An Interference Localized Surface Plasmon Resonance Biosensor Based on the Photonic Structure of Au Nanoparticles and SiO2 /Si Multilayers

The localized surface plasmon reso-nance (LSPR) of noble metal nano-particles have been described in nu-merous articles.1 9Changes in the peakintensity and wavelength of plasmon spec-tra, which are caused by the refractive index(RI) variations that result from the bindingof molecules to the metal nanoparticles areoptically detectable parameters in biopho-tonics and biosensor devices.10 13How-ever, the sensitivity and accuracy of currentLSPR biosensors require further improve-ment for the field of analytical chemistry,owing to the unwanted noise that risesfrom the variants of nonspecific binding molecules.14 1In addition, finding a novelnanostructure design with special optical properties is always an attractive lure for researchers.In this work, we report a vanguard com-bination of plasmonic metal nanoparticles and photonic thin-film multilayers on an in-terference LSPR (iLSPR) substrate. The thin-film multilayers of a silicon dioxide/silicon(SiO2/Si) substrate consisting of transparentand semitransparent multilayers showed well-resolved Fabry Perot fringes under light illumination. Such structures havebeen used for biosensors,17,18since theFabry Perot fringe pattern undergoes wavelength shifts upon molecule bindings. Additionally, it was established that a two-dimensional assembly of gold nanoparti-cles, which could be regarded as a thin film,still retained the optical characteristics ofthe original nanoparticles.19,20Inspired bythe combination of these ideas, we took apioneering step to propose an innovative multilayer nanostructure with the surfacecomposed of gold nanoparticles. Experi-mental reflection spectra of our iLSPR sub-strate were numerically confirmed by simu-lations using a combination of complex Fresnel coefficients21,22and theMaxwell Garnett effective mediumtheory.23,24When the RI of the surround-ing medium increased, an obvious spectral band coupled with LSPR appeared in the in-terference pattern of the reflection spec-trum. This indicates a great potential to de-velop novel iLSPR based biosensors for thelabel-free detection of biomolecules in an arbitrary solution.

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