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.

There has been a surge of consumer products that incorporate nanoparticles, which are used to improve or impart new functionalities to the products based on their unique physicochemical properties. With such an increase in products containing nanomaterials, there is a need to understand their potential impacts on the environment. This is often done using various biological models that are abundant in the different environmental compartments where the nanomaterials may end up after use. Beyond studying whether nanomaterials simply kill an organism, the molecular mechanisms by which nanoparticles exhibit toxicity have been extensively studied. Some of the main mechanisms include (1) direct nanoparticle association with an organism's cell surface, where the membrane can be damaged or initiate internal signaling pathways that damage the cell, (2) dissolution of the material, releasing toxic ions that impact the organism, generally through impairing important enzyme functions or through direct interaction with a cell's DNA, and (3) the generation of reactive oxygen species and subsequent oxidative stress on an organism, which can also damage important enzymes or an organism's genetic material. This Account reviews these toxicity mechanisms, presenting examples for each with different types of nanomaterials. Understanding the mechanism of nanoparticle toxicity will inform efforts to redesign nanoparticles with reduced environmental impact. The redesign strategies will need to be chosen based on the major mode of toxicity, but also considering what changes can be made to the nanomaterial without impacting its ability to perform in its intended application. To reduce interactions with the cell surface, nanomaterials can be designed to have a negative surface charge, use ligands such as polyethylene glycol that reduce protein binding, or have a morphology that discourages binding with a cell surface. To reduce the nanoparticle dissolution to toxic ions, the toxic species can be replaced with less toxic elements that have similar properties, the nanoparticle can be capped with a shell material, the morphology of the nanoparticle can be chosen to minimize surface area and thus minimize dissolution, or a chelating agent can be co-introduced or functionalized onto the nanomaterial's surface. To reduce the production of reactive oxygen species, the band gap of the material can be tuned either by using different elements or by doping, a shell layer can be added to inhibit direct contact with the core, or antioxidant molecules can be tethered to the nanoparticle surface. When redesigning nanoparticles, it will be important to test that the redesign strategy actually reduces toxicity to organisms from relevant environmental compartments. It is also necessary to confirm that the nanomaterial still demonstrates the critical physicochemical properties that inspired its inclusion in a product or device.

This work investigates the biological impact of LixNiyMnzCo1−y−zO2, a class of cathode materials used in lithium ion batteries.

This work assesses the potential of mesoporous silica nanoparticles with or without a chitosan coating to suppress Fusarium wilt (Fusarium oxysporum f. sp. niveum) in watermelon (Citrullus lanatus) by virtue of dissolution to release silicic acid. Plant health was assessed by monitoring the total biomass and fruit production in both healthy and pathogen-infected plants up to 100 days after a single nanoparticle application (500 mg/L) was applied at the seedling stage. Both types of mesoporous silica nanoparticles enhanced the innate defense mechanisms of watermelon, with mesoporous silica nanoparticles (MSNs) and chitosan-coated mesoporous silica nanoparticles (CTS-MSNs) reducing disease severity by ∼40% and ∼27%, respectively, as measured by the area-under-the-disease-progress curve. Changes in gene expression measured several weeks after nanoparticle application demonstrated reduced expression of several stress-related genes after CTS-MSN and MSN treatments, indicating a reduced disease burden on the plant. Although treatment did not impact fruit production from diseased plants, a single application of chitosan-coated mesoporous silica nanoparticles at the seedling stage led to a 70% increase in the fruit yield of uninfected watermelon. Monitoring plant biomass revealed that MSNs and CTS-MSNs had no significant impact on the biomass reductions in diseased plants, likely because seedlings were treated and biomass was measured weeks later in the fully grown plants. These findings demonstrate the utility of a single application of mesoporous silica nanoparticles with or without a chitosan coating as a nanoenabled agricultural amendment, and current work is focused on optimizing the material synthesis and treatment regimens for maximum benefit.

The authors would like to thank the two anonymous reviewers for their insightful and constructive comments that improved the quality of our work as well as the Ministry of Economic Affairs and Climate Policy of the Netherlands for its financial support enabling the research behind this publication.