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Tiny gold radiators ‘fry’ bacteria on medical implants

Scientists have shown that by heating up small nanorods of gold with near-infrared light (NIR), bacteria are killed, and the surface of the implant becomes decontaminated.

A team of surgeons transplanting a pig kidney into a brain dead patient, part of a growing field of research aimed at advancing cross-species transplants and closing the organ donor gap
A team of surgeons transplanting a pig kidney into a brain dead patient, part of a growing field of research aimed at advancing cross-species transplants and closing the organ donor gap - Copyright NYU Langone Health/AFP Joe Carrotta
A team of surgeons transplanting a pig kidney into a brain dead patient, part of a growing field of research aimed at advancing cross-species transplants and closing the organ donor gap - Copyright NYU Langone Health/AFP Joe Carrotta

Aiming to discover an alternative method to help overcome antibiotic resistance, a new technology from Chalmers University of Technology (Sweden) offers an important medical application. This is for when hip and knee implants are surgically inserted.

Scientists have shown that by heating up small nanorods of gold with near-infrared light (NIR), bacteria are killed, and the surface of the implant becomes decontaminated.

The technology with NIR-heated gold nanorods had previously been studied in cancer research. The application for surgical implants represents an alternative use in seeking to create the antibacterial surface on the implants.

There is a risk infections can occur during surgical procedures. The risk is elevated when foreign materials, such as knee prostheses, are implanted into the body. This is because the presence of the material weakens the body’s immune system. To help counter this, antibiotic treatments are commonly used.

Yet, the use of antimicrobials entails a risk of increased antibiotic resistance.

The new technology uses nanometre-sized rods of gold. These are attached to the implant surface. When NIR light hits the surface of the implant, the rods heat up and act as tiny heating elements.

The gold nanorods are completely passive on the surface before the NIR light heats them. Since the heating elements are so small, there is only ‘local heating’, which kills any bacteria on the surface of the implant without affecting the surrounding tissue.

This occurs as the gold rods absorb the light which causes the electrons in the gold to be set in motion. At a given threshold, the nanorods emit heat. NIR light is invisible to the human eye; however, it has the ability to penetrate human tissue. This means the gold nanorods can be heated on the surface of the implant inside the body by illuminating the skin.

The most important factor is getting the size of the rods exact. If they are too small or too big they will absorb light of the wrong wavelengths. The size of the gold nanorods is 20 by 70 nanometres and they absorb light in the NIR region around 800 nanometres.

The researchers are working on an additional study that increases their understanding of how the gold rods are affected by light and which assesses how the temperature in them can be measured.

Due to their tiny size the rods cannot be measured with a regular thermometer. Instead the researchers resorted to X-rays in order to study how the gold atoms move. This 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.

The temperature needs to be carefully controlled. If it is too high this will cause the nanorods to lose their shape and transform into spheres. This means they lose their optical properties and can no longer absorb NIR light effectively.

The research appears in the journal Nano Letters. It is titled “Photothermal properties of solid-supported gold nanorods.”

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Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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