Dilution destabilizes engineered ligand-coated nanoparticles in aqueous suspensions.

It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one because dilution reduces collision rates of the particles and therefore delays the formation of aggregates. However, this generalization does not apply for some engineered ligand-coated nanoparticles (NPs). We observed the opposite relationship between stability and concentration of NPs. We tested 4 different types of NPs: CdSe-11-mercaptoundecanoic acid, CdTe-polyelectrolytes, Ag-citrate, and Ag-polyvinylpyrrolidone. The results showed that dilution alone induced aggregation and subsequent sedimentation of the NPs that were originally monodispersed at very high concentrations. Increased dilution caused NPs to progressively become unstable in the suspensions. The extent of the dilution impact on the stability of NPs is different for different types of NPs. We hypothesize that the unavoidable decrease in free ligand concentration in the aqueous phase following dilution causes detachment of ligands from the suspended NP cores. The ligands attached to NP core surfaces must generally approach exchange equilibrium with free ligands in the aqueous phase; therefore, ligand detachment and destabilization are expected consequences of dilution. More studies are necessary to test this hypothesis. Because the stability of NPs determines their physicochemical and kinetic behavior including toxicity, dilution-induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated NPs in aqueous systems. Environ Toxicol Chem 2018;37:1301-1308. © 2018 SETAC.

Advancing safer alternatives through functional substitution.

To achieve the ultimate goal of sustainable chemicals management policy­the transition to safer chemicals, materials, products, and processes­current chemicals management approaches could benefit from a broader perspective. Starting with considerations of function, rather than characterizing and managing risks associated with a particular chemical, may provide a different, solutions-oriented lens to reduce risk associated with the uses of chemicals. It may also offer an efficient means, complementing existing tools, to reorient chemicals management approaches from time-intensive risk assessment and risk management based on single chemicals to comparative evaluation of the best options to fulfill a specific function. This article describes a functional approach to chemicals management we call "functional substitution" that encourages decision-makers to look beyond chemical by chemical substitution to find a range of alternatives to meet product performance. We define functional substitution, outline a rationale for greater use of this concept when considering risks posed by uses of chemicals, and provide examples of how functional approaches have been applied toward the identification of alternatives. We also discuss next steps for implementing functional substitution in chemical assessment and policy development.

Collaboration across disciplines for sustainability: green chemistry as an emerging multistakeholder community.

Sustainable solutions to our nation's material and energy needs must consider environmental, health, and social impacts while developing new technologies. Building a framework to support interdisciplinary interactions and incorporate sustainability goals into the research and development process will benefit green chemistry and other sciences. This paper explores the contributions that diverse disciplines can provide to the design of greener technologies. These interactions have the potential to create technologies that simultaneously minimize environmental and health impacts by drawing on the combined expertise of students and faculty in chemical sciences, engineering, environmental health, social sciences, public policy, and business.

Anisotropic etching of silver nanoparticles for plasmonic structures capable of single-particle SERS.

The understanding of the localized surface plasmons (LSPs) that occur at the geometrically bounded surface of metal nanoparticles continues to advance as new and more complex nanostructures are found. It has been shown that the oscillation of electrons at the metal dielectric interface is strongly dependent on the size, symmetry, and proximity of nanoparticles. Here, we present a new method to chemically control the shape of silver nanocrystals by using a highly anisotropic etching process. Tuning of the etchant strength and reaction conditions allows the preparation of new nanoparticle shapes in high yield and purity, which cannot be synthesized with conventional nanocrystal growth methods. The etching process produces intraparticle gaps, which introduce modified plasmonic characteristics and significant scattering intensity in the near-infrared. These new silver particles serve as excellent substrates for wavelength-tunable, single-particle surface enhanced Raman spectroscopy (spSERS).

A nanocube plasmonic sensor for molecular binding on membrane surfaces.

Detection and characterization of molecular interactions on membrane surfaces is important to biological and pharmacological research. Here, silver nanocubes interfaced with glass-supported model membranes form a label-free sensor that measures protein binding to the membrane. The technique utilizes plasmon resonance scattering of nanocubes, which are chemically coupled to the membrane. In contrast to other plasmonic sensing techniques, this method features simple, solution-based device fabrication and readout. Static and dynamic protein/membrane binding are monitored and quantified.

Synthesis of bifunctional polymer nanotubes from silicon nanowire templates via atom transfer radical polymerization.

As a way to control the surface properties of nanowires and nanotubes, we present a method for growing polymer from the surface of silicon/silica core/shell nanowires. After modification of nanowire surfaces with polymer initiators, Atom Transfer Radical Polymerization (ATRP) was used to grow methacrylate polymer chains from the surface. The resulting structures were characterized by SEM, TEM, and EELS. After etching the silicon cores, the resulting polymer-coated nanotubes will have hydrophilic silica cores with hydrophobic polymer shells.