Scientists have come up with a new method for killing bacteria in just seconds. Using highly porous gold nanodisks and light, the technique could help hospitals treat some common infections without applying antibiotics in the future. In turn, this would help to reduce the spread of antibiotics resistance.
The technique involves the creation of gold nanoparticles by dissolving gold in labs. The precious metal is reduced into smaller and smaller fragments, until the pieces can only be measured in nanometers (one nanometer is one billionth of a meter). Once reduced, the particles can then be shaped into disks.
"We showed that all of the bacteria were killed pretty quickly . . . within 5 to 25 seconds. That's a very fast process," said Wei-Chuan Shih, who works as a professor in the electrical and computer engineering department at the University of Houston in Texas.
Gold nanoparticles are highly sensitive to light absorption, rapidly converting photons into heat and getting hot enough to destroy different kinds of nearby cells, including cancer and bacteria cells.
In 2014, Shih and his research team created a new type of gold disk-like nanoparticle that measures a few hundred nanometers in diameter. The nanodisks are porous and have a spongy appearance, which increases their heating efficiency while at the same time preserving their stability.
In the next phase of the research process, the team aimed to experiment with the antimicrobial properties of the newly fashioned nanoparticles upon activation by light. The scientists grew bacteria in the lab, including E. coli and two forms of highly heat-resistant bacteria. The bacteria cells were then put on a coating of the tiny disks, and near infrared light from a laser was aimed at them. Subsequently, the team used cell viability tests and Scanning Electron Microscopy (SEM) imaging to see what percentage of cells survived the procedure.
The scientists were able to use a thermal imaging camera in order to demonstrate that the surface temperature of the particles hit temperatures as high as 180 degrees Celsius almost instantly, which killed almost all of bacterial cells were killed within 25 seconds. E. coli appears to be most susceptible to the treatment, with all of its cells dead after only seconds of exposure to the laser-far faster than conventional sterilization methods like boiling water or using dry-heat ovens, which can take minutes to an hour to work effectively.
Shih highlighted that this new technique has significant biomedical applications. "Any sort of light activated procedure would be much easier to implement at the bedside of a patient," he said. For example, the researchers are currently looking into using coatings of the nanoparticles on catheters, toward reducing urinary tract infections in hospitals.
The researchers are also investigating the potential integration of the nanoparticles with membranes in small water filters, in order to improve water quality.
The study was published March 17 in Optical Materials Express, a journal published by The Optical Society.
