Mapping the mesoscale structural landscape using "sculpted" chiral plasmonic fields

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Spectroscopy can detect and characterise the properties of individual molecules through probing quantised states. It is a ubiquitous tool which has been instrumental in many new discoveries over the last 100 years. The applications of spectroscopy are numerous and wide ranging: it allows astronomers to detect water in the atmospheres of planets light years away; and enables art historians to determine the pigments used by old masters in their paintings. Given the unmitigated successes of the spectroscopic method, characterisation of the mesoscale is still one area which remains unconquered. The mesoscale is the intermediate length scale (10-1000 nm) between the molecular (quantum) and the macroscopic (classical) worlds. The length scale is important because it occupies the range over which collective properties begin to dominate those of individual molecules. For instance, it marks the transition from chemistry to biology, when individual molecular building blocks self-assemble into complex biological architectures. Since mesoscale molecular assemblies are effectively classical bodies, there is no quantised state which is representative of the overall structure of the object that can be probed spectroscopically. This limitation of the optical spectroscopic paradigm does have practical implications. For instance, while atomic and molecular pollutants in water and the atmosphere can be readily detected (even monitored in real time) with spectroscopy, detecting and characterising a mesoscale molecular assembly such as an unknown virus can take a significant amounts of time and resource; thus extending time to diagnosis and effective treatment. In this proposal we wish to unlock the shackles of the established optical spectroscopic paradigm by using chiral evanescent electromagnetic fields, rather than light, to rapidly detect and characterise mesoscale molecular structure. When light scatters from chiral plasmonic nanostructures, evanescent EM fields are created in the near field which have a chiral asymmetry (i.e. handedness). In essence the near fields are sculpted by the geometry of the nanostructure, and are imbued with a sense of chirality. The Glasgow Group were the first to demonstrate the existence of these chiral fields, and that they could possess enhanced chiral asymmetry (referred to as superchirality) (Nature Nano 2010). The purpose of this proposal is to show that these superchiral fields can uniquely characterise mesoscale molecular structure, through the use of wild type and synthetic viruses as model systems. To illustrate the potential of the spectroscopy, label free detection of viruses spiked into a biofluid will be demonstrated.