Women in Nanotechnology: Toward Better Materials through a Better

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Women in Nanotechnology: Toward Better Materials through a Better Understanding of Low-Dimensional Systems

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anotechnology impacts many important areas, such as optoelectronics, energy, biology, and medicine, to name a few.1−4 Advances in nanoscience increase our knowledge of materials on the submicroscale, particularly their fundamental physical, chemical, and biological properties that are different from the bulk counterparts. Through improved understanding of these nanoscale properties, scientists and engineers will be able to control individual atoms and molecules effectively on demand and thus will be able to manufacture next-generation materials for a better future.5 This virtual issue is appearing during the 256th ACS National Meeting, which is being held in Boston on August 19−23, 2018 and centers on the theme “Nanoscience, Nanotechnology & Beyond”.6 In this virtual issue, we highlight the work of research groups led by women investigators worldwide in a celebration of their contributions to excellent science. Work led by female investigators continues to increase, and we aim to introduce some of those exciting nanotechnology projects. Many of the research topics featured are being presented concurrently at the “Women in Nanotechnology” symposium at the ACS National Meeting. This symposium is co-sponsored by the journals Nano Letters, ACS Nano, and Chemistry of Materials and by the Division of Inorganic Chemistry and the Women Chemists Committee.

Figure 1. Recent nanotechnology projects led by women researchers. Reprinted from refs 7, 13, 16, 18, 28, and 32. Copyrights 2017, 2018, 2015, 2016, 2018, and 2018, respectively, American Chemical Society.

temperatures and I concentrations. They observed products such as Bi2S3, BiSI, and Bi13S18I2 and identified formation of subvalent Bi24+ dimers in Bi13S18I2, which led to more accurate assignments of the disordered Bi sites in the structure.8 A mechanistic study on the nucleation pathway for α-Zn3P2 nanoparticles undertaken by Prof. Brandi Cossairt and her coworkers indicates that the use of P(SiMe3)3 as the phosphorus precursor results in the formation of the intermediate [EtZnP(SiMe2)3]. The latter is not very reactive and leads to fewer nuclei and thus larger particles with improved crystallinity, compared to other known methods for the formation of these nanoparticles.9 The area of gold and gold-containing nanoparticles is also an active area of research. At Indiana University, Prof. Sara Skrabalak and her collaborators formulated a strategy to break symmetry in the seeded growth of platonic metal nanocrystals, which can be applied for bottom-up syntheses of nanomaterials. They achieved regioselective deposition of various Pt/Au and Pd/Au nanocrystals at low supersaturation by capitalizing on a kinetic preference for high-energy defect-rich sites over lower-energy sites.10 Prof. Xing Yi Ling’s group at Nanyang Technological University in Singapore developed bimetallic nanomaterials of Pt-nanoporous Au bowls. They exploited the weakened binding strength between Pt and intermediate poisoning species, which originated from the d-band electronic structure

In this virtual issue, we highlight the work of research groups led by women investigators worldwide in a celebration of their contributions to excellent science. The articles featured in this virtual issue cover a wide range of topics, from synthesis, to property prediction and measurement, to applications and device fabrication (Figure 1). The technological impacts of these studies reach many fields including energy, catalysis, optoelectronics, photonics, and biomedicine. Hence, they represent the incredible breadth and depth of exciting work in nanoscience and nanotechnology. In the area of synthesis and control of properties in the nanoregime, Prof. Delia Milliron at the University of Texas at Austin and her collaborators fabricated mesoporous WOxNbOx composite films on flexible substrates for the selective control of visible and near-infrared light transmittance. The optical-quality mesoporous films were created through a simple, template- and annealing-free strategy using ligandstripped, charge-stabilized dispersion of naked anisotropic nanocrystals.7 Prof. Susan Latturner’s group at Florida State University investigated reactions of Bi in S/I flux mixtures at various © XXXX American Chemical Society

