Metal nanoparticles, when assembled into higher order nanostructures, exhibit unusual optical properties which lend themselves to exciting applications for society such as plasmon-enhanced solar light harvesting (e.g. for solar cells), ultrasensitive chemical and biological sensing (e.g. for early detection of diseases), photocatalysis and optical circuitry (e.g. for faster communication). The remarkable optical properties of nanoparticles that give rise to these applications are dependent on nanoparticle size and shape, but are mostly governed by the spacing between nanoparticles. Whilst synthetic routes for controlling nanoparticle size and shape have dramatically improved during the past two decades, the development of methods for controlling inter-particle spacing has remained a fundamental scientific challenge.
Cucurbiturils (CB[n]s) are a family of barrel-shaped molecules. To date, CB[n]s with n=5-10, have been isolated and characterised. Prof. Scherman and Prof. Baumberg have previously demonstrated that CB[n] macrocycles can be utilised in producing photonic nanoarchitectures, forming rigid linkers between the nanoparticles providing accurate interparticle spacings of 0.9 nm (the thickness of a CB[n] molecule). Spacings of 0.9 nm are within the `close-coupling regime’ for plasmonic structures, where focussing of the incident electromagnetic radiation between nanoparticles is most intense (termed `hot-spots’). Moreover, these molecules are capable of accepting guest molecules into their internal cavity. While CB[5]-CB[7] can accommodate one guest, the larger homologue CB[8] can even accommodate two guests. This is an extremely useful trait for ultrasensitive sensing (detecting and studying molecules).
Nanoparticles and assembled nanostructures show promise in a wide variety of applications, but their uptake into current technologies has stalled due to the difficulty of their production and manipulation post-assembly. Therefore, new routes to readily control the assembly of nanoparticles represent an important area of research. I utilise the unique macrocyclic host-guest chemistry of CB[n]s in conjunction with gold nanoparticles to demonstrate a novel approaches to nanoparticle self-assembly. The aim of this action was to produce new gold nanoparticle structures to be used as constructs for Surface-Enhanced Raman Scattering (SERS), which is a sensitive light detection technique for molecules, to obtain (1) fundamental insights into SERS (2) perform and study (catalysed) chemical reactions, and (3) perform advanced molecular sensing, meaning detecting molecules at very low concentrations or detecting properties of molecules that were previously not accessible. Achieving these objectives opens up new avenues for the applications mentioned. Overall, the objectives of this action were nearly all achieved and most surpassed, with some objectives reached via unforeseen pathways.
