title: Demonstration of an ultrasensitive refractive-index plasmonic sensor by enabling its quadrupole resonance in phase interrogation.
abstract: We present an ultrasensitive plasmonic sensing system by introducing a nanostructured X-shaped plasmonic sensor (XPS) and measuring its localized optical properties in phase interrogation. Our tailored XPS exhibits two major resonant modes of a low-order dipole and a high-order quadrupole, between which the quadrupole resonance allows an ultrahigh sensitivity, due to its higher quality factor. Furthermore, we design an in-house common-path phase-interrogation system, in contrast to conventional wavelength-interrogation methods, to achieve greater sensing capability. The experimental measurement shows that the sensing resolution of the XPS reaches 1.15×10(-6) RIU, not only two orders of magnitude greater than the result of the controlled extinction measurement (i.e., 9.90×10(-5) RIU), but also superior than current reported plasmonic sensors.
authors.forename: Hsin-Cheng
authors.initials: HC
authors.lastname: Lee
authors.forename: Chung-Tien
authors.initials: CT
authors.lastname: Li
authors.forename: How-Foo
authors.initials: HF
authors.lastname: Chen
authors.forename: Ta-Jen
authors.initials: TJ
authors.lastname: Yen
mesh_terms: D005898:Glass; D006046:Gold; D036103:Nanotechnology; D012031:Refractometry / Q000295:instrumentation*; D020349:Surface Plasmon Resonance / Q000295:instrumentation*
chemical_list: D006046:Gold