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Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

Lepage D, Carrier D, Jiménez A, Beauvais J, Dubowski JJ - Nanoscale Res Lett (2011)

Bottom Line: The result is an increased traceability of the SPR shifts for biosensing applications.The surface roughness and dielectric values for various deposition rates of very thin Au films are measured.We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Computer Engineering, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada. Jan.J.Dubowski@USherbrooke.ca.

ABSTRACT
A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in the measured signal. The result is an increased traceability of the SPR shifts for biosensing applications. The main system limitation is the propagation distance of the coupled plasmon modes. This aspect is therefore studied for thin film microstructures operating in the visible and near-infrared spectral regions. The surface roughness of the substrate layer is examined for different dielectrics and deposition methods. The Au layer, on which the plasmonic modes are propagating and the biosensing occurs, is also examined. The surface roughness and dielectric values for various deposition rates of very thin Au films are measured. We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

No MeSH data available.


Related in: MedlinePlus

Far field SPR interferometric signal for an array of grating pairs;(a) Evolution of the signal under a change of the refractive index. The refractive index of a flat, 250-nm thick, layer overlying the interface is increased by Δn to emulate the increase in the average concentration of a molecular monolayer on top of the gold surface. Thicker layers would induce a steeper shift in λo. For the presented case, ΛSP = 31.8 μm. (b) Effect of the propagation lengths on the interference fringes' signal quality. The shift of the curves baseline is due to the simulated increase in the metal absorption. The dotted black curve (fully shown in inset) presents the infinite grating scenario: more power is coupled to the surface and no interference is visible, as there are no cavities.
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Figure 2: Far field SPR interferometric signal for an array of grating pairs;(a) Evolution of the signal under a change of the refractive index. The refractive index of a flat, 250-nm thick, layer overlying the interface is increased by Δn to emulate the increase in the average concentration of a molecular monolayer on top of the gold surface. Thicker layers would induce a steeper shift in λo. For the presented case, ΛSP = 31.8 μm. (b) Effect of the propagation lengths on the interference fringes' signal quality. The shift of the curves baseline is due to the simulated increase in the metal absorption. The dotted black curve (fully shown in inset) presents the infinite grating scenario: more power is coupled to the surface and no interference is visible, as there are no cavities.

Mentions: To demonstrate the ability of the SPR interferometric architecture to produce a multiplexed signal, finite element method (FEM) simulations were carried out using COMSOL Multiphysics™ v3.5a software in conjunction with Matlab®, expanding from the results reported in [4] by increasing the number of finite gratings. The resulting multiple interference increases the measured signal's quality factor. The results presented in Figure 2 were simulated for a semi-infinite flat interface of Au and air, with a regular array of finite gratings, evenly separated and illuminated as in Figure 1. The 20-nm high sinusoidal gratings have a periodicity of PG = 805 nm, are 8.57 μm in length (10⋅λSP at 1.4251 eV) and are spaced by 18.85 μm (22⋅λSP at 1.4251 eV), where λSP denotes the wavelength of the SPs. The incident light ranges from 1.28 to 1.61 eV (λo = 770 to 970 nm) and is normally incident to the surface. Figure 2a illustrates the dependence of the reflected (Ro) SPR interferometric signal on the changes in the refractive index of a 250-nm thick layer deposited atop of the investigated microstructure. In this figure, the number of traceable SPR intensity minima is multiplied by the interferences fringes. By the central limit theorem in statistical theory [5], the precision of the absolute SPR shift is increased by N1/2, where N denotes the number of interference fringes. The number of interference fringes is directly proportional to the cavity's optical length bounded by ΛSP. The fringes measurability (intensity vs. background) is also a function of ΛSP. This is shown in Figure 2b, where the impact of ΛSP on the interference signal quality is depicted. As presented, the propagation length has a severe impact on signal quality for a specific architecture, as a shorter propagation length leads to a larger difference in amplitude between two SP modes interfering. This difference reduces the interferometric signal's amplitude in relation to the background reference, resulting in a reduced S/N ratio. To make use of the SPR interferometry for biosensing, the SPs propagation distance should be as long as possible.


Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

Lepage D, Carrier D, Jiménez A, Beauvais J, Dubowski JJ - Nanoscale Res Lett (2011)

Far field SPR interferometric signal for an array of grating pairs;(a) Evolution of the signal under a change of the refractive index. The refractive index of a flat, 250-nm thick, layer overlying the interface is increased by Δn to emulate the increase in the average concentration of a molecular monolayer on top of the gold surface. Thicker layers would induce a steeper shift in λo. For the presented case, ΛSP = 31.8 μm. (b) Effect of the propagation lengths on the interference fringes' signal quality. The shift of the curves baseline is due to the simulated increase in the metal absorption. The dotted black curve (fully shown in inset) presents the infinite grating scenario: more power is coupled to the surface and no interference is visible, as there are no cavities.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211481&req=5

Figure 2: Far field SPR interferometric signal for an array of grating pairs;(a) Evolution of the signal under a change of the refractive index. The refractive index of a flat, 250-nm thick, layer overlying the interface is increased by Δn to emulate the increase in the average concentration of a molecular monolayer on top of the gold surface. Thicker layers would induce a steeper shift in λo. For the presented case, ΛSP = 31.8 μm. (b) Effect of the propagation lengths on the interference fringes' signal quality. The shift of the curves baseline is due to the simulated increase in the metal absorption. The dotted black curve (fully shown in inset) presents the infinite grating scenario: more power is coupled to the surface and no interference is visible, as there are no cavities.
Mentions: To demonstrate the ability of the SPR interferometric architecture to produce a multiplexed signal, finite element method (FEM) simulations were carried out using COMSOL Multiphysics™ v3.5a software in conjunction with Matlab®, expanding from the results reported in [4] by increasing the number of finite gratings. The resulting multiple interference increases the measured signal's quality factor. The results presented in Figure 2 were simulated for a semi-infinite flat interface of Au and air, with a regular array of finite gratings, evenly separated and illuminated as in Figure 1. The 20-nm high sinusoidal gratings have a periodicity of PG = 805 nm, are 8.57 μm in length (10⋅λSP at 1.4251 eV) and are spaced by 18.85 μm (22⋅λSP at 1.4251 eV), where λSP denotes the wavelength of the SPs. The incident light ranges from 1.28 to 1.61 eV (λo = 770 to 970 nm) and is normally incident to the surface. Figure 2a illustrates the dependence of the reflected (Ro) SPR interferometric signal on the changes in the refractive index of a 250-nm thick layer deposited atop of the investigated microstructure. In this figure, the number of traceable SPR intensity minima is multiplied by the interferences fringes. By the central limit theorem in statistical theory [5], the precision of the absolute SPR shift is increased by N1/2, where N denotes the number of interference fringes. The number of interference fringes is directly proportional to the cavity's optical length bounded by ΛSP. The fringes measurability (intensity vs. background) is also a function of ΛSP. This is shown in Figure 2b, where the impact of ΛSP on the interference signal quality is depicted. As presented, the propagation length has a severe impact on signal quality for a specific architecture, as a shorter propagation length leads to a larger difference in amplitude between two SP modes interfering. This difference reduces the interferometric signal's amplitude in relation to the background reference, resulting in a reduced S/N ratio. To make use of the SPR interferometry for biosensing, the SPs propagation distance should be as long as possible.

Bottom Line: The result is an increased traceability of the SPR shifts for biosensing applications.The surface roughness and dielectric values for various deposition rates of very thin Au films are measured.We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Computer Engineering, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada. Jan.J.Dubowski@USherbrooke.ca.

ABSTRACT
A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in the measured signal. The result is an increased traceability of the SPR shifts for biosensing applications. The main system limitation is the propagation distance of the coupled plasmon modes. This aspect is therefore studied for thin film microstructures operating in the visible and near-infrared spectral regions. The surface roughness of the substrate layer is examined for different dielectrics and deposition methods. The Au layer, on which the plasmonic modes are propagating and the biosensing occurs, is also examined. The surface roughness and dielectric values for various deposition rates of very thin Au films are measured. We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

No MeSH data available.


Related in: MedlinePlus