title: Seeing protein monolayers with naked eye through plasmonic Fano resonances.
abstract: We introduce an ultrasensitive label-free detection technique based on asymmetric Fano resonances in plasmonic nanoholes with far reaching implications for point-of-care diagnostics. By exploiting extraordinary light transmission phenomena through high-quality factor (Q(solution) ∼ 200) subradiant dark modes, we experimentally demonstrate record high figures of merits (FOMs as high as 162) for intrinsic detection limits surpassing that of the gold standard prism coupled surface-plasmon sensors (Kretschmann configuration). Our experimental record high sensitivities are attributed to the nearly complete suppression of the radiative losses that are made possible by the high structural quality of the fabricated devices as well as the subradiant nature of the resonances. Steep dispersion of the plasmonic Fano resonance profiles in high-quality plasmonic sensors exhibit dramatic light intensity changes to the slightest perturbations within their local environment. As a spectacular demonstration of the extraordinary sensitivity and the quality of the fabricated biosensors, we show direct detection of a single monolayer of biomolecules with naked eye using these Fano resonances and the associated Wood's anomalies. To fabricate high optical-quality sensors, we introduce a high-throughput lift-off free evaporation fabrication technique with extremely uniform and precisely controlled nanofeatures over large areas, leading to resonance line-widths comparable to that of the ideally uniform structures as confirmed by our time-domain simulations. The demonstrated label-free sensing platform offers unique opportunities for point-of-care diagnostics in resource poor settings by eliminating the need for fluorescent labeling and optical detection instrumentation (camera, spectrometer, etc.) as well as mechanical and light isolation.
authors.affiliation: Department of Electrical and Computer Engineering, and Photonics Center, Boston University, Boston, MA 02215, USA. yanik@bu.edu
authors.forename: Ahmet A
authors.initials: AA
authors.lastname: Yanik
authors.forename: Arif E
authors.initials: AE
authors.lastname: Cetin
authors.forename: Min
authors.initials: M
authors.lastname: Huang
authors.forename: Alp
authors.initials: A
authors.lastname: Artar
authors.forename: S Hossein
authors.initials: SH
authors.lastname: Mousavi
authors.forename: Alexander
authors.initials: A
authors.lastname: Khanikaev
authors.forename: John H
authors.initials: JH
authors.lastname: Connor
authors.forename: Gennady
authors.initials: G
authors.lastname: Shvets
authors.forename: Hatice
authors.initials: H
authors.lastname: Altug
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry / Q000648:ultrastructure*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry / Q000648:ultrastructure*; D013057:Spectrum Analysis; D020349:Surface Plasmon Resonance / Q000379:methods*
chemical_list: D011506:Proteins