Back in August The Baran Laboratory blog posted some thoughts on yields and the need for qualitative assessment of reactions. I agree with their points, particularly about only believing in “0%, 25%, 50%, 75%, or quantitative” yields.
Unfortunately I can’t recall ever reading a paper on nanoparticle synthesis where the authors report a yield. It is difficult to define the yield of a nanoparticle because, unlike molecules, nanoparticles have a distribution of sizes and shapes which makes the concept of molecular weight and consequently yield somewhat hazy. Still, it’d be useful if chemists reported the mass of dry nanoparticles obtained per batch. Practically, it’s quite straightforward and I think it would be a handy metric for assessing reactions.
Their post inspired me to write some Christmas wishes for the field of nanoparticle synthesis. Here we go:
Reporting centrifugation speeds in relative centrifugal force rather than rotations per minute
Centrifugation is the nanoparticle equivalent of column chromatography. Different size and shape particles sediment at different rates so by centrifuging them you can achieve separation. Typically papers report revolutions per minute (rpm), but the relative centrifugal force (RCF) is a more useful number as it’s this force which causes the particles to sediment at different velocities and separate. RCF is dependent on not just the angular velocity (r, i.e. rpm) but also the radius i of the centrifuge rotor:
RCF = i r^2 / g
where g is acceleration due to gravity. Our centrifuge has the option to set this instead of rpm. As an example, if some authors used a centrifuge at 2000 rpm and then your centrifuge has a rotor with a radius n times larger, the RCF will be n times higher and you’ll need to either reduce the rpm or centrifuging time. But you probably won’t know what rotor they had so you’ll have to guess and waste time working it out for yourself…
Characterisation of what’s been washed away during washing/purification procedures
This is obvious to me but no one does it. If you have to centrifuge, decant the supernatant off the sediment, then wash the product multiple times, what are you getting rid of? I want to know.
Representative electron microscopy
I want big, high resolution images with good contrast. Close ups of particles of interest are fine but I also want to see lower magnification shots showing representative samples of the product. A paper claiming to make nanoparticle X but only one image showing just a few of X? Then I won’t bother trying to reproduce it. Electron microscopy leads me on to…
I love histograms and I want to see them showing size distributions of your product. At least 50 particle measurements, preferably a hundred or more. Rather than simply stating that your product “is monodisperse”, actually give statistical data like the standard deviation to back up your claims. I also like seeing ratios of shape X to shape Y. If you used ImageJ to automatically measure the particles, then include what algorithm and parameters you used so that others can reproduce it.
Papers that do what they claim
If you claim to make nanoparticle X, you should be making at least 75% X by mass. I don’t have a problem with other crud as long as it’s a minority product and you acknowledge that it’s there.
I’d be a very happy boy if I got all of these granted…