Light Triggers Biochemical Reactions

Biochemical reactions can now be remotely triggered on demand, thanks to a new technique that turns light into heat at the point of need on the nanoscale.

The method, created by Rice University researchers, uses materials derived from unique deep-sea microbes called thermophiles, which thrive at high temperatures but which shut down at room temperature. When enzymes from the microbes are combined with plasmonic gold nanoparticles that heat up when exposed to near-infrared light, the enzymes activate and carry out their functions.

This effectively allows chemical processes to happen at lower temperatures. And because heating occurs only where needed — at the surface of the nanoparticle, where it activates the enzyme — the environment stays cooler.

Chemical processes can be activated by light without the need for bulk heating of a material through a process developed by researchers at Rice University. The technique involves coating nanorods with thermophilic enzymes that are activated at high temperatures. Lighting the plasmonic gold nanorod causes highly localized heating and activates the enzyme. Courtesy of Lori Pretzer/Rice University.

“Basically, we’re getting the benefits of high-temperature manufacturing without needing a high-temperature environment,” said postdoctoral fellow Matthew Blankschien, who won the Peter and Ruth Nicholas fellowship two years ago to work on these ideas. “The challenge was to keep the higher temperature at the nanoparticle — where the enzyme is activated — from affecting the environment around it.”

At the center of the process is a gold nanorod about 10 nm wide and 30 nm long that heats up when hit with near-infrared light. The rods are just the right size and shape to react to light at around 800 nm. The light excites surface plasmons that ripple like water in a pool; in this case, emitting energy as heat.

In their experiments, the scientists cloned, purified and altered thermophilic glucokinase enzymes from Aeropyrum pernix so that they would attach 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, the complexes became highly active at 176 °F — the temperature at which the enzyme degrades glucose, a process necessary to nearly every living thing.

The complexes were then encapsulated in a gellike bead of calcium alginate, which helps keep the heat in but is 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.

But 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.

Members of the Rice team that created light-induced biochemical reactions include, from left, graduate student Lori Pretzer, professors Ramon Gonzalez, Michael Wong and Naomi Halas, and postdoctoral fellow Matthew Blankschien. Courtesy of Jeff Fitlow/Rice University.

The technique holds potential for industrial processes that now require heat or benefit from remote triggering with light.

“As far-fetched as it sounds, I think chemical companies will be interested in the idea of using light to make chemicals,” said Michael Wong, a professor of chemical and biomolecular engineering and of chemistry. “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.”

Other possible uses, Wong said, may include the production of fuels from degradation of biomass such as lignocellulose; for drug manufacture on demand — maybe for nanoparticle-infused tattoos on the body; or even for lowering blood sugar concentrations as a different way to manage diabetes.

“That we can now make these particles is great,” Wong said. “The next exciting part is in thinking about how we can deploy them.”

The study appeared in ACS Nano (doi: 10.1021/nn3048445).

For more information, visit: www.rice.edu