Abstract
Surface properties of gold nanoparticles (Au-NPs) can be easily modified with self assembled monolayers (SAM). This is extremely relevant for cancer detection and treatment. But for such applications, it's important to characterize these nanoparticles from the perspective of purity, monodispersity, strength and stability of SAM bindings. Firstly, we demonstrate the use of electrospray-differential mobility analysis (ES-DMA) for characterizing non-functionalized and functionalized 10 to 60 nm citrate stabilized Au - colloids which enable us to determine the packing density. We also carry out temperature programmed desorption (TPD) of the bindings and find the binding energy to be consistent with studies of SAMs on flat surfaces. Lastly, we demonstrate ES-DMA's utility to investigate nanoparticle flocculation. By tuning in the ionic strength of the Au colloid solutions we are able to track the fraction of each aggregate species as a function of time which then enables us to determine extent of aggregation, aggregation rate and stability ratio at different ionic strengths. This demonstrates that ES-DMA is a valuable tool for quantitatively probing early stages of colloidal aggregation and can also be used as a size selection tool for studying specific aggregates. © 2010 Springer-Verlag.