Determining Nanoparticle Concentration

Back in March, I found a communication in JACS about determining the concentration of quantum dot nanoparticles by measuring their fluorescence burst counts by the Johnson group at York College. The QD solution (which could be in aqueous or organic solvent) was passed through a laser to induce the excitement and the different wavelengths emitted were separated by dichroic mirrors. The scheme is shown below.



They refer to this as a simple and accurate process. They do get good results, so I will give them accurate, but simple? I suppose if you work in lab that does a lot of laser chemistry, this might be simple, but not for me. Regardless, I don't think the method has that much going for it. There are other ways in which you can determine nanoparticle concentration, and other information about your system simultaneously. The one cool thing that this method does have going for it is that if you have a mixture of quantum dots that fluoresce at different wavelengths, you can measure both of their concentrations simultaneously.

However, back in 2004, there was a review in Accounts of Chemical Research, on using a carbon nanotube system to quantify nanoparticle concentration, by the Crooks group at Texas A&M. I wouldn't describe this as a simple system either, however. It involves embedding a carbon nanotube in an epoxy matrix, and creating an electrochemical system where the nanoparticles move by electrophoresis. A schematic is shown below.



The nanoparticles pass through the carbon nanotube, which has an ionic current passing through it. Based on the frequency and pulse height of the change due to the nanoparticle, they were able to obtain the concentration and nanoparticle size respectively. This has many advantages over the previous system. Firstly, the nanoparticles don't have to be quantum dots, non-fluorescing nanoparticles can be measured as well. Additionally, the nanoparticle size is being measured. This method is known as a Coulter counter.

These systems both have their pluses, but as you can tell, I prefer the carbon nanotube based system.

Zhang, C., Johnson, L. (2008). Simple and Accurate Quantification of Quantum Dots via Single-Particle Counting. Journal of the American Chemical Society, 130(12), 3750-3751. DOI: 10.1021/ja711493q

Ito, T., Henriquez, R.R., Crooks, R.M. (2004). A Carbon Nanotube-Based Coulter Nanoparticle Counter. Accounts of Chemical Research, 37(12), 937-945. DOI: 10.1021/ar040108+

Godspeed.



This posted tagged as: journals, science

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