Gold nanoparticles with complex anisotropic geometries offer unique opportunities for tailoring plasmonic near-fields beyond the limits of conventional nanorods. Here we combine photon-induced near-field electron microscopy (PINEM) and full-wave simulations to resolve plasmon hybridization and near-field localization in gold dog-bone nanoparticles and their dimers with and without conformal SiO2 shells. We demonstrate that the dog-bone geometry drives unconventional polarization-dependent field confinement, including pronounced tip-localized near-fields under both longitudinal and transverse excitation. Conformal SiO2 shells red-shift the plasmon resonances through dielectric screening and prevent charge-transfer coupling in adjacent dimers. Depending on the dimer orientation and excitation polarization, coupled structures exhibit distinct bonding- and antibonding-like hybridized modes as well as interparticle near-field channels. However, weakly interacting dimers retain largely independent particle responses with geometry-governed asymmetries. The close agreement between PINEM measurements and simulations establishes a direct picture of how shape, dielectric environment, and nanoscale coupling together define plasmonic modes in complex anisotropic nanoparticles. These findings provide design principles for engineering localized optical fields in plasmonic nanoscale structures.

Nanostructures intrinsically possessing two different structural or functional features, often called Janus nanoparticles, are emerging as a potential material for sensing, catalysis, and biomedical applications. Herein, we report the synthesis of plasmonic gold Janus nanostars (NSs) possessing a smooth concave pentagonal morphology with sharp tips and edges on one side and, contrastingly, a crumbled morphology on the other. The methodology reported herein for their synthesis - a single-step growth reaction - is different from any other Janus nanoparticle preparation involving either template-assisted growth or a masking technique. Interestingly, the coexistence of lower- and higher-index facets was found in these Janus NSs. The general paradigm for synthesizing gold Janus NSs was investigated by understanding the kinetic control mechanism with the combinatorial effect of all the reagents responsible for the structure. The optical properties of the Janus NSs were realized by corelating their extinction spectra with the simulated data. The size-dependent surface-enhanced Raman scattering (SERS) activity of these Janus NSs was studied with 1,4-BDT as the model analyte. Finite-difference time-domain simulations for differently sized particles revealed the distribution of electromagnetic hot-spots over the particles resulting in enhancement of the SERS signal in a size-dependent manner.

The practical applicability of thiolated metal-organic frameworks (MOFs) remains challenging due to their low crystallinity and transient stability. Herein, we present a one-pot solvothermal synthesis process using varying ratios of 2,5-dimercaptoterephthalic acid (DMBD) and 1,4-benzene dicarboxylic acid (100/0, 75/25, 50/50, 25/75, and 0/100) to prepare stable mixed-linker UiO-66-(SH)2 MOFs (ML-U66SX). For each variant, the effects of different linker ratios on the crystallinity, defectiveness, porosity, and particle size have been discussed in detail. In addition, the impact of modulator concentration on these features has also been described. The stability of ML-U66SX MOFs was investigated under reductive and oxidative chemical conditions. The mixed-linker MOFs were used as sacrificial catalyst supports to highlight the interplay of template stability on the rate of the gold-catalyzed 4-nitrophenol hydrogenation reaction. The release of catalytically active gold nanoclusters originating from the framework collapse decreased with the controlled DMBD proportion, resulting in a 59% drop in the normalized rate constants (9.11-3.73 s-1 mg-1). In addition, post-synthetic oxidation (PSO) was used to further probe the stability of the mixed-linker thiol MOFs under harsh oxidative conditions. Following oxidation, the UiO-66-(SH)2 MOF underwent immediate structural breakdown, unlike other mixed-linker variants. Along with crystallinity, the microporous surface area of the post-synthetically oxidized UiO-66-(SH)2 MOF could be increased from 0 to 739 m2 g-1. Thus, the present study delineates a mixed-linker strategy to stabilize the UiO-66-(SH)2 MOF under harsh chemical conditions through meticulous thiol decoration.

Synthesis, storage, and characterization of thiol functionalized metal-organic frameworks (MOFs) is highly challenging. However, they continue to be of great interest due to their broad spectrum of applications. In this work, for the first time, a solid solution approach has been adopted to dilute the thiol content in UiO-66-(SH)2 [Universitetet i Oslo] MOF by terephthalic acid linker without influencing its topology. The solid dilution had an overall impact on the crystallinity, defects, porosity and particle size of the UiO-66-(SH)2 framework. This study has the potential to significantly influence the syntheses of nanoscale thiol functionalized MOF materials and their applications in photocatalysis, water purification and drug delivery. This work also incorporates the performance study of the mixed-linker thiol MOFs under reductive and oxidative conditions. The rate of para-nitrophenolate hydrogenation under reductive conditions were mainly governed by the stability of the mixed-linker MOFs as catalyst supports. Whereas, post synthetic oxidation (PSO) was used to produce sulfonic acid tagged mixed-linker UiO-66 frameworks to probe the behavioral pattern in oxidative conditions of the parent mixed-linker thiol MOFs. The mixed-linker strategy was critical in preventing the frameworks from losing their crystallinity and porosity, upon oxidation. Thus, this work also paves the way for a general strategy to impart stability to thiol tagged UiO-66 framework having wide ranging applications.

The role of polymers has played a crucial role in developing templates that can promote regeneration as tissue-engineered matrices. The present study aims to develop functional matrices involving the protein mucin. The mucin used in this study is characterised using MALDI-TOF TOF and CD spectroscopy prior to conjugation. Thereupon, a hybrid scaffold comprising of a polysaccharide, chitosan, chemically conjugated to a protein, mucin, and encapsulated with montmorillonite is developed. Grafting of hydroxyethyl methacrylate (HEMA) is done to overcome the issue of mechanical weakness that mucin hydrogels usually undergo. It was observed that the presence of montmorillonite led to the stability of the hydrogels. The conjugations with varied ratios of the polysaccharide and protein were characterized using spectroscopic techniques. The prepared gels showed appreciable material properties in terms of water uptake and porosity. Hydrogels with different ratios of the polysaccharide and protein were evaluated for their biocompatibility. The biological evaluation of the hydrogels was performed with MC3T3E1 and C2C12 cell lines indicating their potential for wider tissue engineering applications.

Fenugreek gum is modified using two different techniques: microwave-assisted and thermal synthesis technique of graft copolymerization. The synthesis was done by varying the concentration of acrylamide monomer and CAN initiator to get the best-grafted product. The physicochemical characteristics were determined by elemental analysis, FTIR spectroscopy, SEM, XRD, DSC, TGA, number-average molecular weight and intrinsic viscosity. All the grafted materials were tested by flocculation of different synthetic suspension media as well as river water. The process of deflocculation and refloccculation was also carried out and it was observed that refloccculation process has a good potential as the flocculation efficacy increased to a considerable extent. The flocculation efficacy increased from 92.05% to 94.32% upto a maximum of 95.98% in refloccculation process. The flocculation efficacy was found out to be 95.98%, 40.52% and 68.94% respectively kaolin, coal fine and iron ore suspensions. Flocculation was done in kaolin suspension of pH 2, 4, 7 and 10 and at different temperature range of 100, 250, 400 and 550C. It is expected that this material can be used as a highly efficient flocculant in future.