Towards Intelligent Autonomous Nanoswimmers.

This work will combine two clearly defined and characterised physical effects, self-diffusiophoretic nanoswimmers (self- propelled nanoparticles) and pH-responsive hydrogels, to produce a new class of nanoswimmers which are able to swim towards a chemically identified target, mimicking the behaviour of living cells. It will demonstrate for the first time a wholly synthetic version of chemotaxis and will be one of the key building blocks for the soft nanotechnology devices to come, whilst acting as a very simple biomimetic model allowing insight into cell chemotaxis behaviour.The media often presents the image of nanotechnology as a miniaturised submarine navigating through the arteries and veins of the human body. Closer inspections of the physical laws at such dimensions mean the idea of the nanoscale submarine gliding through the body, should be replaced with it struggling through a treacle-like liquid while being constantly hit by nanoscale cannon balls. At the nanoscale water behaves like treacle and a collision with even a single water molecule has an effect.In nature many organisms are able to swim through this nanoscale environment with great success. Bacteria, such as E.Coli, have a corkscrew-like tail which it rotates to push itself through the treacle-like water. In searching for food, they adopt a run and tumble strategy where long runs of straight motion are interrupted by tumbling event where it stops, rotates and then begins to run in a new direction. If this direction is unfavourable it stops, rotates, and runs again.A simple method for producing an synthetic propulsive effect at the nanoscale is to make use of chemical reactions taking place on the surface of a nanoswimmer, such as a spherical particle half coated with a catalyst. Given the right chemical fuel the catalyst will break down the fuel to produce a localised cloud of reaction products which generates a propulsive force on the sphere. However, there is no control over the direction in which they swim.Collisions with the surrounding liquid molecules not only kicks particles it also spins them. It is this spin which causes propelled particles to swim in a random fashion. However, the speed at which it spins is related to its size. The larger the object, the slower it rotates.This research project will develop a new class of nanoswimmers that are able to both propel and steer autonomously. They will be based upon previously successful nanoswimmers possessing a half coated catalyst surface that are able to physically change shape in response to a chemical signal. If the nanoswimmer swims towards a favourable chemical signal, i.e. an acid, it will expand. By doing so, its speed of rotation will be significantly reduced and it will then be able to continue to swim towards the chemical signal. More specifically, microspheres will be produced using the proven technique of electrospraying, where one half of the microsphere will contain the platinum catalyst. This will be the propulsive part of the sphere. The remaining half of the sphere will be made from a pH-responsive polyelectrolyte hydrogel. This material expands and collapses depending upon the pH of the surrounding solution. This volume transition, and hence change in rotational behaviour, will be used to determine the direction in which the nanoswimmer propels itself. It is also possible to have polymer gels which demonstrate a volume change in response to glucose. These will be used to investigate swimmer that steer towards high concentrations of glucose.This exciting research project will be undertaken by a PDRA who will benefit from working and training in such a stimulating and adventurous research area. This grant will form the springboard for future research grant applications and research avenues both theoretically and experimentally, whilst also highlighting the interdisciplinary nature of this project and nanotechnology as a whole.