Heat given off by light bulbs has mostly been an undesirable side effect of since Edison first invented them. But at Rice University, researchers have started turning light into heat when needed, to set off biochemical reactions remotely on demand. The method makes use of materials derived from distinctive microbes known as thermophiles, which thrive at high temperatures but shut down at room temperature.
The project joins enzymes from these microbes with plasmonic gold nanoparticles. The nanoparticles heat up when exposed to near-infrared light, thus activating the enzymes, which in turn are able to carry out their functions.
In effect, this allows chemical processes to happen at lower temperatures. Since heating occurs only where needed, at the nanoparticle’s surface, where it activates the enzyme, the environment stays cooler. The method has good potential for industrial processes that require heat or benefit from remote triggering with light.
“Basically, we’re getting the benefits of high-temperature manufacturing without needing a high-temperature environment,” said Rice postdoctoral fellow Matthew Blankschien. “The challenge was to keep the higher temperature at the nanoparticle, where the enzyme is activated, from affecting the environment around it.”
Using Free Energy
“The implications are pretty exciting,” said Rice professor Michael Wong. “In the chemical industry, there’s always a need for better catalytic materials so they can run reactions more inexpensively, more ‘green’ and more sustainably. You shouldn’t run through gallons of solvent to make a milligram of product, even if you happen to be able to sell it for a lot of money.”
Potential energy savings alone might make the Rice process of interest to industry. “Here we’re using ‘free’ energy,” Wong said. “Instead of needing a big boiler to produce steam, you turn on an energy-efficient light bulb, like an LED. Or open a window.”
At the center of the process is a gold nanorod particle, 10 nanometers wide and 30 long, which heats up when hit with near-infrared light from a laser. The rods are the ideal size and shape to react to light of around 800 nanometers. The light excites surface plasmons that ripple like water in a pool, emitting energy as heat.
The nanoparticles are covered with a thermophilic enzyme, glucokinase, from Aeropyrum pernix. The A. pernix microbe was discovered in 1996, living near hot underwater vents off the coast of Japan. At around 176 degrees Fahrenheit, A. pernix degrades glucose, a process necessary to nearly every living thing. The enzyme can be heated and cooled repeatedly.
In the experiments, Blankschien and graduate student Lori Pretzer cloned, then purified and altered glucokinase enzymes so that they attached to the gold nanoparticles. The enzyme nanoparticle complexes were then suspended in a solution and tested for glucose degradation. When the solution was heated in bulk, they found the complexes became highly active at 176 degrees, as was expected.
The complexes were then encapsulated in a bead of gel-like calcium alginate. The gel helps keeps the heat in, while being porous enough to allow enzymes to react with materials around it. Under bulk heating, the enzymes’ performance dropped dramatically because the beads insulated the enzymes too well.
However, when encapsulated complexes were illuminated by continuous, near-infrared laser light, they worked substantially better than under bulk heating while leaving the solution at near-room temperature. The researchers found the complexes robust enough for weeks of reuse.
“As far-fetched as it sounds, I think chemical companies will be interested in the idea of using light to make chemicals,” Wong said. “They’re always interested in new technologies that can help make chemical products more cheaply.”
Other possible uses are envisioned for the new approach in the production of fuels from degradation of biomass like lignocellulose; for drug manufacture on demand, perhaps from nanoparticle-infused tattoos on the body; or even for lowering blood sugar concentrations as a different way to manage diabetes.
Light-Triggered Biocatalysis Using Thermophilic Enzyme–Gold Nanoparticle Complexes
Matthew D. Blankschien, Lori A. Pretzer, Ryan Huschka, Naomi J. Halas, Ramon Gonzalez, and Michael S. Wong
ACS Nano, Article ASAP DOI: 10.1021/nn3048445
Graphic courtesy Lori Pretzer/Wong Group