In early 2021 I found myself as an early career research fellow with a very limited budget, working in an unfamiliar lab space, with severe restrictions on personal movement in the workspace. No “popping into” someone’s lab to borrow or use equipment. No asking a collaborator nicely for a favour. It was a challenging time to say the least.
I needed to synthesise upconversion nanoparticles (UCNPs), but I didn’t have the high-pressure reaction chambers that are widely used in the research community (price tag pushing £10k which my funding didn’t stretch to) OR the experience necessary to safely perform synthesis at high temperatures under inert atmospheres.
What was I to do?
Well I did a lot of reading around and found a few papers on a little-used technique for creating UCNPs with open-air apparatus at relatively low temperatures by using a polymer, PVP40, as a seeding point and as a growth-limiting template. The only catch? The emission properties of the UCNPs were pretty unremarkable, with relatively weak red emission. The red emission was key, because red light is optimal for biological applications, such as oxygen sensing through tissue.
So… was there a way of making the red emission stronger? Well fortunately quite a few UCNP synthesis papers had shown that Mn2+ doping was beneficial for red emission, but all those studies were performed at high-temperatures or in sealed pressure chambers, and typically started with hexagonal (green emitting) UCNPs changing to cubic (red emitting) UCNPs. I was already making cubic red emitting UCNPs, so was there much point?
There was only one way to find out…. experiment!
Looking back, my twitter timeline reveals that I was quite sceptical of this idea working….
I’m pleased to say that I was wrong and that experiment worked nicely, and I was able to enhance red emission by a factor of ~6, which will make a big difference to how well these UCNPs will function for biomedical imaging.
A typical synthesis produces around about 130 milligrams of UCNPs. Given that UCNPs sell for £261+VAT for 10 milligrams on sigma, each batch has a “street value” of approximately £4000 once 20% VAT is factored in. On a typical day in the lab I was cooking up two batches, so around about £8000 worth of product…
I really hope that this method proves to be useful to researchers around the world. I know there any many people interested in UCNPs who won’t have the resources or chemical expertise to use the more conventional methods and I am curious to see where others will take it.
Myself, I’m currently playing about with adding mesoporous silica shells to these PVP coated UCNPs… watch this space!
P.S. I am also very happy that this is the first proper “nugget” of research from my BBSRC Discovery Fellowship.
