Surface Plasmon Resonances of Clustered Nanoparticles

Real Time SPR Assessment of the Structural Changes of Adaptive Dynamic Constitutional Frameworks as a New Route for Sensing

Cross linked gold-dynamic constitutional frameworks (DCFs) are functional materials of potential relevance for biosensing applications, given their adaptivity and high responsivity against various external stimuli (such as pH, temperature) or specific interactions with biomolecules (enzymes or DNA) via internal constitutional dynamics. However, characterization and assessment of their dynamic conformational changes in response to external stimuli has never been reported. This study proves the capability of Surface Plasmon Resonance (SPR) assays to analyse the adaptive structural modulation of a functional matrix encompassing 3D gold-dynamic constitutional frameworks (Au-DCFs) when exposed to pH variations, as external stimuli. We analyse Au-DCFs formed from Au nanoparticles, (AuNP) connected through constitutionally dynamic polymers, dynamers, with multiple functionalities. For increased generality of this proof-of-concept assay, Au-DCFs, involving DCFs designed from 1,3,5-benzene-tricarbaldehyde (BTA) connecting centres and polyethylene glycol (PEG) connectors, are covalently attached to standard SPR sensing chips (Au nanolayers, carboxyl terminated or with carboxymethyl dextran, CMD top-layer) and analysed using state-of-the art SPR instrumentation. The SPR effects of the distance from the Au-DCFs matrix to the Au nanolayer of the sensing chip, as well as of Au-DCFs thickness were investigated. This study reveals the SPR response, augmented by the AuNP, to the conformational change, i.e., shrinkage, of the dynamer and AuNP matrix when decreasing the pH, and provides an unexplored insight into the sensing applicability of SPR real-time analysis of adaptive functional materials.

Analytical results regarding electrostatic resonances of surface phonon/plasmon polaritons: separation of variables with a twist

The boundary integral equation (BIE) method ascertains explicit relations between localized surface phonon and plasmon polariton resonances and the eigenvalues of its associated electrostatic operator. We show that group-theoretical analysis of the Laplace equation can be used to calculate the full set of eigenvalues and eigenfunctions of the electrostatic operator for shapes and shells described by separable coordinate systems. These results not only unify and generalize many existing studies, but also offer us the opportunity to expand the study of phenomena such as cloaking by anomalous localized resonance. Hence, we calculate the eigenvalues and eigenfunctions of elliptic and circular cylinders. We illustrate the benefits of using the BIE method to interpret recent experiments involving localized surface phonon polariton resonances and the size scaling of plasmon resonances in graphene nanodiscs. Finally, symmetry-based operator analysis can be extended from the electrostatic to the full-wave regime. Thus, bound states of light in the continuum can be studied for shapes beyond spherical configurations.