Proposed model of the Dictyostelium cAMP receptors bound to cAMP.

3',5'-cyclic adenosine monophosphate (cAMP) is well known as a ubiquitous intracellular messenger regulating a diverse array of cellular processes. However, for a group of social amoebae or Dictyostelia undergoing starvation, intracellular cAMP is secreted in a pulsatile manner to their exterior. This then uniquely acts as a first messenger, triggering aggregation of the starving amoebae followed by their developmental progression towards multicellular fruiting bodies formation. Such developmental signalling for extracellularly-acting cAMP is well studied in the popular dictyostelid, Dictyostelium discoideum, and is mediated by a distinct family ('class E') of G protein-coupled receptors (GPCRs) collectively designated as the cAMP receptors (cARs). Whilst the biochemical aspects of these receptors are well characterised, little is known about their overall 3D architecture and structural basis for cAMP recognition and subtype-dependent changes in binding affinity. Using a ligand docking-guided homology modelling approach, we hereby present for the first time, plausible models of active forms of the cARs from D. discoideum. Our models highlight some structural features that may underlie the differential affinities of cAR isoforms for cAMP binding and also suggest few residues that may play important roles for the activation mechanism of this GPCR family.

Biomacromolecular Stereostructure Mediates Mode Hybridization in Chiral Plasmonic Nanostructures.

The refractive index sensitivity of plasmonic fields has been exploited for over 20 years in analytical technologies. While this sensitivity can be used to achieve attomole detection levels, they are in essence binary measurements that sense the presence/absence of a predetermined analyte. Using plasmonic fields, not to sense effective refractive indices but to provide more "granular" information about the structural characteristics of a medium, provides a more information rich output, which affords opportunities to create new powerful and flexible sensing technologies not limited by the need to synthesize chemical recognition elements. Here we report a new plasmonic phenomenon that is sensitive to the biomacromolecular structure without relying on measuring effective refractive indices. Chiral biomaterials mediate the hybridization of electric and magnetic modes of a chiral solid-inverse plasmonic structure, resulting in a measurable change in both reflectivity and chiroptical properties. The phenomenon originates from the electric-dipole-magnetic-dipole response of the biomaterial and is hence sensitive to biomacromolecular secondary structure providing unique fingerprints of α-helical, ß-sheet, and disordered motifs. The phenomenon can be observed for subchiral plasmonic fields (i.e., fields with a lower chiral asymmetry than circularly polarized light) hence lifting constraints to engineer structures that produce fields with enhanced chirality, thus providing greater flexibility in nanostructure design. To demonstrate the efficacy of the phenomenon, we have detected and characterized picogram quantities of simple model helical biopolymers and more complex real proteins.

Spatial control of chemical processes on nanostructures through nano-localized water heating.

Optimal performance of nanophotonic devices, including sensors and solar cells, requires maximizing the interaction between light and matter. This efficiency is optimized when active moieties are localized in areas where electromagnetic (EM) fields are confined. Confinement of matter in these 'hotspots' has previously been accomplished through inefficient 'top-down' methods. Here we report a rapid 'bottom-up' approach to functionalize selective regions of plasmonic nanostructures that uses nano-localized heating of the surrounding water induced by pulsed laser irradiation. This localized heating is exploited in a chemical protection/deprotection strategy to allow selective regions of a nanostructure to be chemically modified. As an exemplar, we use the strategy to enhance the biosensing capabilities of a chiral plasmonic substrate. This novel spatially selective functionalization strategy provides new opportunities for efficient high-throughput control of chemistry on the nanoscale over macroscopic areas for device fabrication.

Disposable Plasmonics: Plastic Templated Plasmonic Metamaterials with Tunable Chirality.

Development of low-cost disposable plasmonic substrates is vital for the applicability of plasmonic sensing. Such devices can be made using injection-molded templates to create plasmonic films. The elements of these plasmonic films are hybrid nanostructures composed of inverse and solid structures. Tuning the modal coupling between the two allows optimization of the optical properties for nanophotonic applications.

The origin of off-resonance non-linear optical activity of a gold chiral nanomaterial.

We demonstrate that engineered artificial gold chiral nanostructures display significant levels of non-linear optical activity even without plasmonic enhancement. Our work suggests that although plasmonic excitation enhances the intensity of second harmonic emission it is not a prerequisite for significant non-linear (second harmonic) optical activity. It is also shown that the non-linear optical activities of both the chiral nanostructures and simple chiral molecules on surfaces have a common origin, namely pure electric dipole excitation. This is a surprising observation given the significant difference in length scales, three orders of magnitude, between the nanostructures and simple chiral molecules. Intuitively, given that the dimensions of the nanostructures are comparable to the wavelength of visible light, one would expect non-localised higher multipole excitation (e.g. electric quadrupole and magnetic dipole) to make the dominant contribution to non-linear optical activity. This study provides experimental evidence that the electric dipole origin of non-linear optical activity is a generic phenomenon which is not limited to sub-wavelength molecules and assemblies. Our work suggests that viewing non-plasmonic nanostructures as "meta-molecules" could be useful for rationally designing substrates for optimal non-linear optical activity.