One of the buzz words used in news reports of chemistry is the prefix “nano-“. As an organic chemist of over fifteen years experience, I really don’t like the word “nano” anymore. It’s simply been overused, and has lost much of it’s original meaning. It’s origins can be found in the S.I. measurement system, which assigns powers of ten various prefixes. A kilometer, for example, is 1×10^3 meters or 1000 meters. A centimeter is 1×10^-2 meters, or 0.01 meters. Nano is used for the 10^-9 component, so a nanometer is very small indeed – 0.000000001 meters. It’s on the same scale as atoms and molecules. One chemical bond might be a few Angstroms, or tenths of a nanometer, long. A decently sized molecule is therefore a handful of nanometers in size. Therefore, the phrases “nanoscience”, “nanochemistry”, and “nanoengineering” aren’t really adding anything to the discussion; it’s understood that chemistry takes place on the nanoscale.
Perhaps the worst offender in the list of nano-words is “nanomachine”, also known as “nanobots”. As a professional chemist, that word really irks me. It makes for a nice image, and there have been several popular books written on the subject, but there is a central difficulty with these nanomachines that many people overlook. Imagine that you’re asked to tighten a screw with a screwdriver. Most of us are probably capable of that. Now, imagine it’s a tiny screw – maybe one of those you see in eyeglass repair kits. You have to use a tiny screwdriver. Now, imagine that the screw is millions of times smaller than that – a nanoscrew. You can’t see it anymore, and trying to access it with some sort of nanoscrewdriver is all but impossible. Tiny fluctuations of air currents at the surface scatter the screws to the winds, and even the small static charges present on everyday materials can jolt the machines out of alignment.
I’m aware of the excitement behind nanobots, just as much as I’m aware of the problems. I like to study the field but I’m realistic about the difficulties. Trying to separate popularistic fantasies (nanocars, molecular robots) from the real science being done can be difficult at times. Thankfully, I came across a wonderful article in the prestigious journal Nature: Chemistry which outlines work being done on fused aromatics. The article details how these molecules, which are shaped like flat discs and diamonds, can be made to lie down on a surface in a controllable fashion. Fused aromatics are hexagons which share a common edge, sort of like a fragment of a hexagonal grid map. They are stiff and flat, and possess a defined shape that doesn’t easily deform. You can imagine taking a handful of these molecules and arranging them on a surface so that all of the pieces lined up, like a jigsaw puzzle. That’s the type of control you would need in order to make these nanoscale molecules approach anything like a machine behavior.
The chemists behind the study describe how the most important factor in the pattern formed by the molecules was the small fluctuations in the starting conditions. In the macroscopic world, we’re used to wide ranges of acceptable values. We’re happy driving between 30 and 70 miles per hour, we can drink 6-12 glasses of water a day for extended periods, and so forth. Because of their tiny size and the electrostatic charges which have influence at the nanoscale, the fused aromatics in the study were found to have much sharper ranges of acceptable surrounding conditions. Even small variations led to widely varying tile patterns on the surface. It’s refreshing to read an article such as this, because it really takes the wind out of the popular media depictions of “nanorobots” even as it begins to outline the true science behind the field.
The source of this article can be found at:
Stannard, A., et al. “Broken symmetry and the variation of critical properties on the phase behavior of supramolecular rhombus tiling”. Nature: Chemistry, 2011, 4, 112-117.