Silver nanoparticles are highlyindicated for a range of biologically interesting applications. Here we get the good news that nature hasbeen there ahead of us. Apparently the particleis formed through humic acid chemistry and they are simultaneously protected bythe acid to prevent immediate clumping or dissolution. They do in fact show up naturally.
The next question is to determinewhat other element(s) pulls the same trick. Nanoparticle process chemistry is slowly emerging as an important newtool and it is already an important method of medical delivery.
Recently we had a successful testdone with gold nanoparticles at MIT that established a certain size wouldpreferentially invade cancer cells allowing the cells to be heated andkilled. Silver may be even easier towork with in the same way.
It also explains the likelyreason for a number of erratic therapeutic effects of silver.
Silver cycle: New evidence for natural synthesis of silver nanoparticles
by Staff Writers
AFM (Atomic force microscopy) image of silver nanoparticles formed fromsilver ions in solution with humic acid. Color tone in this image indicatesheight (0 to 10 nanometers) above the base plane, so brighter spots are taller,larger nanoparticles. Image is roughly 1,700 nm on a side. Credit: MacCuspie, NIST
Nanoparticles of silver are being found increasingly in the environment-and inenvironmental science laboratories. Because they have a variety of usefulproperties, especially as antibacterial and antifungal agents, silvernanoparticles increasingly are being used in a wide variety of industrial andconsumer products.
This, in turn, has raised concerns about what happens to them oncereleased into the environment. Now a new research paper adds an additionalwrinkle: Nature may be making silver nanoparticles on its own.
A team of researchers from the Florida Institute of Technology (FIT),the State University of New York (SUNY), Buffalo, and the National Institute ofStandards and Technology (NIST) reports that, given a source of silver ions,naturally occurring humic acid will synthesize stable silver nanoparticles.
"Our colleague, Virender Sharma, had read an article in which theywere using wine to form nanoparticles. He thought that, based on the similarchemistry, we should be able to produce silver nanoparticles with humicacids," explains FIT chemist Mary Sohn.
"First we formed them by traditional methods and then we tried oneof our river sediment humic acids. We were really excited that we could see thecharacteristic yellow color of the nanoparticles."
Samples were sent to Sarbajit Banerjee at SUNY Buffalo
"Humic acid" is a complex mixture of many organic acids thatare formed during the decay of dead organic matter. Although the exactcomposition varies from place to place and season to season, humic acid isubiquitous in the environment. Metallic nanoparticles, MacCuspie explains, havecharacteristic colors that are a direct consequence of their size. Silvernanoparticles appear a yellowish brown.
The team mixed silver ions with humic acid from a variety of sources atdifferent temperatures and concentrations and found that acids from river wateror sediments would form detectable silver nanoparticles at room temperature inas little as two to four days.
Moreover, MacCuspie says, the humic acid appears to stabilize thenanoparticles by coating them and preventing the nanoparticles from clumpingtogether into a larger mass of silver.
"We believe it's actually a similar process to how nanoparticlesare synthesized in the laboratory," he says, except that the lab processtypically uses citric acid at elevated temperatures.
"This caught us by surprise because a lot of our work is focusedon how silver nanoparticles may dissolve when they're released into theenvironment and release silver ions," MacCuspie says.
Many biologists believe the toxicity of silver nanoparticles, thereason for their use as an antibacterial or antifungal agent, is due to theirhigh surface area that makes them an efficient source of silver ions, he says,but "this creates the idea that there may be some sort of natural cyclereturning some of the ions to nanoparticles."
It also helps explain the discovery, over the past few years, of silvernanoparticles in locations like old mining regions that are not likely to havebeen exposed to man-made nanoparticles, but would have significantconcentrations of silver ions.
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