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Using a newly designed and developed parallelized photoreactor and colorimetric detection method, a large sampling of bimetallic cocatalysts (Pd/Sn, Pd/Mo, Pd/Ru, Pd/Pb, Pd/Ni, Ni/Sn, Mo/Sn, and Pt...

There is significant interest in earth-abundant plasmonic materials, but whether or not their performance can match or even surpass their noble metal counterparts remains to be established. An impo...

Controlling both the concentration and the distribution of elements in a given material is often crucial to extracting and optimizing synergistic properties of the various constituents. An interesting class of such multielement materials is metal chalcogenide nanoparticles, which exhibit a wide range of composition-dependent optoelectronic properties including both bandgap-mediated processes and localized surface plasmon resonance properties, each of which is useful in applications ranging from energy conversion to sensing. Because metal chalcogenide nanoparticles can support several different metal elements in a variety of chalcogen lattices, this material class has particularly benefited from the ability to control both atom concentration and atom arrangement to tailor final particle properties. The primary method to access complex, multimetallic chalcogenide particles is via a postsynthetic cation exchange strategy. One-pot syntheses have been less explored to access these complex particles, although t...

Rare earth elements (REEs) are strategically important for national security and advanced technologies. Consequently, significant effort has been devoted towards increasing REE domestic production, including the extraction of REEs from coal, coal combustion byproducts, and their associated waste streams such as acid mine drainage. Analytical techniques for rapid quantification of REE content in aqueous phases can facilitate REE recovery through rapid identification of high-value waste streams. In this work, we show that BioMOF-100 can be used as a fluorescent-based sensitizer for emissive REE ion detection in water, providing rapid (10 min) analysis times and sensitive detection (parts-per-billion detection limits) for terbium, dysprosium, samarium, europium, ytterbium, and neodymium, even in the presence of acids or secondary metals.

Polyelemental nanoparticles (PE NPs) containing four or more elements in a single NP have intriguing intrinsic properties compared to their single-element counterparts. The fusion of diverse elements induces synergistic effects including new physical and chemical phenomena. However, conventional methods have not offered effective strategies for the uniform creation of PE NPs with high reproducibility. Recently, with advances in nanoscience, several new methods have been developed using both thermodynamic and kinetic approaches and, often, the interplay between them. In this Perspective, we highlight recent key advances in the design of PE NPs and their underlying formation mechanisms. We discuss the potential applications of PE NPs and the outlook and future directions for this field.

At all length scales, the stability of materials is impacted by their surrounding environment. However, it has now been observed that materials with different dimensions can exhibit markedly different responses to their environment, even for the same material composition. For example, the deterioration of nanomaterials is complicated by the unique chemical and physical properties that arise from changes to their size, shape, and/or surface chemistry. A first step in understanding and predicting nanomaterial stabilities is to leverage the decades of work dedicated to understanding the environment-specific deterioration mechanisms of analogous bulk materials. Then, unique nanoscale properties can be accounted for and used to understand both similarities and differences in deterioration behavior across these length scales. In this review, we specifically consider the stability of group 11 coinage metal surfaces: copper, silver, and gold. We first summarize the chemical mechanisms of environmentally-driven deterioration of these metals in the bulk. We then apply this knowledge to interpret stability studies of nanoparticles made from the same elements. Ultimately, we find that while the reactivity of gold and copper is relatively consistent across length scales, the composition of products formed on silver surfaces differs significantly. These results have important implications for predicting and controlling both desirable and undesirable metal nanoparticle deterioration processes.

