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Narrow groove plasmonic nano-gratings for surface plasmon resonance sensing.

Dhawan A, Canva M, Vo-Dinh T - Opt Express (2011)

Bottom Line: We present a novel surface plasmon resonance (SPR) configuration based on narrow groove (sub-15 nm) plasmonic nano-gratings such that normally incident radiation can be coupled into surface plasmons without the use of prism-coupling based total internal reflection, as in the classical Kretschmann configuration.Our calculations indicate substantially higher differential reflectance signals, on localized change of refractive index in the narrow groove plasmonic gratings, as compared to those obtained from conventional SPR-based sensing systems.Furthermore, these calculations allow determination of the optimal nano-grating geometric parameters - i. e. nanoline periodicity, spacing between the nanolines, as well as the height of the nanolines in the nano-grating - for highest sensitivity to localized change of refractive index, as would occur due to binding of a biomolecule target to a functionalized nano-grating surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.

ABSTRACT
We present a novel surface plasmon resonance (SPR) configuration based on narrow groove (sub-15 nm) plasmonic nano-gratings such that normally incident radiation can be coupled into surface plasmons without the use of prism-coupling based total internal reflection, as in the classical Kretschmann configuration. This eliminates the angular dependence requirements of SPR-based sensing and allows development of robust miniaturized SPR sensors. Simulations based on Rigorous Coupled Wave Analysis (RCWA) were carried out to numerically calculate the reflectance - from different gold and silver nano-grating structures - as a function of the localized refractive index of the media around the SPR nano-gratings as well as the incident radiation wavelength and angle of incidence. Our calculations indicate substantially higher differential reflectance signals, on localized change of refractive index in the narrow groove plasmonic gratings, as compared to those obtained from conventional SPR-based sensing systems. Furthermore, these calculations allow determination of the optimal nano-grating geometric parameters - i. e. nanoline periodicity, spacing between the nanolines, as well as the height of the nanolines in the nano-grating - for highest sensitivity to localized change of refractive index, as would occur due to binding of a biomolecule target to a functionalized nano-grating surface.

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(a) Schematic showing Kretschmann configuration conventionally employed for coupling of the incident radiation to surface plasmons and (b) Schematic showing narrow groove plasmonic (gold or silver) nano-grating structure illustrating the important dimensions and parameters. The incident and reflected radiation are indicated by symbols ‘I’ and ‘R’, respectively. While ‘M’ indicates a plasmonic film such as a gold or silver film, ‘L’ indicates a thin layer of molecules on the surface of the metallic film. ‘(P)’ and ‘(H)’ shown in the above figure indicate the periodicity and height of the nanolines in the nano-gratings and ‘(W)’ indicates the spacing between adjacent nanolines in the nano-grating.
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g001: (a) Schematic showing Kretschmann configuration conventionally employed for coupling of the incident radiation to surface plasmons and (b) Schematic showing narrow groove plasmonic (gold or silver) nano-grating structure illustrating the important dimensions and parameters. The incident and reflected radiation are indicated by symbols ‘I’ and ‘R’, respectively. While ‘M’ indicates a plasmonic film such as a gold or silver film, ‘L’ indicates a thin layer of molecules on the surface of the metallic film. ‘(P)’ and ‘(H)’ shown in the above figure indicate the periodicity and height of the nanolines in the nano-gratings and ‘(W)’ indicates the spacing between adjacent nanolines in the nano-grating.

Mentions: Plasmon resonances in metallic nanostructures - thin films, nanopillars fabricated on planar surfaces, and nanoparticles - are collective oscillations of the conduction band electrons, which are excited when radiation of certain wavelengths is incident on these nanostructures. Excitation of surface plasmons leads to an increase in the electromagnetic fields in the vicinity of metallic thin films and nanostructures and this has been exploited for the fabrication of surface plasmon resonance (SPR) based [1–7], localized surface plasmon resonance (LSPR) based [8–12] and surface-enhanced Raman scattering (SERS) based [13–17] sensors. Plasmon resonances of noble metal nanostructures (mainly gold and silver) are conventionally employed for developing SPR, LSPR, and SERS based sensors as these nanostructures resonantly scatter or absorb light in the visible and near-infrared spectra. SPR sensors are conventionally based on detecting changes of refractive indices - both in the bulk media around the metallic films or in the vicinity of the continuous metallic films having nano-scale thickness, conventionally between 30 and 60 nm - employing both angular and wavelength interrogation methods. SPR imaging (SPRI) sensors [18–20] have also been employed for chemical and biological sensing applications. SPRI sensors are based on detection of differential reflectance - before and after the localized changes of refractive indices on the surface of the plasmonic films - for the entire imaging region, given constant radiation wavelength and angle of incidence such that these satisfy the conditions for surface plasmon resonance excitation in the metallic films. Mostly, SPR sensors employ either prism coupling as shown in Fig. 1aFig. 1


Narrow groove plasmonic nano-gratings for surface plasmon resonance sensing.

