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Thursday, July 18, 2013

Sterilizing without electricity

A key feature in medical care that does more good than harm is the ability to properly sterilize instruments. This is tricky enough in modern hospitals, which are constantly battling outbreaks of MRSA and biofilms. Imagine how difficult it is in regions of the world without access to electricity. Rice University researchers are working to remedy that problem by adding nanoparticles to autoclaves.

Autoclaves are devices that sterilize equipment by exposing them to high pressure steam. If used properly, an autoclave will denature proteins, effectively destroying not only microbes but viruses and spores as well. Unfortunately, most autoclaves rely on electricity to create the super hot steam they require. Enter light-absorbing nanoparticles.

When suspended in liquid, these tiny particles act as nucleation points that convert solar energy to steam at 80% efficiency. The small bubbles of vapor around each nanoparticle grow and spread throughout the liquid, even though the temperature of that liquid has not reached boiling. With enough exposure to sunlight, the liquid does eventually boil, leading to steam that is much hotter than what could be achieved without the presence of the nanoparticles. The nanoparticles are not damaged or degraded by this process and can be reused indefinitely.

The researchers found that their solar nanoparticle autoclaves were capable of maintaining a temperature of 115°C for over 30 minutes, more than sufficient to achieve complete sterilization. Remember, this was done without electricity.

To be fair, the authors did make use of parabolic solar collectors to funnel the sun’s energy into their autoclaves more efficiently. I don’t mean to give the impression that you could just sit a can of nanoparticle-containing water in a field somewhere and turn it into an autoclave. Still, once you buy or construct your equipment, you have no more material or energy costs. That should be an enormous help in many poor communities.


Oara Neumanna, Curtis Feronti, Albert D. Neumann, Anjie Dong, Kevin Schell, Benjamin Lu, Eric Kim, Mary Quinn, Shea Thompson, Nathaniel Grady, Peter Nordlander, Maria Oden, & Naomi J. Halas (2013). Compact solar autoclave based on steam generation using broadband light-harvesting nanoparticles Proceedings of the National Academy of Sciences of the United States of America DOI: 10.1073/pnas.1310131110.