The recent ExecutiveOrder by President Trump attempting to ban temporarily the citizens of seven countries (Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen) from entering the United States is having significant consequences within the country and around the world. The Order poses a threat to the health and vitality of science, barring students and scientists from these countries from traveling to the United States to study or to attend conferences. In preventing those members of the international scientific community from traveling beyond U.S. borders without guaranteed safe return, the Executive Order demeans them; in so doing, it demeans us all. Universities and research communities are especially impacted, as major universities have students and often faculty holding passports from one of these seven countries. This temporary ban would affect refugees fleeing war-torn areas, challenging the long-standing notion that the United States is a safe haven for those fleeing persecution and war in addition to being a magnet for talent from every corner of the world. The pages of this journal reflect the geographic, ethnic, and cultural diversity that underpins great science. The ban impacts domestic and global scientific efforts and communities. Science succeeds through the cooperation between collections of individuals and teams around the world discovering and learning from each other. To ensure rapid scientific progress, open communication and exchange between scientists are essential. As scientists, engineers, and clinicians, we have benefited from open interactions and collaborations with visitors and students from all parts of the world as well as through scientific publications and discussions at scientific meetings.

The syntheses, properties, and broad utility of noble metal plasmonic nanomaterials are now well-established. To capitalize on this exceptional utility, mitigate its cost, and potentially expand it, non-noble metal plasmonic materials have become a topic of widespread interest. As new plasmonic materials come online, it is important to understand and assess their ability to generate comparable or complementary plasmonic properties to their noble metal counterparts, including as both sensing and photoredox materials. Here, we study plasmon-driven chemistry on degenerately doped copper selenide (Cu2–xSe) nanoparticles. In particular, we observe plasmon-driven dimerization of 4-nitrobenzenethiol to 4,4′-dimercaptoazobenzene on Cu2–xSe surfaces with yields comparable to those observed from noble metal nanoparticles. Overall, our results indicate that doped semiconductor nanoparticles are promising for light-driven chemistry technologies.

Catalytic and optical properties can be coupled by combining different metals into nanoscale architectures in which both the shape and the composition provide fine-tuning of functionality. Here, discrete, small Pt nanoparticles (diameter = 3-6 nm) were grown in linear arrays on Au nanoprisms, and the resulting structures are shown to retain strong localized surface plasmon resonances. Multidimensional electron microscopy and spectroscopy techniques (energy-dispersive X-ray spectroscopy, electron tomography, and electron energy-loss spectroscopy) were used to unravel their local composition, three-dimensional morphology, growth patterns, and optical properties. The composition and tomographic analyses disclose otherwise ambiguous details of the Pt-decorated Au nanoprisms, revealing that both pseudospherical protrusions and dendritic Pt nanoparticles grow on all faces of the nanoprisms (the faceted or occasionally twisted morphologies of which are also revealed), and shed light on the alignment of the Pt nanoparticles. The electron energy-loss spectroscopy investigations show that the Au nanoprisms support multiple localized surface plasmon resonances despite the presence of pendant Pt nanoparticles. The plasmonic fields at the surface of the nanoprisms indeed extend into the Pt nanoparticles, opening possibilities for combined optical and catalytic applications. These insights pave the way toward comprehensive nanoengineering of multifunctional bimetallic nanostructures, with potential applications in plasmon-enhanced catalysis and in situ monitoring of chemical processes via surface-enhanced spectroscopy.

Author(s): Chan, WCW; Chhowalla, M; Farokhzad, O; Glotzer, S; Gogotsi, Y; Hammond, PT; Hersam, MC; Javey, A; Kagan, CR; Kataoka, K; Khademhosseini, A; Kotov, NA; Lee, ST; Lee, YH; Li, Y; Millstone, JE; Mulvaney, P; Nel, AE; Nordlander, PJ; Parak, WJ; Penner, RM; Rogach, AL; Schaak, RE; Sood, AK; Stevens, MM; Wee, ATS; Weil, T; Grant Willson, C; Weiss, PS

Solution phase noble metal nanoparticle growth reactions are comprised of deceptively simple steps. Analytical methods with high chemical, spatial, and temporal resolution are crucial to understanding these reactions and subsequent nanoparticle properties. However, approaches for the characterization of solid inorganic materials and solution phase molecular species are often disparate. One powerful technique to address this gap is nuclear magnetic resonance (NMR) spectroscopy, which can facilitate routine, direct, molecular-scale analysis of nanoparticle formation and morphology in situ, in both the solution and the solid phase. A growing body of work indicates that NMR analyses should yield an exciting complement to the existing canon of routine nanoparticle characterization methods such as electron microscopy and optical absorption spectroscopy. Here, we discuss recent developments in the application of NMR techniques to the study of noble metal nanoparticle growth, surface chemistry, and physical prope...

