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We use photocatalytic reduction to synthesize mono and bimetallic nanoparticles. This approach reveals a new formation pathway involving continuous nucleation and allows the reaction to be turned on and off without impacting particle outcomes.

The diffusion of poly(ethylene glycol) methyl ether thiol (PEGSH)-functionalized gold nanoparticles (NPs) was measured in polyacrylamide gels with various cross-linking densities. The molecular weight of the PEGSH ligand and particle core size were both varied to yield particles with hydrodynamic diameters ranging from 7 to 21 nm. The gel mesh size was varied from approximately 36 to 60 nm by controlling the cross-linking density of the gel. Because high-molecular-weight ligands are expected to yield more compressible particles, we expected the diffusion constants of the NPs to depend on their hard/soft ratios (where the hard component of the particle consists of the particle core and the soft component of the particle consists of the ligand shell). However, our measurements revealed that NP diffusion coefficients resulted primarily from changes in the overall hydrodynamic diameter and not the ratio of particle core size to ligand size. Across all particles and gels, we found that the diffusion coefficient was well predicted by the confinement ratio calculated from the diameter of the particle and an estimate of the gel mesh size obtained from the elastic blob model and was well described using a hopping model for nanoparticle diffusion. These results suggest that the elastic blob model provides a reasonable estimate of the mesh size that particles "see" as they diffuse through the gel. This work brings new insights into the factors that dictate how NPs move through polymer gels and will inform the development of hydrogel nanocomposites for applications such as drug delivery in heterogeneous, viscoelastic biological materials.

Unlike conventional antimicrobials, the study of bacterial resistance to silver nanoparticles (AgNPs) remains in its infancy and the mechanism(s) through which it evolves are limited and inconclusive. The central question remains whether bacterial resistance is driven by the AgNPs, released Ag(I) ions or a combination of these and other factors. Here, we show a specific resistance in an Escherichia coli K-12 MG1655 strain to subinhibitory concentrations of AgNPs, and not Ag(I) ions, as indicated by a statistically significant greater-than-twofold increase in the minimum inhibitory concentration occurring after eight repeated passages that was maintained after the AgNPs were removed and reintroduced. Whole-population genome sequencing identified a cusS mutation associated with the heritable resistance that possibly increased silver ion efflux. Finally, we rule out the effect of particle aggregation on resistance and suggest that the mechanism of resistance may be enhanced or mediated by flagellum-based motility. Bacterial motility may be used as an important predictor of whether a particular bacteria strain can develop AgNP resistance and could inform design of nanoenabled antimicrobials that mechanistically target specific types of bacteria.

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...

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.

Nanoparticle superstructures have received widespread interest due to their unique physical properties that derive from the size, shape, composition, and 3D assembly of their component nanoparticle building blocks. Successful deployment of these materials for target applications requires methods for modifying their surfaces to impart specific properties and functions. To this end, we demonstrate that ligand exchange processes, which are extensively employed for functionalizing discrete nanoparticles, can be used to modify the surfaces of nanoparticle superstructures. We show that peptides coating the external surfaces of hollow, spherical gold nanoparticle superstructures are effectively exchanged with thiolated ligands, while maintaining the integrity of the assembled structure. The resulting superstructures are stable on the bench. These proof-of-principle studies highlight the potential of using ligand exchange to differentiate nanoparticle superstructures, thereby expanding their utility and application scope.

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.

In biological systems, chemical and physical transformations of engineered silver nanomaterials (AgENMs) are mediated, in part, by proteins and other biomolecules. Metalloprotein interactions with AgENMs are also central in understanding toxicity and antimicrobial and resistance mechanisms. Despite their readily available thiolate and amine ligands, zinc finger (ZF) peptides have thus far escaped study in reaction with AgENMs and their Ag(I) oxidative dissolution product. We report spectroscopic studies that characterize AgENM and Ag(I) interactions with two ZF peptides that differ in sequence, but not in metal binding ligands: the ZF consensus peptide CP-CCHC and the C-terminal zinc finger domain of HIV-1 nucleocapsid protein p7 (NCp7_C). Both ZF peptides catalyze AgENM (10 and 40 nm, citrate coated) dissolution and agglomeration, two important AgENM transformations that impact bioreactivity. AgENMs and their oxidative dissolution product, Ag(I)(aq), mediate changes to ZF peptide structure and metalation as well. Spectroscopic titrations of Ag(I) into apo-ZF peptides show an Ag(I)-thiolate charge transfer band, indicative of Ag(I)-ZF binding. Fluorescence studies of the Zn(II)-NCp_7 complex indicate that the Ag(I) also effectively competes with the Zn(II) to drive Zn(II) displacement from the ZFs. Upon interaction with AgENMs, Zn(II) bound ZF peptides show a secondary structural change in circular dichroism spectroscopy toward an apo-like structure. The results suggest that Ag(I) and AgENMs may alter ZF protein function within the cell.

