In remote, resource-poor locations, the lack of readily available sterilisation processes for medical or dental tools increases the risk of disease propagation.
Now, researchers from Rice University in the United States have developed two prototype sterilisation devices that harness the sun's power: one to sanitise medical equipment and the other to sterilise human waste without the need for an external electricity source. Their work was published in Proceedings of the National Academy of Sciences last month (8 July).
Both devices are modified versions of the steam-based autoclave systems used in modern medical facilities to eradicate infectious microorganisms from surfaces and liquids with a blast of high-pressure steam.
"Although steam-based sterilization is the primary method of choice for the processing of medical waste in the developed world, the large energy requirement for operation is the fundamental limitation for its adoption in developing countries, with limited or nonexistent access to sources of electricity sufficient to power such systems," the study says.
The new devices consist of a vessel containing water and gold nanoparticles that is placed in sunshine collected using a solar dish. The nanoparticles absorb the sunlight and this heat produces steam.
The process does not damage the nanoparticles, so they can be reused.
The systems maintain temperatures between 115 and 132 degrees Celsius for the time period sufficient to sterilise the contents of a 14.2 litre volume, which is in accordance with US Food and Drug Administration sterilisation guidelines.
Both devices passed the standard test of killing a reference strain of the heat-resistant bacteria Geobacillus stearothermophilus — used to check the performance of standard steam-based autoclave systems — in a sample over 30 minutes.
The researchers say their prototypes could be altered to provide steam for direct use in water purification, cooking, or electricity generation. However, they declined to comment on whether the devices have been field-tested, who will produce them and how they will be made available to developing countries.
Lead researcher Naomi Halas, professor of biomedical engineering at the university, tells SciDev.Net: "We would prefer not to answer questions regarding our technology. Any information not disclosed in our paper is not for public knowledge at the present time."
Tony Collins, managing director of UK-based autoclave manufacturer Priorclave, says that the devices could have a significant impact in developing countries, but also suggests a modification.
"Some consideration should be given to a method of ensuring the items to be sterilised stay at or above the required temperature for the required time without having to watch the process," he says.
Hilmi Salem, a research professor and director-general of the Applied Sciences and Engineering Research Centres at Palestine Technical University, says that the use of gold nanoparticles raises questions about cost and whether the devices will be affordable to poor communities.
"It remains to be seen whether the apparatus and technical support will be available to them under manageable and suitable terms," Salem adds.
> Link to the paper
See below for a video of researchers creating solar steam using nanoparticles
See below for a video of solar steam being used to clean human waste