Nano-structural effects on Hematite (α-Fe2O3) nanoparticle radiofrequency heating.

Nano-sized hematite (α-Fe2O3) is not well suited for magnetic heating via an alternating magnetic field (AMF) because it is not superparamagnetic-at its best, it is weakly ferromagnetic. However, manipulating the magnetic properties of nano-sized hematite (i.e., magnetic saturation (Ms), magnetic remanence (Mr), and coercivity (Hc)) can make them useful for nanomedicine (i.e., magnetic hyperthermia) and nanoelectronics (i.e., data storage). Herein we study the effects of size, shape, and crystallinity on hematite nanoparticles to experimentally determine the most crucial variable leading to enhancing the radio frequency (RF) heating properties. We present the synthesis, characterization, and magnetic behavior to determine the structure-property relationship between hematite nano-magnetism and RF heating. Increasing particle shape anisotropy had the largest effect on the specific adsorption rate (SAR) producing SAR values more than 6 × greater than the nanospheres (i.e., 45.6 ± 3 W/g of α-Fe2O3 nanorods vs. 6.89 W/g of α-Fe2O3 nanospheres), indicating α-Fe2O3 nanorods can be useful for magnetic hyperthermia.

Influence of Oxygen-Containing Functional Groups on the Environmental Properties, Transformations, and Toxicity of Carbon Nanotubes.

Carbon nanotubes (CNTs) have unique physical and chemical properties that drive their use in a variety of commercial and industrial applications. CNTs are commonly oxidized prior to their use to enhance dispersion in polar solvents by deliberately grafting oxygen-containing functional groups onto CNT surfaces. In addition, CNT surface oxides can be unintentionally formed or modified after CNTs are released into the environment through exposure to reactive oxygen species and/or ultraviolet irradiation. Consequently, it is important to understand the impact of CNT surface oxidation on the environmental fate, transport, and toxicity of CNTs. In this review, we describe the specific role of oxygen-containing functional groups on the important environmental behaviors of CNTs in aqueous media (e.g., colloidal stability, adsorption, and photochemistry) as well as their biological impact. We place special emphasis on the value of systematically varying and quantifying surface oxides as a route to identifying quantitative structure-property relationships. The role of oxygen-containing functional groups in regulating the efficacy of CNT-enabled water treatment technologies and the influence of surface oxides on other carbon-based nanomaterials are also evaluated and discussed.

Quantitative Analysis of Nanorod Aggregation and Morphology from Scanning Electron Micrographs Using SEMseg.

General methods to achieve better physical insight about nanoparticle aggregation and assembly are needed because of the potential role of aggregation in a wide range of materials, environmental, and biological outcomes. Scanning electron microscopy (SEM) is fast and affordable compared to transmission electron microscopy, but SEM micrographs lack contrast and resolution due to lower beam energy, topographic contrast, edge effects, and charging. We present a new segmentation algorithm called SEMseg that is robust to the challenges inherent in SEM micrograph analysis and demonstrate its utility for analyzing gold (Au) nanorod aggregates. SEMseg not only supports nanoparticle size analysis for dispersed nanoparticles, but also discriminates between nanoparticles within an aggregate. We compare our algorithm to those incorporated into the commonly used software ImageJ and demonstrate improved segmentation of aggregate structures. New physical insight about aggregation is demonstrated by the introduction of an order parameter describing side-by-side structure in nanoparticle aggregates. We also present the segmentation and fitting algorithms included in SEMseg within a user-friendly graphical user interface. The resulting code is provided with an open-source interface to provide quantitative image processing tools for researchers to characterize both dispersed nanoparticles and nanoparticle assemblies in SEM micrographs with high throughput.

Photochemical Transformations of Carbon Dots in Aqueous Environments.

