Abstract
The resonant wave modes in monomodal and multimodal planar Surface Plasmon Resonance (SPR) sensors and their response to a bidimensional array of gold nanoparticles (AuNPs) are analyzed both theoretically and experimentally, to investigate the parameters that rule the correct nanoparticle counting in the emerging metal nanoparticle-amplified surface plasmon resonance (PA-SPR) spectroscopy. With numerical simulations based on the Finite Element Method (FEM), we evaluate the error performed in the determination of the surface density of nanoparticles σ when the Maxwell-Garnett effective medium theory is used for fast data processing of the SPR reflectivity curves upon nanoparticle detection. The deviation increases directly with the manifestations of non-negligible scattering cross-section of the single nanoparticle, dipole-dipole interactions between adjacent AuNPs and dipolar interactions with the metal substrate. Near field simulations show clearly the set-up of dipolar interactions when the dielectric thickness is smaller than 10 nm and confirm that the anomalous dispersion usually observed experimentally is due to the failure of the effective medium theories. Using citrate stabilized AuNPs with a nominal diameter of about 15 nm, we demonstrate experimentally that Dielectric Loaded Waveguides (DLWGs) can be used as accurate nanocounters in the range of surface density between 20 and 200 NP/µm2, opening the way to the use of PA-SPR spectroscopy on systems mimicking the physiological cell membranes on SiO2 supports.
Highlights
IntroductionThe detection principle of Surface Plasmon Resonance (SPR) sensors is based on the perturbation of the near electromagnetic field at the metal-dielectric interface of the sensing platform, provoked by the interaction of the external surface with the analytes of interest [2]
Surface plasmon resonance (SPR) spectroscopy, is today one of the principal optical techniques used for the development of low cost and high resolution chemical and bio-chemical optical sensors [1].The detection principle of Surface Plasmon Resonance (SPR) sensors is based on the perturbation of the near electromagnetic field at the metal-dielectric interface of the sensing platform, provoked by the interaction of the external surface with the analytes of interest [2]
We analyzed in details the limits of the Maxwell-Garnett theory in the determination of the surface density σ of attached to the surface of gold nanoparticles (AuNPs) in particle amplified surface plasmon resonance (PA-SPR) spectroscopy
Summary
The detection principle of SPR sensors is based on the perturbation of the near electromagnetic field at the metal-dielectric interface of the sensing platform, provoked by the interaction of the external surface with the analytes of interest [2]. The spatial overlap between the analytes and the evanescent electromagnetic field of the surface plasmon polariton (SPP) propagating along the metal-dielectric interface, has to be taken in account for the determination of the geometrical properties of the sensing platforms necessary to obtain the higher sensitivity. The monitoring of the interaction of bio-molecules with systems mimicking the physiological cell membranes on solid supports is performed with the best sensitivity by the use of dielectric loaded waveguide (DLWG) [8,9], due to the wider extension of the evanescent electromagnetic field of the guided modes into the external medium
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