We report the use of gold nanoparticle surface chemistry as a tool for site-selective noble metal deposition onto colloidal gold nanoparticle substrates. Specifically, we demonstrate that partial passivation of the gold nanoparticle surface using thiolated ligands can induce a transition from linear palladium island deposition to growth of palladium selectively at plasmonic hotspots on the edges or vertices of the underlying particle substrate. Further, we demonstrate the broader applicability of this approach with respect to substrate morphology (e.g., prismatic and rod-shaped nanoparticles), secondary metal (e.g., palladium, gold, and platinum), and surface ligand (e.g., surfactant molecules and n-alkanethiols). Taken together, these results demonstrate the important role of metal–ligand surface chemistry and ligand packing density on the resulting modes of multimetallic nanoparticle growth, and in particular, the ability to direct that growth to particle regions of impact such as plasmonic hotspots.

We demonstrate the synthesis of discrete, composition-tunable gold-cobalt nanoparticle alloys (% Co = 0–100%; diameter = 2–3 nm), in contrast with bulk behavior, which shows immiscibility of Au and Co at room temperature across all composition space. These particles are characterized by transmission electron microscopy and 1H NMR techniques, as well as inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. In particular, 1H NMR methods allow the simultaneous evaluation of composition-tunable magnetic properties as well as molecular characterization of the colloid, including ligand environment and hydrodynamic diameter. These experiments also demonstrate a route to optimize bimodal imaging modalities, where we identify AuxCoyNP compositions that exhibit both bright NIR emission (2884 m −1cm−1) as well as some of the highest per-particle T 2 relaxivities (12200 mm NP −1s−1) reported to date for this particle size range.

Seedless initiation has been used as a simple and sustainable alternative to seed-mediated production of two canonical anisotropic gold nanoparticles: nanorods and nanoprisms. The concentration of reducing agent during the nucleation event was found to influence the resulting product morphology, producing nanorods with lengths from 30 to 630 nm and triangular or hexagonal prisms with vertex-to-vertex lengths ranging from 120 to over 700 nm. The seedless approach is then used to eliminate several chemical reagents and reactions steps from classic particle preparations while achieving almost identical nanoparticle products and product yields. Our results shed light on factors that influence (or do not influence) the evolution of gold nanoparticle shape and present a dramatically more efficient route to obtaining these architectures. Specifically, using these methods reduces the total amount of reagent needed to produce nanorods and nanoprisms by as much as 90 wt % and, to the best of our knowledge, has yielded the first report of spectroscopically discernible, colloidal gold nanoplates synthesized using a seedless methodology.

Here, we use solution and solid-state (31)P NMR to study the ligand environment of water soluble, phosphine-terminated gold nanoparticles. The resulting spectra indicate that particle-bound phosphine ligands occupy an unexpectedly monodisperse ligand environment. This uniformity then facilitates one of the first descriptions of distinct (31)P-(197)Au coupling in colloidal nanoparticles.

Efficient organic photovoltaic (OPV) materials are constructed by attaching completely planar, symmetric end-groups to donor-acceptor electroactive small molecules. Appending C2-pyrene as the small molecule end-group to a diketopyrrolopyrrole core leads to materials with a tight, aligned crystal packing and favorable morphology dictated by π-π interactions, resulting in high power conversion efficiencies and high fill factors. The use of end-groups to direct molecular self-assembly is an effective strategy for designing high-performance small molecule OPV devices.