The unique physicochemical and luminescent properties of carbon dots (CDs) have motivated research efforts toward their incorporation into commercial products. Increased use of CDs will inevitably lead to their release into the environment where their fate and persistence will be influenced by photochemical transformations, the nature of which is poorly understood. This knowledge gap motivated the present investigation of the effects of direct and indirect photolysis on citric and malic acid-based CDs. Our results indicate that natural sunlight will rapidly and non-destructively photobleach CDs into optically inactive carbon nanoparticles. We demonstrate that after photobleaching, •OH exposure degrades CDs in a two-step process that will span several decades in natural waters. The first step, occurring over several years of •OH exposure, involves depolymerization of the CD structure, characterized by volatilization of over 60% of nascent carbon atoms and the oxidation of nitrogen atoms into nitro groups. This is followed by a slower oxidation of residual carbon atoms first into carboxylic acids and then volatile carbon species, while nitrogen atoms are oxidized into nitrate ions. Considered alongside related CD studies, our findings suggest that the environmental behavior of CDs will be strongly influenced by the molecular precursors used in their synthesis.

Nanoelectrode-emitter spectral overlap amplifies surface enhanced electrogenerated chemiluminescence.

Electrogenerated chemiluminescence (ECL) is a promising technique for low concentration molecular detection. To improve the detection limit, plasmonic nanoparticles have been proposed as signal boosting antennas to amplify ECL. Previous ensemble studies have hinted that spectral overlap between the nanoparticle antenna and the ECL emitter may play a role in signal enhancement. Ensemble spectroscopy, however, cannot resolve heterogeneities arising from colloidal nanoparticle size and shape distributions, leading to an incomplete picture of the impact of spectral overlap. Here, we isolate the effect of nanoparticle-emitter spectral overlap for a model ECL system, coreaction of tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate and tripropylamine, at the single-particle level while minimizing other factors influencing ECL intensities. We found a 10-fold enhancement of ECL among 952 gold nanoparticles. This signal enhancement is attributed exclusively to spectral overlap between the nanoparticle and the emitter. Our study provides new mechanistic insight into plasmonic enhancement of ECL, creating opportunities for low concentration ECL sensing.

Next-Generation Complex Metal Oxide Nanomaterials Negatively Impact Growth and Development in the Benthic Invertebrate Chironomus riparius upon Settling.

Most studies of nanomaterial environmental impacts have focused on relatively simple first-generation nanomaterials, including metals or metal oxides (e.g., Ag, ZnO) for which dissolution largely accounts for toxicity. Few studies have considered nanomaterials with more complex compositions, such as complex metal oxides, which represent an emerging class of next-generation nanomaterials used in commercial products at large scales. Importantly, many nanomaterials are not colloidally stable in aqueous environments and will aggregate and settle, yet most studies use pelagic rather than benthic-dwelling organisms. Here we show that exposure of the model benthic species Chironomus riparius to lithium cobalt oxide (Li xCo1- xO2, LCO) and lithium nickel manganese cobalt oxide (Li xNi yMn zCo1- y- zO2, NMC) at 10 and 100 mg·L-1 caused 30-60% declines in larval growth and a delay of 7-25 d in adult emergence. A correlated 41-48% decline in larval hemoglobin concentration and related gene expression changes suggest a potential adverse outcome pathway. Metal ions released from nanoparticles do not cause equivalent impacts, indicating a nanospecific effect. Nanomaterials settled within 2 days and indicate higher cumulative exposures to sediment organisms than those in the water column, making this a potentially realistic environmental exposure. Differences in toxicity between NMC and LCO indicate compositional tuning may reduce material impact.

Synthesis and Degradation of Cadmium-Free InP and InPZn/ZnS Quantum Dots in Solution.

This study advances the chemical research community toward the goal of replacing toxic cadmium-containing quantum dots (QDs) with environmentally benign InP QDs. The InP QD synthesis uniquely combines the previously reported use of InP magic-sized clusters (MSCs) as a single-source precursor for indium and phosphorus to form InP QDs, with zinc incorporation and subsequent ZnS shelling, to form InPZn/ZnS QDs with luminescence properties comparable to those of commonly used cadmium-containing luminescent QDs. The resulting InPZn/ZnS QDs have an emission quantum yield of about 50% across a broad range of emission peak wavelengths and emission peaks averaging 50 nm fwhm. The emission peak wavelength can be easily tuned by varying the Zn/In ratio in the reaction mixture. The strategy of using zinc stearate to tune the emission properties is advantageous as it does not lead to a loss of emission quantum yield or emission peak broadening. Although the initial optical properties of InP and InPZn/ZnS QDs are promising, thermal stability measurements of InPZn QDs show significant degradation in the absence of a shell compared to the CdSe QDs particularly at increased temperature in the presence of oxygen, which is indicative of thermal oxidation. There is no significant difference in the degradation rate of InP QDs made from molecular precursors and from MSCs. Additionally, the emission intensity and quantum yield of InPZn/ZnS QDs when purified and diluted in organic solvents under ambient conditions decrease significantly compared to those of CdSe/ZnS QDs. This indicates instability of the ZnS shell when prepared by common literature methods. This must be improved to realize high-quality, robust Cd-free QDs with the capability of replacing CdSe QDs in QD technologies.

