‘Theranostics’ – Therapeutic Diagnostics

By Elf Eldridge 30/12/2011


Theranostics, this odd combination of ‘therapeutics’ and ‘diagnostics’, describes a simultaneous diagnosis and treatment for a disease. One can imagine this in the form of existing compounds that are known to accumulate in tumor cells, thus allowing them to be tagged (radioactively or flourescently) to enable diagnosis and can also be functionalised with anti-tumor agents that inhibit tumor growth at the same time. Aimee and I discussed this several weeks ago on TOSP 14, where a 17 year old was able to create a nanoparticle capable of both releasing a drug that targets cancer stem cells and functionalizing the nanoparticle with gold and iron nanoparticles to allow its study using MRIs or optical diagnostic techniques. However, a new paper published in the Nano Letters journal in December 2011 has shown an entirely novel way to achieve a similar effect by using nanomotors to purify, detect and then potentially treat bacteria such as E.coli in a range of solutions.

Metallic Microengine (yellow) with attached bacteria (E.coli = green) driven by bubbles
Metallic Microengine (yellow) with attached bacteria (E.coli = green) driven by bubbles. From Reference 1.

So looking at this little nanomachine step-by-step, each part has been designed with a specific purpose in mind. Firstly the nanomotor itself, whilst not ‘true’ nanotechnology as it’s about 8 microns long (about the same size as a red blood cell), it still pretty amazing. They’re (relative to other microengines) cheap and easy to manufacture, and propel themselves froward, like torpedoes, through a liquid by shooting bubbles out behind them. The bubbles themselves are created within the cylinder, where a layer of Platinum catalyses the conversion of the hydrogen peroxide ‘fuel’ to oxygen, forming bubbles that are then ejected out the rear of the engine, propelling it forward.  The second step is adding a ‘binding domain’ (imagine the nano-equivalent of a fishing net) to the back of the motor. This fishing net is a little special though as it ONLY catches a certain type of bacteria, namely Gram-negative bacteria, and is unable to catch things like yeast, other forms of bacteria or other nanoparticles, making it excellent for purification. That said, there is only a little chemistry needed to swap this specificity for other things, such as those listed above.

Figure showing the capture and subsequent release of E.coli bacteria by the microengine via a simple change in pH
Figure showing the capture and subsequent release of E.coli bacteria by the microengine via a simple change in pH. From Reference 1.

The third step is a release mechanism. Once the target bacteria has been captured, the microengine allows it to be towed to a specific location and then released again by a simple change in pH. Now these little micromachines are acting as nano-couriers, delivering their cargo to wherever you desire. And the final step is to add a second fishing net, capable of catching anti-bacterial drug particles. The idea here is to bring the bacteria into close physical contact with the drug, increasing the chance that the drug will have impact the growth of the bacteria, killing it or slowing it down more effectively than current treatments that essentially bathe the bacteria in toxins in order to kill them which can lead to many of the unpleasant side effects (for example those associated with anti-TB drugs).

So, in summary, some seriously cool technology. However, it’s the implications of this that really staggers me. This technique allows you to isolate bacteria from complex samples (i.e. blood or urine) in real time with high sensitivity whilst SIMULTANEOUSLY treating the infection. This is the sort of nanotechnology fantasy Eric Drexler envisioned.

References:

1) S.Campuzano et. al “Bacterial Isolation by Lectin-Modified Microengines” Nano Letters,

doi:10.1021/nl203717q