Programmable nano-assembly of plasmonic materials for molecular interactions

The ability to look at small numbers of molecules in a sea of others has appealed to scientists for years. On the fundamental side we want to watch in real time how molecules undergo chemical reactions directly, how they explore the different ways they can come together, interact and eventually form a bond, and ideally we would like to influence this so that we can select just a single product of interest. We also want to understand how molecules react at surfaces since this forms the basis of catalysis in industrially relevant processes and is thus at the heart of almost every product in our lives. However, most scientific studies take place in precise conditions achieved in the laboratory, such as high vacuum, to select the cleanest possible conditions, but which look nothing like the real world applications they simulate. Hence most knowledge is empirical and pragmatically optimised.

We have been working on a completely new way to watch chemistry in an incredibly tiny test tube, itself a molecule. We use a barrel-shaped molecule called a 'CB' that can selectively suck in all sorts of different molecules. Recently, we have found a way to combine these barrel containers with tiny chunks of gold a few hundred atoms across, in such a way that shining light onto this gold-barrel mixture focuses and enhances the light waves into tiny volumes of space exactly where the molecules are located. By looking at the colours of the scattered light, we can work out what molecules are present and what they are doing, with enough sensitivity to resolve tiny numbers.

Our aim in this grant is to explore our promising start (that was seeded by EU funding). We aim to develop all sorts of ways to make useful structures that sense neurotransmitters from the brain, protein incompatibilities between mother and foetus, watch hydrogenation of molecules take place, find trace gases that are dangerous, and many others. At the same time we want to understand much more deeply and carefully how we can go further with such ideas, from controlling chemical reactions happening inside the container, to making captured molecules inside flex which can result in colour-changing switches. To make all this happen we take research groups spanning physics and chemistry and completely mix them up, so that they can work together on these very interdisciplinary aspects. We have found this works extremely well. We also involve a number of companies and potential end users (including the NHS) who know the real problems when trying to exploit these technologies in important areas including diagnostics, imaging and catalysis.

We believe that a large range of potential impacts will emerge from this research programme:

Fundamental:
Understanding and controlling self-assembly on the sub-nm size scales has been sought for many years. We believe we have found a robust and significant approach, and that many further developments will emerge from our research. In particular demonstrating the influence of quantum transport within the optical domain is a real opportunity, as well as controlling electronic transport (since we create many identical junctions). We believe our approach will influence a wider research community to take up our ideas and develop them further in many directions.
Secondly, watching molecular interactions directly on this size scale opens up very many new possibilities in chemistry. Again we believe that there are prospects for others taking our advances in many directions. For instance exploring how conduction through molecules sequestered in the CBs between Au NPs offers a new route to molecular electronics. We have indicated in the proposal many promising areas around molecular sensing, and the potential control of chemical reactions, but we believe many more areas are possible. Because CBs are inert, and synthesised in high yield and volume, there are real practical applications that can follow.

Users:
The biomedical community would be strongly impacted for using this in real-time high-sensitivity biomolecule sensing. This is already evidenced by direct involvement of the NHS Raman Unit in this grant, as well as Renishaw Diagnostics who sell plasmonic diagnostics to this community (as well as the biomedical research and pharmaceutical sector). The ability for low-cost rapid medical screening would make a major impact to health.

The industrial and security communities would be impacted, for real-time sensing of molecules in a wide variety of scenarious. Evidence by direct involvement of BP in assembling sensors and catalyst probes, and DSTL for pathogen detection. The police have long sought a roadside test for cannabis (approaching us several times), while there are a host of applications in trace gas and contaminant detection.

Public:
We will all benefit from improved high-sensitivity, robust and quantitative sensing capabilities for molecular detection, leading to advances in mass-scale health screening, environmental sensing, security, and improved chemical products. More distant goals include advances in catalysis, including carbon sequestation. The public will also benefit from our novel ways to see quantum mechanics in action in ambient conditions, for instance at the science outreach events we plan.

More detailed impact consideration can be found in our Impact statement.