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Researchers at the University of Potsdam, Germany are using a Zetasizer Nano ZS from Malvern to measure the dimensions and stability of gold nanoparticles smaller than 5nm in diameter.

Gold has long been considered as an inert element, but in nanoparticulate form it can be very reactive.

For particles of less than 5nm, the surface electrons dominate the properties of the surface and consequently of the system.

This makes gold nanoparticles interesting for life-science applications, for example in tagging viruses and cells.

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 and stabilising agent.

To make the particles, a mixture of gold chloride and PEI in solution is heated to 100C.

This results in a dispersion of gold nanoparticles, which turn the solution red.

With the Zetasizer Nano the researchers were able to show that the average diameter of the particles was less than 5nm and to determine the zeta potential of the dispersion, an indicator of its stability.

Dr Kosmella said: ‘Being able to measure particle size is important for the determination of the hydrodynamic radius of the particles, including the polymer shell in comparison with other methods such as TEM, visualising the particle radius without polymer shell.’ The Zetasizer Nano ZS from Malvern enables the measurement of particle size, from 0.6 to 6000nm and zeta potential in a single instrument.

The technology built into the system provides the sensitivity required for measuring dilute proteins and polymers, as well as the ability to measure emulsions and suspensions at high concentrations.

It is the method of choice for nano-particle applications from routine colloid size measurements to the investigation of particulates at the leading edge of materials research.

Malvern Instruments

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