Looking for a change?
They say that only two things I life are certain, death and taxes. I’d add that a third is change. Let’s be honest nothing really stays the same, even if we’d like it to. Our own existence is based on things staying constant, but that doesn’t mean that our own bodies aren’t changing, but rather are in a dynamic equilibrium, constantly updating and making small changes to maintain the status quo, a curious but essential state of affairs no?
Frequently, I meet people who want to understand a material or system that either should remain the same but won’t or who would like to engineer a system that changes by design. Both are candidates for a revolution in electron microscopy that has been on the rise over the past few years – dynamic or in situ microscopy. I know that there will be those of you to whom this is definitely not news, but indulge me as I offer help to those who perhaps are less enlightened.
Let’s go back a few years into EM history. Imagine you want to have a deeper understanding of your colloid or nanoparticle system and understand what happens over, let’s say an hour of its lifetime. The chances are that if you’re looking on a transmission electron microscope (TEM) then you’re going to need to deposit the solution (or multiple samples over the time period of interest, for 60 minutes) onto a copper grid (other options are available) and let it dry. You may be fortunate to have a cryo-holder and freeze your time lapse samples to avoid drying and dehydration artefacts, you might do this for 3 or 4 time points over an hour, after which you typically notice the system has changed significantly changed. The grids can be imaged and a series of images acquired. The next challenge is to make sense of what might have changed between samples / time points. This could be pretty tricky, imagine that you’re watching a film and effectively guessing what’s happened between you covering and uncovering your eyes every 15 minutes over a 90 minute film. The chances are that you’d have a vague idea of start, middle and end, but not many details of the way in which the main scenes fit together. To take another microscopy example, you might be interested the development of a strengthening precipitate in an alloy. You start with a typical base material and then compare with a second and third treated material. Again, you’re looking at the samples trying to infer what’s changed from observation A to B and assuming that certain things have or haven’t happened, but you’re essentially making an educated guess!.
Some years ago I became aware that there were people who were not willing to accept this scientific guesswork with their samples, rather they were developing hardware that could allow samples to be heated or electrically stimulated in the microscope. This uptake in in situ microscopy has growing steadily in the past 5 years, but early pioneers such as Pratiba Gai will point out it typically meant potential ruin of your electron microscope if it all went wrong. I recall seeing examples of ETEM (Environmental TEM) in 2006 and being blown away that it was possible – that is to say, pumping in gasses such as hydrogen into the controlled vacuum of a TEM, whilst heating the sample, to observe the reaction as it would be in a traditional reaction vessel. Now, not everyone has a microscope they can go drilling holes in the side of, or buy one of the now commercially available microscopes, and so other inventive people have developed systems to permit reactions (heating and reactive gasses) or indeed liquid samples to be maintained or reacted, all confined within a thin electron transparent cell. This has been made possible more recently through the use of MEMS based systems from supplier such as (in alphabetical order) DENS Solutions, Hummingbird Scientific or Protochips.
The good news doesn’t stop there, SEM gets a look in too, with stages developed to permit the observation of samples while measuring strain or compression, or whilst heating, or cooling a sample. Courtesy of environmental (ESEM) or variable pressure (VP-SEM) it is possible to observe and understand samples with a high water content, such as cells or colloids.
All of this is exciting, however, there is a price to pay. The hardware is pretty specialist and therefore costly and I’d assume many could be priced out from entering the world of in situ rather accepting that the traditional static microscopy is good enough. The other price to pay can be an observable reduction in clarity or resolution of images, or an observable damage of the sample due to the interaction of the electron beam with solvent, gasses or the sample itself. The question, I suppose you have to ask might be, ‘is it worth it, if it adds to your understanding or actually seeing your system ‘live’?’
Of course light microscopists are probably sitting reading this and smiling. Free from the restriction of operating in vacuum or having a highly energetic irradiating beam they’re used to watching a sample for long periods of time as it changes. My favourite application of this is light sheet microscopy, from which many beautiful movies have been generated over days in some cases as an embryo is observed developing second by second. There has been a move toward using lower intensity of light, especially imaging cells which can be very sensitive to radiation (light is after all still radiation) and using very short pulses of light, illuminating only a thin layer of the sample at a time. In fact, Nobel laureate Eric Betzig, not content with having developed super-resolution microscopy, has been working on ways to use, ever tinier, weaker and shorter pulses of light to observe cells more rapidly, while protecting the cells. Phillip Laissue has also working to make low light microscopes for the observation of coral.
All things considered, we’re on the brink of a turning point (another change) in the way we plan and conduct experiments, both in the way we prepare samples free from artefact and observe them in real-time and real environment (whatever that may be), but being able to observe any change.
Until next time