The Return of the CTAB

I started this week trying to successfully clean the free lysine out of my solution of lysine capped citrate gold nanoparticles. My repeated efforts to spin down the nanoparticle complexes without aggregating them proved ultimately futile. But while I was having a battle of wills with my uncooperative nanoparticles I learned that Professor Thompson's lab had finally gotten a new supply of CTAB and had finally landed on a recipe that yielded CTAB gold nanoparticles of the proper size, shape, and concentration for my experiment. So I abandoned the lysine-citrate gold nanoparticle system and went back to my original system. I started by titrating my sheared DNA into the nanoparticles. The resultant UV-vis spectra showed a great deal of aggregation which was surprising.

The next day I made full samples of the 0.1 ug/mL, 1 ug/mL, 10 ug/mL DNA-CTAB AuNPs and measured their UV-vis and DLS against the control. Interestingly, the sample with the smallest concentration of DNA instantly aggregated whereas the solutions with more DNA showed little to no aggregation. The previous titration showed aggregation in all the samples because the severe aggregation caused by the low concentration DNA in the beginning could not be recovered by the addition of more DNA.

In order: Control, 0.1 ug/mL, 1 ug/mL, 10 ug/mL

This phenomenon has been reported before in a paper on DNA electrostatic interaction with DMAP AuNPs and is attributed to lower concentrations not being able to fully cover NPs resulting in a drop in charge that facilitates aggregation (Biver et al.).

Biver, T. et al. “Analysis of 4-Dimethylaminopyridine (DMAP)-Gold Nanoparticles Behaviour in Solution and of Their Interaction with Calf Thymus DNA and Living Cells.” Journal of Nanoparticle Research 14.2 (2012): 1–12. link.springer.com. Web.