LSPR Coupling and Distribution of Interparticle Distances between Nanoparticles in Hydrogel on Optical Fiber End Face

Abstract

We report on a new localized surface plasmon resonance (LSPR)-based optical fiber (OF) architecture with a potential in sensor applications. The LSPR-OF system is fabricated by immobilizing gold nanoparticles (GNPs) in a hydrogel droplet polymerized on the fiber end face. This design has several advantages over earlier designs. It dramatically increase the number nanoparticles (NP) available for sensing, it offers precise control over the NP density, and the NPs are positioned in a true 3D aqueous environment. The OF-hydrogel design is also compatible with low-cost manufacturing. The LSPR-OF platform can measure volumetric changes in a stimuli-responsive hydrogel or measure binding to receptors on the NP surface. It can also be used as a two-parameter sensor by utilizing both effects. We present results from proof-of-concept experiments exploring the properties of LSPR and interparticle distances of the GNP-hydrogel OF design by characterizing the distribution of distances between NPs in the hydrogel, the refractive index of the hydrogel and the LSPR attributes of peak position, amplitude and linewidth for hydrogel deswelling controlled with pH solutions.

Mapping Nanoparticles in Hydrogels: A Comparison of Preparation Methods for Electron Microscopy

“…The LSPR response of spherical or spheroidal gold nanoparticles (GNP) in hydrogels has shown to deviate from the LSPR response of randomly distributed spherical or spheroidal GNPs [51][52][53]. The plasmon coupling between spherical GNPs occurred for an interparticle distance that was larger than the estimated plasmon coupling distance [51]. This was found to be due to the inhomogeneous distribution of the particles in the hydrogel.…”

“…The dipole-dipole coupling and RI sensitivity of the LSPR in NMNPs may as well be utilized for detecting the change in volume of stimuli-responsive hydrogels for significant swelling and deswelling. The LSPR response of spherical or spheroidal gold nanoparticles (GNP) in hydrogels has shown to deviate from the LSPR response of randomly distributed spherical or spheroidal GNPs [51][52][53]. The plasmon coupling between spherical GNPs occurred for an interparticle distance that was larger than the estimated plasmon coupling distance [51].…”

“…We have in earlier work developed proof-of-concepts of fiber optic (FO) sensors based on using NMNPs immobilized in polyacrylamide hydrogels and combining LSPR and interferometric sensing modalities [25,[50][51][52][53]. The interferometric sensing modality detects the change in volume of a stimuli-responsive hydrogel, whereas the LSPR sensing modality detects receptor-analyte recombinations on the NMNP surface.…”

“…Here, the morphology of 10 wt % polyacrylamide (AAM-BIS) and poly(acrylamide-co-acrylic acid) (AAM-AAC-BIS) hydrogels, with and without gold nanorods (GNRs) as composite materials, was studied using conventional SEM. Low GNR densities were used (10/µm 3 ) as for the earlier FO sensor studies in [51][52][53]. The hydrogels were prepared for SEM using CPD or the drying with HMDS and characterized concerning pore structures and GNR positions in the polymer network.…”

Photothermal Effect in Plasmonic Nanotip for LSPR Sensing

“…In an attempt to attain a small localized resolution, attempts have been made to equip optical fibers with nano-antennas. These studies can be categorized into three groups: (i) Those that use a geometry modified optical fiber [30][31][32], (ii) those that equip facets of a fiber with nano antenna [32][33][34][35][36], and most recently (iii) those that use a tapered fiber [37,38]. These studies [37,38] use tapered fiber tips as TERS tips.…”