New Microscopy Method Unveils Nanoparticle Release from Silverware and Jewelry

Since the emergence of nanotechnology, researchers, regulators and the public have been concerned that the potential toxicity of nano-sized products might threaten human health by way of environmental exposure.

Now, with the help of a high-powered transmission electron microscope, Keck grantees supported by a grant awarded in 2007 at the University of Oregon, captured never-before-seen views of miniscule metal nanoparticles naturally being created by silver articles such as wire, jewelry and eating utensils in contact with other surfaces. It turns out, the researchers say, humans have been in contact with nanoparticles for a long, long time.

The research – reported by Jim Hutchison and co-workers in ACS Nano (DOI: 10.1021/nn2031319) – focused on understanding the dynamic behavior of silver nanoparticles on surfaces when exposed to a variety of environmental conditions.

Using a new approach developed at the University, the team was able to directly observe microscopic changes in nanoparticles over time. The team found that silver nanoparticles deposited on the surface of their SMART Grid electron microscope grids (Figure 1A) began to transform in size, shape and particle populations within a few hours, especially when exposed to humid air, water and light (see Figure 1B). Similar dynamic behavior and new nanoparticle formation was observed when the study was extended to look at macro-sized silver objects such as wire or jewelry (Figure 2).

Figure 1: (A) SMART Grid platform used to capture silver nanoparticles for these studies. A molecular linker bound to the electron-transparent silicon dioxide window serves to bind particles to the surface through electrostatic interactions. (B) A difference map that shows the generation of new silver nanoparticles (blue color) and loss of silver (yellow) from the “parent particles” during exposure of the parent particles to humid conditions over five weeks.

Their findings show that nanoparticle ‘size’ may not be static, especially when particles are on surfaces. Thus, the initial size of a material may not be a good indicator of potential hazards to humans or the environment. In addition, the generation of nanoparticles from objects that humans have contacted for millennia suggests that humans have been exposed to these nanoparticles throughout time.

The findings challenge conventional thinking about nanoparticle reactivity and imply that the production of new nanoparticles is an intrinsic property of the material that is now strongly size dependent.

Figure 2: (A) Silverware in contact the SMART Grids during exposure to humid conditions. (B) Transmission electron microscope image showing silver nanoparticles generated while the silverware was in contact with the grids.

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