Semiconducting polymer nanoparticles have attracted increasing interest for the facile fabrication of organic electronic devices. These nanoparticles could provide the ability to control thin film morphology independently of optical and electronic properties. Using poly(3-hexylthiophene), we demonstrate surfactant-free synthesis and characterization of size-controlled, semicrystalline polymer nanoparticles. Our method produces discrete nanoparticles that can be deposited from solution into thin films. By controlling the molecular weight, polydispersity, and regioregularity of the polymer as well as varying its initial solution concentration, we tune both the size and crystallinity of the resulting nanoparticles. Organic field effect transistors (OFETs) using nanoparticles made from this method produce good semiconducting devices with hole mobilities on the order of 10(-3) cm(2)/(V s). This approach to forming polymer nanoparticles is attractive for the introduction of solution-processable, well-characterized nanoscale crystalline domains of a variety of conjugated polymers and should be useful for the fabrication and optimization of organic electronic devices.

The synthesis of silica-encapsulated gold nanoprisms (AuNP@SiO2) is reported. These nanostructures are remarkably stable and resist etching and rounding of their sharp vertices (a process which begins on unprotected Au nanoprisms in a matter of hours) in many chemical environments (water, ethanol, dimethyl sulfoxide, and tetrahydrofuran). The silica growth process has been studied and occurs according to the shape of the particle, where the edges of the prisms are coated less than the large triangular facets. The AuNP@SiO2 particles have dielectric sensitivities that are as large as 737 nm/RIU. Discrete dipole approximation calculations have been used to investigate the effects of this variable thickness on dielectric sensitivity and show that for the anisotropic coatings it is significantly higher than for a uniform coating due to the location of electromagnetic hot spots near the tips and edges of the particles. These calculations also show that dipole resonances exhibit greater sensitivity than multipo...

Over the past two decades, there has been an enormous effort to understand, control, and use the relationship between the morphology of nanomaterials and their physical and chemical properties.[1,2] Indeed, a great deal of effort has focused on controlling the size, shape, and composition of nanostructures. However, equally important is the surface chemistry of such structures, especially when one considers that the ratio of surface to bulk atoms is much higher than that in micro- or macroscopic systems. For example, the surface plasmon resonances (SPRs) of nanoparticles are highly dependent upon the dielectric medium that surrounds them, including adlayers of molecules and solvent.[3,4] Catalytic activity of a nanoparticle is also highly dependent upon adsorbate.[5,6] Indeed, the development of ways to control the structure and chemical functionalization of a nanoparticle surface is a major area of research, and has led to the discovery of new properties and applications for this important class of materials.[7] In the case of isotropic metal nanoparticles, functionalization has led to a variety of exciting scientific insights and applications, including the use of nanoparticles for spectroscopic labels,[8] gene-regulation agents,[9] and ultrasensitive biodiagnostic tools.[10] In general, less has been done with anisotropic structures, but there have been some important observations and advances made for nanorod and nanoshell structures.[11–14] For example, Gole and Murphy have reported that gold nanorods functionalized with biotin-disulfide will assemble in an end-to-end manner when interconnecting streptavidin proteins are added to a colloid containing them. The authors concluded that such assembly behavior was indicative of end-selective functionalization.[12] Mann and co-workers described a similar example with oligonucleotide-modified nanorods, but in contrast with the Murphy system, they observe sheet-like assembly of nanorods along their long axes.[11] These results present a challenge to both understand and establish control over the face-selective functionalization of anisotropic nanoparticles.

The cellular internalization of oligonucleotide-modified nanoparticles is investigated. Uptake is dependent on the density of the oligonucleotide loading on the surface of the particles, where higher densities lead to greater uptake. Densely functionalized nanoparticles adsorb a large number of proteins on the nanoparticle surface. Nanoparticle uptake is greatest where a large number of proteins are associated with the particle.

