Measuring the Particle Size of Functionalized Gold Nanoparticles by DLS: Why the Weighting Model Matters

Gold nanoparticles (AuNPs) are an upcoming technology with applications in fields such as biomedical science, diagnostics and the food industry. Due to their excellent conductive properties, AuNPs are also used in electronics, as electronic chips or printable inks. Another interesting property of AuNPs is the relative ease with which they can be covalently linked to a large variety of organic and inorganic substances. In combination with their non-toxicity and excellent stability, this makes them attractive candidates for numerous biomedical in vivo applications such as in cancer therapy or diagnostics.

In solution, AuNPs are dispersed colloids which are thermodynamically instable due to their large surface-to-volume ratio. Without any protective ligands or electrostatic protection, the nanoparticles will form aggregates. Stabilization can however be greatly improved by attaching charged molecules or sterically stabilizing ligands on the particles’ surface, which are spatially demanding and prevent the gold particles from aggregating.

In previous application reports we have already demonstrated that Litesizer™ particle analyzers can determine the particle size of unmodified gold nanoparticles by Dynamic Light Scattering (DLS) with excellent accuracy and repeatability. In the present study we demonstrate that the Litesizer™ can also accurately determine the particle size of so-called functionalized gold nanoparticles, i.e. gold nanoparticles coupled to molecules having a stabilizing effect on the resulting colloid. We have studied gold nanoparticles functionalized by 1-dodecanethiol, a compound with strongly hydrophobic properties which reduces inter-particulate interactions and thus limits the AuNP’s tendency to aggregation. 

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