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

Amphiphilic triblock copolymers containing Fe(III) -catecholate complexes formulated as spherical- or cylindrical-shaped micellar nanoparticles (SMN and CMN, respectively) are described as new T1-weighted agents with high relaxivity, low cytotoxicity, and long-term stability in biological fluids. Relaxivities of both SMN and CMN exceed those of established gadolinium chelates across a wide range of magnetic field strengths. Interestingly, shape-dependent behavior is observed in terms of the particles' interactions with HeLa cells, with CMN exhibiting enhanced uptake and contrast via magnetic resonance imaging (MRI) compared with SMN. These results suggest that control over soft nanoparticle shape will provide an avenue for optimization of particle-based contrast agents as biodiagnostics. The polycatechol nanoparticles are proposed as suitable for preclinical investigations into their viability as gadolinium-free, safe, and effective imaging agents for MRI contrast enhancement.

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...

A Gd3+-coordinated polymerizable analogue of the MRI contrast agent Gd-DOTA was used to prepare amphiphilic block copolymers, with hydrophilic blocks composed entirely of the polymerized contrast agent., A Gd3+-coordinated polymerizable analogue of the MRI contrast agent Gd-DOTA was used to prepare amphiphilic block copolymers, with hydrophilic blocks composed entirely of the polymerized contrast agent. The resulting amphiphilic block copolymers assemble into nanoparticles (NPs) of spherical- or fibril-shape, each demonstrating enhanced relaxivity over Gd-DOTA. As an initial examination of their behavior in vivo, intraperitoneal (IP) injection of NPs into live mice was performed, showing long IP residence times, observed by MRI. Extended residence times for particles of well-defined morphology may represent a valuable design paradigm for treatment or diagnosis of peritoneal malignances.

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.

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.

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.

In this paper we present in situ transmission electron microscopy of synthetic polymeric nanoparticles with emphasis on capturing motion in a solvated, aqueous state. The nanoparticles studied were obtained from the direct polymerization of a Pt(II)-containing monomer. The resulting structures provided sufficient contrast for facile imaging in situ. We contend that this technique will quickly become essential in the characterization of analogous systems, especially where dynamics are of interest in the solvated state. We describe the preparation of the synthetic micellar nanoparticles together with their characterization and motion in liquid water with comparison to conventional electron microscopy analyses. © 2014 American Chemical Society.

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).

D-band position is often used to describe the reactivity of alloy catalysts. However, the spatial separation (dispersion) and geometric arrangement of catalytically active surface atoms can also control the system’s overall reactivity. My talk will discuss how the dispersion of catalytically active Rh atoms within 2-3 nm, ligand-protected Au/Rh alloy nanoparticles directly impacts electrocatalytic H2 oxidation reaction (HOR) activity. The HOR is an interesting model reaction for the Au/Rh system because Rh atoms catalyze H2 oxidation, whereas Au atoms do not. This provides the opportunity to study the composition-dependent evolution of HOR activity as a function of alloy composition (0-100% Rh). We find that HOR activity follows a volcano-type trend. Pure Au particles do not oxidize H2, and peak HOR activity was found for particles containing 21% and 34% Rh. Beyond this optimum Rh content the HOR activity decreased towards that of 100% Rh particles and a commercially available Rh/C catalyst. In fact, HOR activity decreased as a function of (%Rh)-1 beyond peak activity. We rationalize this trend through the dispersion of Rh-containing active sites on the surface of the Au/Rh alloy NPs. Analysis of literature results has identified similar inverse relationships between catalytic activity and composition. First-principles density functional theory (DFT) studies were also used to model H-binding at realistic Au/Rh alloy nanoparticles. H-binding energy is a common metric for predicting HOR activity. We found that Rh incorporation increased the d-band position of Rh containing particles compared with Au. However, did could not identify any relationship between H-biding and d-band energy. These results are in contrast to what would be expected from a purely electronic d-band model, and they provide strong evidence that intra-particle active site dispersion can tune the catalytic activity of alloy nanocatalysts. We hypothesize this phenomenon should also extend to other alloy systems, and active site dispersion provides another tool for controlling the nano-scale chemistry of electrocatalysts.

Au(core)-Ag(shell) triangular bifrustum nanocrystals were synthesized in aqueous solution using a seed-mediated approach. The formation of the Ag layer on the Au nanoprism seeds leads to structures with highly tunable dipole and quadrupole surface plasmon resonances. Discrete dipole approximation calculations show that it is the geometry of these novel structures rather than the addition of a new element that leads to the plasmon tunability. The structure and composition of these novel nanocrystals have been investigated by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and energy-dispersive spectrometry.

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.

Two-component triblock magnetic nanorods with gold end blocks and nickel interior blocks have been synthesized and used as affinity templates for the simultaneous and efficient separation of a three-component protein mixture. The gold blocks were selectively functionalized with 11-amino-1-undecanethiol, and then glutaraldehyde was used to covalently attach nitrostreptavidin to them. His-tagged proteins bind to the nickel block and biotin-tagged proteins bind to the functionalized gold ends, allowing one to separate a mixture of three proteins with a single material. Each surface-bound protein can be released selectively using imidazole for the His-tagged protein and biotin for the biotinylated protein.

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.