The spectroscopic analysis of large biomolecules is important in applications such as biomedical diagnostics and pathogen detection 1,2 , and spectroscopic techniques can detect such molecules at the nanogram level or lower. However, spectroscopic techniques have not been able to probe the structure of large biomolecules with similar levels of sensitivity. Here we show that superchiral electromagnetic fields 3 , generated by the optical excitation of plasmonic planar chiral metamaterials 4,5 , are highly sensitive probes of chiral supramolecular structure. The differences in the effective refractive indices of chiral samples exposed to left-and right-handed superchiral fields are found to be up to 10 6 times greater than that those observed in optical polarimetry measurements, thus allowing picogram quantities of adsorbed molecules to be characterised. The largest differences are observed for biomolecules that possess chiral planar 2 sheets, such as proteins with high β-sheet content, which suggest that this approach could form the basis for assaying technologies capable of detecting amyloid diseases and certain types of viruses.Since the building blocks of life are chiral molecular units such as amino acids and sugars, biomacromolecules formed from these units also exhibit chirality on molecular and supramolecular scales. Chirally sensitive (chiroptical) spectroscopic techniques, such as circular dichroism (CD), optical rotatory dispersion (ORD) and Raman optical activity (ROA), are therefore especially incisive probes of the threedimensional aspects of biomacromolecular structure and are widely used in biomolecular science 1,2 . Chiroptical methods typically measure small differences, or dissymmetries, in the interaction of left-and right-circularly polarised light, the chiral probe, with a chiral material 2 . However, the inherent weakness of these existing chiroptical phenomena usually restricts their application to samples of microgram level. Recently, Tang and Cohen 3 postulated that under certain circumstances superchiral electromagnetic fields could be produced that display greater chiral asymmetry than circularly polarised plane light waves. We have realised such superchiral electromagnetic fields are generated in the near fields of PCMs, and can greatly enhanced the sensitivity of a chiroptical measurement, enabling us to detect and characterise just a few picograms of a chiral material.PCMs were first fabricated, and shown to display large chiroptical effects such as optical rotation, by Schwanecke and co-workers 4 and Gonokami and co-workers 5 .The PCMs used in this study, Fig. 1 (a), are composed of left or right handed (LH / RH) Au gammadions, of length 400 nm and thickness 100 nm (plus a 5 nm Cr adhesion layer) deposited on a glass substrate and arranged in a square lattice with a periodicity of 800 nm. As a control we repeated all experiments using a metamaterial composed of achiral crosses with the same thickness and periodicity as the gammadions: these structures showed no dissymmetry in excita...

Bottom-up strategies can be effectively implemented for the fabrication of atomically precise graphene nanoribbons. Recently, using 10,10'-dibromo-9,9'-bianthracene (DBBA) as a molecular precursor to grow armchair nanoribbons on Au(111) and Cu(111), we have shown that substrate activity considerably affects the dynamics of ribbon formation, nonetheless without significant modifications in the growth mechanism. In this paper we compare the on-surface reaction pathways for DBBA molecules on Cu(111) and Cu(110). Evolution of both systems has been studied via a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and theoretical calculations. Experimental and theoretical results reveal a significant increase in reactivity for the open and anisotropic Cu(110) surface in comparison with the close-packed Cu(111). This increased reactivity results in a predominance of the molecular-substrate interaction over the intermolecular one, which has a critical impact on the transformations of DBBA on Cu(110). Unlike DBBA on Cu(111), the Ullmann coupling cannot be realized for DBBA/Cu(110) and the growth of nanoribbons via this mechanism is blocked. Instead, annealing of DBBA on Cu(110) at 250 °C results in the formation of a new structure: quasi-zero-dimensional flat nanographenes. Each nanographene unit has dehydrogenated zigzag edges bonded to the underlying Cu rows and oriented with the hydrogen-terminated armchair edge parallel to the [1-10] direction. Strong bonding of nanographene to the substrate manifests itself in a high adsorption energy of -12.7 eV and significant charge transfer of 3.46e from the copper surface. Nanographene units coordinated with bromine adatoms are able to arrange in highly regular arrays potentially suitable for nanotemplating.

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