Researchers Develop Tiny Gold Nanorods to Kill Bacteria

Researchers at Chalmers University of Technology in Sweden have developed a new technology. Small nanorods of gold heated with near-infrared light (NIR) can kill bacteria, making the surfaces of the implants sterile. The study results have been published in the journal Nano Letters.

“The gold rods absorb the light, the electrons in the gold are set in motion, and finally the nanorods emit heat. You could say that the gold nanorods work like small frying pans that fry the bacteria to death,” said Maja Uusitalo, a doctoral student at Chalmers and lead author of the study.

Nanometre-sized rods of gold are attached to the implant surface. Near-infrared (NIR) light hits the surface of the implant, turning the rods into tiny heating elements. The small, localized heating kills any bacteria on the surface of the implant without heating the surrounding tissue.

“The trick is to tailor the size of the rods. If you make them a little smaller or a little bigger, they absorb light of the wrong wavelengths. We want the light that is absorbed to penetrate skin and tissue well. Because once the implant is inside the body, the light must be able to reach the surface of the prosthesis,” commented Martin Andersson, Professor and research leader at Chalmers.

The researchers are now presenting a new study that increases the understanding of how the gold rods are affected by light and how the temperature in them can be measured.

Due to their tiny size, researchers could not measure the rods with a regular thermometer; instead, the researchers used X-rays to study how the gold atoms move. The method enables precise measurement of the temperature of the gold rods and how the temperature can be regulated using the intensity of the NIR light.

“We can control when the surface should be antibacterial and when it should not. When we turn off the light, the surface is no longer antibacterial and reverts to its original state. This is an advantage because many antibacterial surfaces usually have negative effects on healing,” Andersson said.

The gold nanorods themselves are completely passive on the surface before the NIR light heats them. Only then are the rods activated, becoming hot and triggering the antibacterial effect.

The technology with NIR-heated gold nanorods has previously been studied in cancer research, but the research group at Chalmers is the first to use the technology to create an antibacterial surface on implants with high precision and control.

Researchers hope to test this method on multiple implant materials such as titanium and different plastics. The end goal is to bring the technology to healthcare. 

Image: Chalmers University of Technology