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to the tunable and fully controlled formation of oligomeric chains. This process mimics the organization of protein-like filaments and results in materials with an array of ultrastructures and properties similar to natural fibers.19 Much work has been done in the cellular domain, as well. To elicit a high level of messenger RNA (mRNA) transfection in different cell types, Prof. Paula Hammond and her collaborators at MIT developed nanoplexes. They achieved enhanced mRNA transfection by adjusting the nanoscale distance between the mRNA strand and the eukaryotic initiation factor 4E (eIF4B) protein inside the nanosized complex.20 While studying nanoarticle-mediated signaling RNA (siRNA) delivery, Prof. Danielle Benoit and her team at the University of Rochester evaluated the effects of biological fluids on the stability of the nanoparticle−siRNA complex. They discovered that the complexes aggregate in serum-containing buffer but are stable in serum-free media, which leads to improved siRNA uptake in vitro and more highly efficient gene silencing.21 Membranes and related structures have also been studied for diverse applications. Prof. Gang-yu Liu at the University of California, Davis, and her collaborators created nanoring arrays from a hapten of 2,4-dinitrophyenyl (DNP) molecules that enable the formation of membrane nanotubes among rat basophilic leukemia (RBL) cells. The team showed that engineered nanostructures can be used to activate or to inhibit desired cellular signaling cascades selectively.22 By coating porous supports with arrays of polymer micelles in alcohol, Prof. Ahyse Asatekin’s research team at Tufts University developed membranes with 1−3 nm carboxylatefunctionalized charged nanochannels. These nanochannels enabled separation of organic molecules of similar sizes but different charges. They showed that neutral solutes permeate several orders of magnitude faster than charged compounds, with water fluxes comparable to those of commercial membranes.23 Prof. Maria Hoernke at the University of Freiburg in Germany, with her international collaborators, compared two effective protocols used to study model membrane leakage. The research team reconciled apparent discrepancies between the two assay methods, fluorescence microscopy versus fluorescence lifetime quantification, and revealed fundamental differences between nano- and microscale systems that need to be considered in drawing conclusions about microscale objects from nanoscale models.24 Within the realm of 2D nanomaterials and investigations of how to control their properties, Prof. Karen Martinez and her co-workers at the University of Copenhagen in Denmark mapped the light distribution as well as the emitted fluorescence from vertical InAs nanowire antennas modified with fluorophore-conjugated proteins. They revealed the effect of nanowire orientation and excitation wavelength on fluorescence signals, providing an important understanding that will be useful for quantitative studies of biological phenomena measured on nanowires.25 Prof. Cherie Kagan and co-workers at the University of Pennsylvania used polymeric and oxide materials deposited onto p- or n-doped nanowires to control the dielectric environment surrounding these nanowires. They discovered that the doping efficiency of the nanowires is strongly influenced by the permittivity ε of the environment and concluded that controlling the environment’s ε should enhance doping concentrations in low-dimensional materials.26

of the cocatalytic platform of the Pt-nanoporous Au bowls, to improve the catalytic performance of Pt in the methanol oxidation reaction.11 To visualize the energy-transfer dynamics between a twodimensional (2D) array of plasmonic Au bowtie nanocavities and dye molecules directly, Prof. Teri Odom at Northwestern University and her collaborators imaged the energy transfer dynamics of the system. They demonstrated how array periodicity can alter nanoscopic kinetics at the nanoscale and single-unit nanolasing emission in the far-field.12 Prof. Catherine Murphy and her co-workers at the University of Illinois at UrbanaChampaign used two weak reducing agents, ascorbic acid and hydroquinone, in a seedmediated growth process to generate large amounts of sizecontrolled mini-Au nanorods with widths below 10 nm. The nanorods displayed a tunable longitudinal surface plasmon resonance from about 600 to over 1300 nm and longitudinal extinction coefficients in the range 1.6 × 108 to 1.4 × 109 M−1 cm−1.13 Although complete ligand exchange is usually assumed when citrate-stabilized Au nanoparticles are treated with thiol capping ligands, Prof. Jennifer Shumaker-Parry’s group at the University of Utah showed that a co-adsorption model is more likely, as hydrogen bonding between citrate groups leads to the formation of a stable network. When aminoacetates are used instead of the citrate, these are completely displaced in favor of the thiols.14 Different strategies have been adopted by the following researchers to assess the properties of nanostructures and to control the self- or field-assisted assembly of nanomaterials. Prof. Jill Millstone’s research group at the University of Pittsburgh used a solid-state nuclear magnetic resonance (ssNMR)-based approach to quantify the charge carrier density of doped semiconductor nanoparticles. They used 77 Se ssNMR spectroscopy to measure charge carrier density in a variety of Cu2−xSe nanoparticles and correlated the outcomes with particle crystallinity and extinction features.15 Prof. Sharon Glotzer’s research team at the University of Michigan studied colloidal building blocks of Voronoi particles and characterized their assembly behaviors in terms of the particle symmetry as well as its crystal structure. They demonstrated that the particle assembly propensity can be modulated by modifying factors related to packing degeneracies such as particle shape and external field.16 Prof. Maria Santore’s research group at the University of Massachusetts Amherst engineered nanoscale channel surfaces effective in controlling the rolling velocity and travel distance of microparticles flowing inside the channel. The team also identified combinations of parameters that can be used to manipulate particle movements for sustained microparticle rolling and particle size sorting.17 By controlling the periodicity and alignment of block copolymer (BCP) nanodomains, Prof. Jong-in Hahm at Georgetown University and her collaborators accomplished nanoscale surface assembly and large-area patterning of fibrinogen (Fg) protein. These authors revealed that dominant Fg adsorption configuration and surface packing preference can be tuned by the physical and chemical attributes of the underlying BCP nanodomains.18 By using a DNA origami approach, Prof. Barbara Saccà and co-workers at University of Duisburg-Essen assembled a module containing two quasi-independent domains and four possible interfaces with specific recognition patterns, which led B

