renewable feedstocks of air and CO2 directly into biofuels such as Isopropyl alcohol (IPA), hydrogen (H2), Butanediol (BDO), chemicals including formic acid, ammonia (NH3), and ethylene (C2H4), and the degradable bioplastic polyhydroxybutyrate (PHB).
By diffusing tailored quantum dots into the cells, the common microbes could accelerate their appetite for CO2 without sugar and with minimal sunlight to carry out the energy-intensive biochemical conversions. With an artificial light source radiating a light flux of 1.6mW/cm^2 for each of the ~10,000 biohybrid enzymes per nanorg, researchers estimated a 6-fold incident photons per enzyme turnover and achieved a high 13% quantum efficiency of enzyme activation using light.