One of my favourite things about being a scientist is the knowledge that one day you may be part of something that changes the world! Unfortunately, this change can be for the better or worse – and often the ‘worse’ is what makes a better story! This is why we get books like Michael Crichton’s ‘Prey’ – a book centred around the so called “Grey Goo” hypothesis of nanomachines. If you’re not familiar with “Grey Goo”, it’s the idea that self-replicating nanomachines could take over the world and devour all carbon-based life in a matter of days, leaving our planet a barren wasteland. The term and idea is attributed to nanotechnologist Eric Drexler from his book “Engines of Creation” and the name was intended to indicate that something visually unintestesting, could potentially outcompete the diversity of life that evolution creates with relative ease given the ideal conditions. Before I give this idea too much credence I should probably state that the Royal Society, at the directive of Prince Charles, published a report on the possibility of this occurring in 2004 and dismissed it as impossible – so try not to worry about it too much! I should probably point out that limitless replication is the LAST thing that you would ever want most nanomachines to do, as even naturally occurring ones (yes there are far more naturally occurring nanomachines than man-made nanomachines) exist primarily for one specific function, and so producing billions of copies of them is hugely inefficient! In fact ‘ideal’ nanomachines – in a biological sense at least – perform their function whilst having as few nanomachines present as possible. It’s just like the catalytic efficiency of an enzyme in biology – ‘better’ enzymes are those that do the same thing but require less inputs!
The final comment in the “Grey Goo” scenario is that technologically – we’re not on the same page as infinitely replicating nanomachines. We’re not even reading the same book! By way of an example, a paper published in the ‘Nano Letters’ journal earlier this year , showcases one of the most advanced and coolest examples of a functional, synthetic nanomachine that I have stumbled across so far!
The above image shows a diagrammatic image of the nanomachine in question. It looks like a little torpedo doesn’t it? The paper authors describe these as ‘microrockets’ and they’re made photolithographically (i.e. light is used to etch a pattern into a silicon wafer in a process similar to how computer transistors are made). From there they are covered in gold, mercaptohexanol and a specific ‘capture’ DNA sequence which allows the rockets to ‘pick up’ strands of RNA or DNA via complementary base pairing. If you’re wondering why you need gold and mercaptohexanol (as I did!) the gold helps the ‘capture’ DNA sequence to stick to the rocket and the mercaptohexanol prevents non-complementary DNA from sticking to the rocket (like a non-stick coating on a frying pan).
So why bother? Well for starters DNA detection is big business and used in various industries all over the world, but there is a problem with it. Specifically, biological systems are messy (see image above) and contain all sorts of junk as well as the DNA that you want to detect. So usually you have to go through a long, expensive purification process before you can actually detect or isolate DNA from any biological samples. What this group showed is that by adding some ‘fuel’ for the mircorockets to the biological sample (in this case it was peroxide and sodium cholate), these rockets will actually propel themselves forward like a torpedo, even in really messy biological systems. What the diagram above show is that this propulsion can be used to drag the ‘captured’ DNA along with the rocket down a microchannel to a purified region where it can be quickly, cheaply and easily isolated or detected. This has immense implications for any technology involving DNA and I can’t wait to see what more innovation come after this! Oh and also it’s really, REALLY cool!
1) D. Kagan et al “Functionalised Micromachines for Selective and Rapid Isolation of Nucleic Acid Targets from Complex Samples” Nano letters 11, 2083-2087 (2011) doi:10.1021/nl2005687