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states with fast switching times between the transmissive and reflective modes.33 Prof. Michelle Simmons and co-workers at the University of New South Wales described a low-gate-density pathway to a scalable 1D building block of atomic-precision, singlet−triplet qubits using a donor-based quadruple-quantum-dot (QD) device. The QD pairs, each independently controlled via one gate and one reservoir, were designed to host two singlet− triplet qubits.34 The research works highlighted above exemplify the important and continuously growing contributions of women scientists and engineers to “Nanoscience, Nanotechnology & Beyond” and yet represent only a small fraction of the many exciting studies carried out by women investigators. Such leading research endeavors are anticipated to expand and to continue in the future with growing impacts to make a leap ‘toward better materials through a better understanding of lowdimensional systems’.

Nanomaterials have been of special importance in disease diagnosis and therapy. Prof. Molly Stevens and her research group at Imperial College London isolated porous Pt core− shell nanocatalysts with high catalytic activity in the presence of human blood serum samples. These nanocatalysts were used in a paper-based lateral flow immunoassay and enabled the naked-eye detection of p24, an early and most conserved biomarker for HIV, and the accompanying acute-phase HIV in clinical human plasma samples under 20 min.27 To achieve targeted drug delivery in gynecological health care, Prof. Mariana Medina-Sánchez at IFW Dresden in Germany and her co-authors developed a sperm-driven micromotor. The micromotor with the sperm cell, which is preloaded with an anticancer drug, can be guided magnetically toward the cancerous target, where the sperm is released upon reaching the tumor walls. The sperm cells penetrate the cell walls and are able to deliver the drug through the sperm− cancer cell membrane fusion.28 Since its discovery, graphene and its derivatives have been the target of many investigations. Prof. Liv Hornekaer at Aarhus University and her collaborators discovered that when graphene on Ir(111) is exposed to vibrationally excited H2 molecules, the ensuing functionalization results in nanopatterned structures. Calculations show that Ir promotes H2 adsorption and dissociation. Although the first molecule must contain considerable excitation energy, the initial adsorption activates the surface and, in an avalanche effect, additional H2 molecules with lower vibrational energy adsorb and dissociate more easily.29 With molecular dynamics simulations, Prof. Teresa HeadGordon at Lawrence Berkeley National Laboratory and her coworkers studied the phase behavior of water confined between flexible and rigid graphene sheets. They found that in rigid systems, there are discontinuous transitions between an (n)layer and an (n+1)-layer state at particular values of in-plane density. Flexible systems, on the other hand, are able to accommodate (n)-layer and (n+1)-layer states coexisting in equilibrium at the same density.30 Carbon nanotubes, a one-dimensional (1D) nanosystem related to graphene nanotechnology have been steadily examined in many studies. With the goal of increasing the synthetic yield of single-walled carbon nanotubes (SWNTs) that are 1.0−1.5 nm in diameter, Prof. Yan Li at Peking University and her collaborators used water vapor to control the structure of intermetallic W6Co7 nanocrystals with a high percentage of (1 0 10) planes, which were used as templates for nanotube formation. They reported the growth of predominantly (14,4) SWNTs with purities of ∼99 and 98.6%, with and without water, respectively.31 Much work has also been devoted to developing novel nanodevices and nanofabrication techniques. Prof. Natalia Litchinitser and her group at the University of Buffalo were able to isolate a hyperbolic metamaterial enabling hyperlenses with a large demagnification rate of 3.75. This photolithographic system enabled printing of feature sizes of 80 nm using a 405 nm laser source. Flattening the inner surface of the hyperlens to increase the working area and integrating it into a stepper system should enable the implementation of the hyperlens for practical application in nanolithography.32 Prof. Eunkyoung Kim’s research team at Yonsei University in Korea produced a reversible, bistable electrochemical grating from a periodically patterned Ag nanostructure. The Ag electrochemical grating yielded three distinct optical switch

Ana de Bettencourt-Dias* University of Nevada, Reno

Jong-In Hahm

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Georgetown University

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ana de Bettencourt-Dias: 0000-0001-5162-2393 Jong-In Hahm: 0000-0003-4395-1669 Notes

Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.

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REFERENCES

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DOI: 10.1021/acsnano.8b05854 ACS Nano XXXX, XXX, XXX−XXX