Researchers at the University of Potsdam, Germany, are using a
Zetasizer Nano ZS from Malvern Instruments to measure the
dimensions and stability of gold nanoparticles smaller than 5 nm
in diameter. Gold has long been considered as an inert element,
but in nanoparticulate form it can be very reactive. For
particles under 5 nm the surface electrons increasingly dominate
the properties of the surface and consequently of the system.
This makes gold nanoparticles interesting for life science
applications, in tagging viruses and cells for example. Sabine
Kosmella and Joachim Koetz made the ultrafine nanoparticles in a
one-step reaction using gold chloride and an oligosaccharide-
modified hyper-branched polyethylenimine (PEI). The PEI is a
polyelectrolyte that acts as a reducing agent as well as a
stabilising agent. To make the particles, a mixture of gold
chloride and PEI in solution is heated to 100 degC. This results
in a dispersion of gold nanoparticles, which turn the solution
red. With the Zetasizer Nano the r