Dhawan A, Canva M, Vo-Dinh T - Opt Express (2011)

(a) Schematic showing Kretschmann configuration conventionally employed for coupling of the incident radiation to surface plasmons and (b) Schematic showing narrow groove plasmonic (gold or silver) nano-grating structure illustrating the important dimensions and parameters. The incident and reflected radiation are indicated by symbols ‘I’ and ‘R’, respectively. While ‘M’ indicates a plasmonic film such as a gold or silver film, ‘L’ indicates a thin layer of molecules on the surface of the metallic film. ‘(P)’ and ‘(H)’ shown in the above figure indicate the periodicity and height of the nanolines in the nano-gratings and ‘(W)’ indicates the spacing between adjacent nanolines in the nano-grating.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368305&req=5

g001: (a) Schematic showing Kretschmann configuration conventionally employed for coupling of the incident radiation to surface plasmons and (b) Schematic showing narrow groove plasmonic (gold or silver) nano-grating structure illustrating the important dimensions and parameters. The incident and reflected radiation are indicated by symbols ‘I’ and ‘R’, respectively. While ‘M’ indicates a plasmonic film such as a gold or silver film, ‘L’ indicates a thin layer of molecules on the surface of the metallic film. ‘(P)’ and ‘(H)’ shown in the above figure indicate the periodicity and height of the nanolines in the nano-gratings and ‘(W)’ indicates the spacing between adjacent nanolines in the nano-grating.
Mentions: Plasmon resonances in metallic nanostructures - thin films, nanopillars fabricated on planar surfaces, and nanoparticles - are collective oscillations of the conduction band electrons, which are excited when radiation of certain wavelengths is incident on these nanostructures. Excitation of surface plasmons leads to an increase in the electromagnetic fields in the vicinity of metallic thin films and nanostructures and this has been exploited for the fabrication of surface plasmon resonance (SPR) based [1–7], localized surface plasmon resonance (LSPR) based [8–12] and surface-enhanced Raman scattering (SERS) based [13–17] sensors. Plasmon resonances of noble metal nanostructures (mainly gold and silver) are conventionally employed for developing SPR, LSPR, and SERS based sensors as these nanostructures resonantly scatter or absorb light in the visible and near-infrared spectra. SPR sensors are conventionally based on detecting changes of refractive indices - both in the bulk media around the metallic films or in the vicinity of the continuous metallic films having nano-scale thickness, conventionally between 30 and 60 nm - employing both angular and wavelength interrogation methods. SPR imaging (SPRI) sensors [18–20] have also been employed for chemical and biological sensing applications. SPRI sensors are based on detection of differential reflectance - before and after the localized changes of refractive indices on the surface of the plasmonic films - for the entire imaging region, given constant radiation wavelength and angle of incidence such that these satisfy the conditions for surface plasmon resonance excitation in the metallic films. Mostly, SPR sensors employ either prism coupling as shown in Fig. 1aFig. 1

Bottom Line: We present a novel surface plasmon resonance (SPR) configuration based on narrow groove (sub-15 nm) plasmonic nano-gratings such that normally incident radiation can be coupled into surface plasmons without the use of prism-coupling based total internal reflection, as in the classical Kretschmann configuration.Our calculations indicate substantially higher differential reflectance signals, on localized change of refractive index in the narrow groove plasmonic gratings, as compared to those obtained from conventional SPR-based sensing systems.Furthermore, these calculations allow determination of the optimal nano-grating geometric parameters - i. e. nanoline periodicity, spacing between the nanolines, as well as the height of the nanolines in the nano-grating - for highest sensitivity to localized change of refractive index, as would occur due to binding of a biomolecule target to a functionalized nano-grating surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.

ABSTRACT
We present a novel surface plasmon resonance (SPR) configuration based on narrow groove (sub-15 nm) plasmonic nano-gratings such that normally incident radiation can be coupled into surface plasmons without the use of prism-coupling based total internal reflection, as in the classical Kretschmann configuration. This eliminates the angular dependence requirements of SPR-based sensing and allows development of robust miniaturized SPR sensors. Simulations based on Rigorous Coupled Wave Analysis (RCWA) were carried out to numerically calculate the reflectance - from different gold and silver nano-grating structures - as a function of the localized refractive index of the media around the SPR nano-gratings as well as the incident radiation wavelength and angle of incidence. Our calculations indicate substantially higher differential reflectance signals, on localized change of refractive index in the narrow groove plasmonic gratings, as compared to those obtained from conventional SPR-based sensing systems. Furthermore, these calculations allow determination of the optimal nano-grating geometric parameters - i. e. nanoline periodicity, spacing between the nanolines, as well as the height of the nanolines in the nano-grating - for highest sensitivity to localized change of refractive index, as would occur due to binding of a biomolecule target to a functionalized nano-grating surface.

Show MeSH
Related in: MedlinePlus