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Study and development of localised surface plasmon resonance based sensors using anisotropic spectroscopy

Abstract : Localised surface plasmon resonance (LSPR) is defined as the collective oscillation of the conduction electron cloud induced by an external electric field. In the case of nanoparticles composed of noble metals such as gold, silver, or copper, the resonance is located in the visible or near UV range. The polarisability of a nanoparticle is directly proportional to four key parameters: its volume, its composition, its shape and its surrounding environment. It is these properties that make LSPR useful for sensor applications. In the case of isotropic particles, such as spheres, the LSPR spectrum shows only one absorption peak. In the case of an anisotropic particle, such as an ellipsoid, the absorption spectrum has two or more distinct peaks. If the absorption cross-section is measured with unpolarised light, multiple maxima are obtained. The key point for these type of systems is the possibility to decouple the resonances using polarised light. In this description the anisotropic system is considered microscopic, i.e. it is only made of one or two particles. In the case of a macroscopic sample, such as a colloidal solution of ellipsoids or nanorods, the absorption spectrum will always have multiple absorption maxima, and they cannot be decoupled because the sample is not globally anisotropic.On the other hand, if the sample has a global anisotropy such as aligned nanorods, or nanosphere organised in lines, it is possible to have a plasmon spectrum dependent on the light polarisation. Being able to decouple the resonances of an anisotropic sample makes it possible to measure a differential spectrum by taking the difference of the two absorption spectra. This is experimentally possible by using anisotropic transmission spectroscopy which measures the optical anisotropy. The advantage is to obtain a relative and differential spectrum more stable and reproducible. Moreover, it is now possible to follow the evolution of the optical response of the plasmonic particles no longer by measuring a spectral shift but by measuring the change in intensity of the signal at a fixed wavelength. This method is used on two case studies which are the measurement of the interaction of dihydrogen with gold nanoparticles, as well as the detection of low partial pressure of dihydrogen in a carrier gas (argon, and air) using palladium nanoparticles, for hydrogen sensing applications.
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William L. Watkins. Study and development of localised surface plasmon resonance based sensors using anisotropic spectroscopy. Chemical Physics [physics.chem-ph]. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS505⟩. ⟨tel-02285647v2⟩

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