Somehow this never occurred to me before, but nanoparticles don’t have to be made from metals or other inorganics. They can even be biodegradable. It’s something you tend to forget when you keep reading papers about how metal oxide nanoparticles penetrate cells and catalyze the formation of free radicals or whatever.
But of course there is always the option of creating nano-sized chunks of common polymers. The major drawback is that they don’t have as interesting physical properties of inorganic particles, with all those size-depending effects and abundant catalytically active sites. They are, in short, a lot less interesting than their inorganic counterparts and that’s why you rarely hear about them.
Are organic nanoparticles useful at all, then? There seems to be some hope for them, at least that’s what I took home from a current paper in Nano Letters. Scientists apparently plan to incorporate pharmaceuticals in these polymer nanoparticles to facilitate their slow or controlled release. Stanford Chemists now found a very simple and straightforward procedure to create these loaded nanoparticles from the biodegradable polymer chitosan.
Image from publication abstract, see here.
As you can see, the apparatus rather looks like something you would expect to find in a school lab. It is essentially a U-shaped tube with a nanoporous membrane of some sort dividing both halves of the apparatus. One half contains a solution of chitosan at pH 3, where the polymer is soluble, while the other half contains a sodium hydroxide solution at pH 11. As separating membrane the researcher used track-etched polycarbonate with a pore diameter of 10 nanometer and a nanoporous anodized aluminium oxide membrane with a pore diameter of 20 nanometer.
When the chitosan solution is pushed through the membrane – which is achieved by simply filling more liquid in that side of the U than in the other – the chitosan precipitates in the high-pH-solution and forms nanoparticles of sizes roughly dependent of the pore diameter. When the researchers added rhodamin 6G to the chitosan solution, the molecule ended up incorporated into the particles – it seems at least likely that this might work with other, more useful molecules, too.
All this is hardly awe-inspiring. I rather like the simplicity of the apparatus and the fact that I never before heard about this line of research. In all fairness, this has at least some potential. There are many parameters that influence the outcome of the procedure, and the authors mention that they also obtained hollow nanotubes and nanowires at higher flow rates. So you never know what may come out of this.
Guo, P., Martin, C., Zhao, Y., Ge, J., & Zare, R. (2010). General Method for Producing Organic Nanoparticles Using Nanoporous Membranes Nano Letters DOI: 10.1021/nl101057d