Structure-Property Relationships of Amine-rich and Membrane-Disruptive Poly(oxonorbornene)-Coated Gold Nanoparticles.

The article describes the interactions between poly (oxonorbornenes) (PONs)-coated gold nanoparticles (AuNPs) with phospholipid vesicles and shows that the strength of these interactions strongly depends on the molecular structure of PONs, specifically their amine/alkyl side chain ratio. PONs, which are a recently introduced class of cationic polyelectrolytes, can be systematically varied to control the amine/alkyl ratio and to explore how the chemical character of cationic polyelectrolytes affects their interactions and the interactions of their nanoparticle conjugates with model membranes. Our study shows that increasing the amine/alkyl ratio by copolymerization of diamine and 1:1 amine/butyl oxonorbornene monomers impacts the availability of PONs amine/ammonium functional groups to interact with phospholipid membranes, the PONs surface coverage on AuNPs, and the membrane disruption activity of free PONs and PONs-AuNPs. The study makes use of transmission electron microscopy, UV-vis spectroscopy, dynamic light scattering, thermogravimetric analysis, fluorescamine assay, ζ-potential measurements, and X-ray photoelectron spectroscopy measurements to characterize the PONs-AuNPs' size, size distribution, aggregation state, surface charge, and PONs surface coverage. The study also makes use of real-time fluorescence measurements of fluorescent liposomes before and during exposure to free PONs and PONs-AuNPs to determine the membrane disruption activity of free PONs and PONs-AuNPs. As commonly observed with cationic polyelectrolytes, both free PONs and PONs-AuNPs display significant membrane disruption activity. Under conditions where the amine/alkyl ratio in PONs maximizes PONs surface coverage, the membrane disruption activity of PONs-AuNPs is about 10-fold higher than the membrane disruption activity of the same free PONs. This is attributed to the increased local concentration of ammonium ions when PONs-AuNPs interact with the liposome membranes. In contrast, the hydrophobicity of amine-rich PONs, which are made for example from diamine oxonorbornene monomers, is significantly reduced. This leads to a significant reduction of PON surface coverage on AuNPs and in turn to a significant decrease in membrane disruption.

Comparing postdeposition reactions of electrons and radicals with Pt nanostructures created by focused electron beam induced deposition.

The ability of electrons and atomic hydrogen (AH) to remove residual chlorine from PtCl2 deposits created from cis-Pt(CO)2Cl2 by focused electron beam induced deposition (FEBID) is evaluated. Auger electron spectroscopy (AES) and energy-dispersive X-ray spectroscopy (EDS) measurements as well as thermodynamics calculations support the idea that electrons can remove chlorine from PtCl2 structures via an electron-stimulated desorption (ESD) process. It was found that the effectiveness of electrons to purify deposits greater than a few nanometers in height is compromised by the limited escape depth of the chloride ions generated in the purification step. In contrast, chlorine atoms can be efficiently and completely removed from PtCl2 deposits using AH, regardless of the thickness of the deposit. Although AH was found to be extremely effective at chemically purifying PtCl2 deposits, its viability as a FEBID purification strategy is compromised by the mobility of transient Pt-H species formed during the purification process. Scanning electron microscopy data show that this results in the formation of porous structures and can even cause the deposit to lose structural integrity. However, this phenomenon suggests that the use of AH may be a useful strategy to create high surface area Pt catalysts and may reverse the effects of sintering. In marked contrast to the effect observed with AH, densification of the structure was observed during the postdeposition purification of PtC x deposits created from MeCpPtMe3 using atomic oxygen (AO), although the limited penetration depth of AO restricts its effectiveness as a purification strategy to relatively small nanostructures.