The sadly predictable hyping of things nano reached a nadir recently with the promotion of silver nanoparticles (aka “silver bullet”) as a treatment for ebola virus. There has been a great discussion of this and other aspects of silver nanoparticles by Andrew Maynard (here, here for ebola and here for the essential Risk Bites video).
It may surprise some, but until a few weeks ago, there was no simple, direct published method to quantify non-destructively silver nanoparticles. Yet, the non-destructive quantification of silver nanoparticles is essential to any experiment that aims to prepare and use these in a biological context. Without it any experimental work is likely to be qualitative and simple things, such as determining the stoichiometry of functonalisation, become difficult. Indeed, so important is simple quantification of nanoparticles that we validated and published a method for gold nanoparticles in 2007 that has been very well received by the community and which we use daily in the lab.
A few weeks ago all this changed, when Paul Free in Singapore published a method in The Analyst entitled A rapid method to estimate the concentration of citrate capped silver nanoparticles from UV-visible light spectra to quantify silver nanoparticles by uv-vis spectrometry. Like the previous work on gold, it is based on Mie theory. The present work on silver uses an elegant bit of lateral thinking by Paul Free, which allowed him to measure the amount of silver using the product of a reaction with cyanide and a cyanide ion selective electrode, a critical step in the work. Multiple experimental validations using different techniques and theory round off what I think will prove to be a most useful paper for the field – it works, it is simple, all you need is a uv-vis spectrometer and knowledge of the diameter of the silver nanoparticles and you can figure out the concentration.
After pulling the wrong lottery ticket at publisher X, the paper has found a happy home at The Analyst, a publication of the Royal Society of Chemistry. Such a happy home that the RSC decided this was to be one of their “HOT” papers, though this appellation always brings images of charred pages and the end of civilisation to my mind!
I wanted to go Open Access, but the Singapore team were constrained by budget and the antediluvian practice of using impact factor as part of the metric for determining career progression there. Nonetheless, the paper will be available in due course in the A*STAR and University of Liverpool repositories and in the meantime a short e-mail to any of the authors will guarantee a PDF by return – the electronic equivalent of a “request-a-print” in the days of paper and snail mail, but a lot faster.
I hope that now we will see an increase in quantitative experiments in biology with silver nanoparticles. Despite the hype, they do have really interesting properties. They release Ag+ ions, which are toxic to bacteria and perhaps some viruses (see links to Andrew Maynard’s musings on the subject), and they have a much stronger photoactivity compared to gold, so an interesting material to work with.
Update 22 August 2014
Paul has placed the pre-publication PDF at Research Gate. This does look useful and though I have resisted (resisted makes it look like a conscious decision, it is more a question of activation energy/inertia/procrastination…) it looks like I should invest some time and put my closed access papers up there.