Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well. CONTENTS 1. Introduction 664 2. Synthesis of Ag and AuNPs and Stabilization with Adsorbed/Covalently Attached Ligands in Solution Phase 666 2.1. Theoretical Background of Colloidal Stability of the Plasmonic Nanoparticles 667 2.2.

Research at the interface of synthetic materials, biochemistry, and analytical techniques has enabled sensing platforms for applications across many research communities. Herein we review the materials used as affinity agents to create surface-enhanced Raman spectroscopy (SERS) sensors. Our scope includes those affinity agents (antibody, aptamer, small molecule, and polymer) that facilitate the intrinsic detection of targets relevant to biology, medicine, national security, environmental protection, and food safety. We begin with an overview of the analytical technique (SERS) and considerations for its application as a sensor. We subsequently describe four classes of affinity agents, giving a brief overview on affinity, production, attachment chemistry, and first uses with SERS. Additionally, we review the SERS features of the affinity agents, and the analytes detected by intrinsic SERS with that affinity agent class. We conclude with remarks on affinity agent selection for intrinsic SERS sensing platforms.

In this study, the engineered silica nanoparticles were prepared to possess the different dissolution behaviors, to investigate their effects on the sustainable crop protection against fungal disease.

Surface-enhanced Raman scattering (SERS)based detection of suspension-phase analytes holds great promise for a variety of applications; however, plasmonic colloidal SERS substrates are not stable in many solution conditions unless they are protected by a stabilizing agent. Mesoporous silica shells on plasmonic nanoparticle cores have been demonstrated to perform well in a variety of liquid matrices. However, this silica shell can be seen as barrier from the perspective of the analyte, as the analyte molecules need to reach the plasmonic core after they pass through the shell. In this work, mesoporous silica-coated gold nanorods have been synthesized and characterized as aqueous colloidal SERS substrates systematically considering how SERS performance is impacted by three different factors: adsorbed molecules, the silica shell, and bulk solvent media. The results show that SERS signal intensities from the model hydrophobic analyte, trans-1,2-bis(4-pyridyl) ethylene (BPE), are enhanced when the pore size, hydrophobicity of the shell, and ionic strength are increased, indicating more favorable interaction between the substrates and the analyte. The silica shell presented herein facilitates efficient adsorption of the analyte to the gold core and enhanced sensitivity to environmental refractive index changes. This efficient adsorption can be further enhanced by controlling the incubation temperature. Overall, this work reveals how substrate exposure conditions can be tuned to maximize analyte SERS signals without compromising the silica shell that protects the plasmonic properties of the SERS-enhancing core.

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The successful development of tablet formulations of many active pharmaceutical ingredients (APIs) is challenged by their poor manufacturability (e.g., flowability, tabletability) and dissolution characteristics. Here, we report a novel quasi-emulsion solvent diffusion cocrystallization (QESD-CC) method as an integrated crystal and particle engineering approach for successful generation of spherical cocrystal agglomerates of the poorly soluble drug indomethacin (IMC) and the sweet cocrystallization agent saccharin (SAC). The QESD-CC process consists of two distinct steps: (1) formation of a transient emulsion containing solvated IMC and SAC and (2) subsequent precipitation of IMC–SAC cocrystals from the emulsion as hollow spherical particles. Solution 1H NMR analyses and computational modeling studies indicated that hydroxypropyl methylcellulose (HPMC) preferentially interacts with the SAC molecules through hydrogen bonds, thus driving the polymer to form a shell that stabilizes the transient emulsion droplets and coats the resulting particles. Spherical QESD-CC particles exhibited excellent flowability, while the HPMC coating and microsize primary crystals led to excellent tabletability. Outstanding manufacturability and high cocrystal solubility thus enabled the successful development of a high-drug-loading tablet formulation comprising 46.3 wt % IMC.

This Feature describes several methods for the characterization of magnetic nanoparticles in biological matrices such as cells and tissues. The Feature focuses on sample preparation and includes several case studies where multiple techniques were used in conjunction.

Plasmonic materials show great potential for selective photocatalysis under relatively mild reaction conditions. However, the catalytic activity of these plasmonic catalysts can also depend upon the support material that stabilizes the catalysts, where the composition of the catalytic support may change the overall photocatalytic efficiency and yield. It is unknown how changes in the support material may change the plasmon-driven photocatalysis, which may be initiated by plasmon-derived hot carriers, localized heating, or enhanced electromagnetic fields. Herein, we probe the effects of catalytic supports on heating in plasmon-driven catalysis by examining various gold nanoparticle oxide systems. We use ultrafast surface-enhanced Raman thermometry to measure the effective temperature, equivalent to the vibrational kinetic energy, of reporter molecules located between plasmonic gold nanostructures and local environments ranging from ligands to mesoporous silica shells to silica shells. Upon photoexcitation, the transient effective temperature, equivalent to the energy deposited into a vibrational mode, of adsorbed molecules on the silica-coated samples increases, and the energy quickly dissipates within 3 ps. However, the baseline effective temperature that arises from the surface-enhanced Raman spectroscopy probing process depends upon the encapsulant, where the energy deposition differs by 200–300 K between the ligand-coated (citrate or CTAB) and the silica-coated samples. Adsorbates surrounded by a silica shell experience significantly higher effective temperatures than the adsorbates surrounded by ligands or solvent, likely because of the differing effective heat capacities of these media. Taken together, this work shows that a silica support impacts the localized heating of molecular adsorbates on the gold surface and may play a role in enhanced plasmonic photocatalysis because of increased thermal contributions.