Journal
ACS NANO
Volume 4, Issue 1, Pages 349-357Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn901024e
Keywords
surface plasmon resonance; localized surface plasmon resonance; sensing; biosensing; sensitivity; figure of merit; nanorods
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Funding
- Generalitat de Catalunya
- Social European Fund
- M. Botin Foundation
- Nanomag CIBER-BBN
- Ministerio de Clencia e Innovacion [MAT2007-62696, PCI2005-A7-0075]
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We present a theoretical and experimental study involving the sensing characteristics of wavelength-interrogated plasmonic sensors based on surface plasmon polaritons (SPP) in planar gold films and on localized surface plasmon resonances (LSPR) of single gold nanorods. The tunability of both sensing platforms allowed us to analyze their bulk and surface sensing characteristics as a function of the plasmon resonance position. We demonstrate that a general figure of merit (FOM), which is equivalent in wavelength and energy scales, can be employed to mutually compare both sensing schemes. Most interestingly, this FOM has revealed a spectral region for which the surface sensitivity performance of both sensor types is optimized, which we attribute to the intrinsic dielectric properties of plasmonic materials. Additionally, in good agreement with theoretical predictions, we experimentally demonstrate that, although the SPP sensor offers a much better bulk sensitivity, the LSPR sensor shows an approximately 15% better performance for surface sensitivity measurements when its FOM is optimized. However, optimization of the substrate refractive index and the accessibility of the relevant molecules to the nanoparticles can lead to a total 3-fold improvement of the FOM in LSPR sensors.
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