title: Biomacromolecular Stereostructure Mediates Mode Hybridization in Chiral Plasmonic Nanostructures.
abstract: 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, β-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.
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Calum
authors.initials: C
authors.lastname: Jack
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.|School of Engineering, Rankine Building, University of Glasgow , Glasgow G12 8LT, United Kingdom.
authors.forename: Affar S
authors.initials: AS
authors.lastname: Karimullah
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Ross
authors.initials: R
authors.lastname: Leyman
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Ryan
authors.initials: R
authors.lastname: Tullius
authors.affiliation: Department of Chemistry, 710 N. Pleasant Street, University of Massachusetts , Amherst, Massachusetts 01003, United States.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Rotello
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Graeme
authors.initials: G
authors.lastname: Cooke
authors.affiliation: School of Engineering, Rankine Building, University of Glasgow , Glasgow G12 8LT, United Kingdom.
authors.forename: Nikolaj
authors.initials: N
authors.lastname: Gadegaard
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Laurence D
authors.initials: LD
authors.lastname: Barron
authors.affiliation: School of Chemistry, Joseph Black Building, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Kadodwala
mesh_terms: D003208:Concanavalin A; D004560:Electricity; D049329:Nanostructures; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D012031:Refractometry; D012710:Serum Albumin, Bovine
chemical_list: D011506:Proteins; D003208:Concanavalin A; D012710:Serum Albumin, Bovine
keywords: Plasmonic hybridization; biosensing; chiral plasmonics; optically active second harmonic generation