Long Range Surface Plasmons for Observation of Biomolecular Binding Events at Metallic Surfaces

Abstract

A long range surface plasmon (LRSP) is an electromagnetic wave propagating along a thin metal film with an order of magnitude lower damping than conventional surface plasmon (SP) waves. Thus, the excitation of LRSP is associated with a narrower resonance and it provides larger enhancement of intensity of the electromagnetic field. In surface plasmon resonance (SPR) biosensors, these features allow a more precise observation of the binding of biomolecules in the proximity to the metal surface by using the (label-free) measurement of refractive index (RI) variations and by SP-enhanced fluorescence spectroscopy. In this contribution, we investigate LRSPs excited on a layer structure consisting of a fluoropolymer buffer layer, a thin gold film, and an aqueous sample. By implementing such structure in an SPR sensor, we achieved a 2.4-and 4.4-fold improvement of the resolution in the label-free and fluorescence-based detection, respectively, of the binding of biomolecules in the close proximity to the surface. Moreover, we demonstrate that the sensor resolution can be improved by a factor of 14 and 12 for the labelfree and fluorescence-based detection, respectively, if the biomolecular binding events occur within the whole evanescent field of LRSP.

Ultra-thin gold films on transparent polymers

“…We note, however, that this is not a general rule for polymers, as very different results were obtained for gold films, e.g., on fluoropolymers in Ref. [ 17 ].…”

“…Fabrication of structurally continuous gold films below 15 -20 nm is, in general, difficult to achieve on commonly used optical surfaces, including amorphous and crystalline materials such as glass [ 13 ], native silicon oxide [ 14 ], Si 3 N 4 [ 15 ], TiO 2 [ 16 ], and certain transparent polymers [ 17 ]. For a range of crystalline substrates, including sapphire, mica, silicon, NaCl , KCl, and LiF [ 9 , 11 , 18 , 19 ], epitaxial single-crystal gold islands or sheets can be formed.…”

Surface plasmon optical sensor with enhanced sensitivity using top ZnO thin film

“…The guided wave SPR (GWSPR) configuration is similar to the SPR with an addition of a thin film between the metal layer and dielectric cover thick enough to support guided modes. The resolution of a SPR sensor is improved as the linewidth of the SPR reflectivity dip curve decreases and a shift in the resonance angle or wavelength in response to the environmental index change increases [17,18]. With limited available metals for plasmonic application, most current efforts have been concentrated on decreasing the linewidth of the resonance curve [19][20][21].…”

Surface plasmon-enhanced fluorescence on Au nanohole array for prostate-specific antigen detection

“…The field enhancement by PSP could be further improved up to 60-fold by the excitation of long-range SP on a gold thin film coated on a dielectric layer having its refractive index close to water. [34][35][36][37] Compared with the PSP on a metallic thin film, the LSP on metallic nanostructures typically offers higher confinement of the field with a penetration depth L p from several to tens of nanometers, which is about tenfold lower than the conventional PSP (L p =180 nm). Such a highly confined LSP field on nanostructures has demonstrated a fluorescence enhancement of about 10-to 200-fold on an averaged area and 1,300-fold for a single dye positioned on the hot spot of a bowtie nanoantenna.…”