Energy transfer from plasmonic nanoparticles to semiconductors can expand the available spectrum of solar energy-harvesting devices. Here, we spatially and spectrally resolve the interaction between single Ag nanocubes with insulating and semiconducting substrates using electron energy-loss spectroscopy, electrodynamics simulations, and extended plasmon hybridization theory. Our results illustrate a new way to characterize plasmon–semiconductor energy transfer at the nanoscale and bear impact upon the design of next-generation solar energy-harvesting devices.

A straightforward method is investigated for controlling and reinitiating the growth of single-crystalline Au nanoprisms. This work is based on seeding methodology, and depends on the slow reduction of metal ions onto the surface of a growing nanoprism. In this manner, we can tailor the edge length of Au nanoprisms between 100 and 300 nm without changing their thickness or crystallinity. Each nanoprism size has been characterized by UV-vis-NIR (NIR: near-IR) spectroscopy, transmission electron microscopy (TEM) techniques, and statistical analysis. Based on this work and existing silver halide crystal-growth theories, a preliminary mechanism is proposed which comments on the interplay between crystal growth and surface chemistry that ultimately dictates the morphology of the resulting nanostructure.

Very long range surface-enhanced Raman scattering is observed from a nickel nanowire that is separated by 120 nm from a pair of gold nanodisks. The excitation of the surface-plasmon resonance (SPR) from the gold nanodisk pair generates an enhanced electromagnetic field near the nickel segment (SEM, left), leading to Raman intensity greater than the nickel alone (right).

The next step in the maturing field of nanotechnology is to develop ways to introduce unusual architectural changes to simple building blocks. For nanowires, on-wire lithography (OWL) has emerged as a powerful way of synthesizing a segmented structure and subsequently introducing architectural changes through post-chemical treatment. In the OWL protocol presented here, multisegmented nanowires are grown and a support layer is deposited on one side of each nanostructure. After selective chemical etching of sacrificial segments, structures with gaps as small as 2 nm and disks as thin as 20 nm can be created. These nanostructures are highly tailorable and can be used in electrical transport, Raman enhancement and energy conversion. Such nanostructures can be functionalized with many types of adsorbates, enabling the use of OWL-generated structures as bioactive probes for diagnostic assays and molecular transport junctions. The process takes 13–36 h depending on the type of adsorbate used to functionalize the nanostructures.

It is now well-known that the size, shape, and composition of nanomaterials can dramatically affect their physical and chemical properties, and that technologies based on nanoscale materials have the potential to revolutionize fields ranging from catalysis to medicine. Among these materials, anisotropic particles are particularly interesting because the decreased symmetry of such particles often leads to new and unusual chemical and physical behavior. Within this class of particles, triangular Au and Ag nanoprisms stand out due to their structure- and environment-dependent optical features, their anisotropic surface energetics, and the emergence of reliable synthetic methods for producing them in bulk quantities with control over their edge lengths and thickness. This Review will describe a variety of solution-based methods for synthesizing Au and Ag triangular prismatic structures, and will address and discuss proposed mechanisms for their formation.

Research on surface-enhanced Raman spectroscopy (SERS) is an area of intense interest because the technique allows one to probe small collections of, and in certain cases, individual molecules using relatively straightforward spectroscopic techniques and nanostructured substrates. Researchers in this area have attempted to develop many new technological innovations including high sensitivity chemical and biological detection systems, labeling schemes for authentication and tracking purposes, and dual scanning-probe/spectroscopic techniques that simultaneously provide topographical and spectroscopic information about an underlying surface or nanostructure. However, progress has been hampered by the inability of researchers to fabricate substrates with the high sensitivity, tunability, robustness, and reproducibility necessary for truly practical and successful SERS-based systems. These limitations have been due in part to a relative lack of control over the nanoscale features of Raman substrates that are responsible for the enhancement. With the advent of nanotechnology, new approaches are being developed to overcome these issues and produce substrates with higher sensitivity, stability, and reproducibility. This tutorial review focuses on recent progress in the design and fabrication of substrates for surface-enhanced Raman spectroscopy, with an emphasis on the influence of nanotechnology.