The need to improve health outcomes in the developing world and to moderate healthcare costs in developed countries has resulted in an increased interest in sophisticated, inexpensive, and instrument-free point-of-care diagnostics using porous materials. One major segment of the paper-based diagnostics effort is focused on developing high-performance point-of-care tests using porous nitrocellulose membranes. This review provides a perspective on the nature, history, and future of nitrocellulose-based assays. Beginning as a protein blotting substrate, porous nitrocellulose membranes have grown to be the most commonly used lateral flow substrate and are the primary membranes used in two-dimensional paper networks for user-friendly multistep assays. In addition to the historical context, we examine assay development considerations, such as the physics of flow in porous media, reagent deposition and storage, and detection methods.

Nano-sizing and scaffolding have emerged in the past decade as important strategies to control the kinetics, reversibility, and equilibrium pressure for hydrogen storage in light metal hydride systems. Reducing the size of metal hydrides to the nanometer range allows fast kinetics for both hydrogen release and subsequent uptake. Reversibility of the hydrogen release is impressively facilitated by nanoconfining the materials in a carbon or metal–organic framework scaffold, in particular for reactions involving multiple solid phases, such as the decomposition of LiBH4, NaBH4, and NaAlH4. More complex is the impact of nanoconfinement on phase equilibria. It is clear that equilibrium pressures, and even decomposition pathways, are changed. However, further experimental and computational studies are essential to understand the exact origins of these effects and to unravel the role of particle size, physical confinement, and interfaces. Nevertheless, it has become clear that nanoconfinement is a strong tool to change physicochemical properties of metal hydrides, which might not only be of relevance for hydrogen storage, but also for other applications such as rechargeable batteries.

Superconducting qubits are electronic circuits comprising lithographically defined Josephson tunnel junctions, inductors, capacitors, and interconnects. When cooled to dilution refrigerator temperatures, these circuits behave as quantum mechanical “artificial atoms,” exhibiting quantized states of electronic charge, magnetic flux, or junction phase depending on the design parameters of the constituent circuit elements. Their potential for lithographic scalability, compatibility with microwave control, and operability at nanosecond time scales place superconducting qubits among the leading modalities being considered for quantum information science and technology applications. Over the past decade, the quantum coherence of superconducting qubits has increased more than five orders of magnitude, due primarily to improvements in their design, fabrication, and, importantly, their constituent materials and interfaces. In this article, we review superconducting qubits, articulate the important role of materials research in their development, and provide a prospectus for the future as these devices transition from scientific curiosity to the threshold of technical reality.

Research on organic thin-film transistors tends to focus on improvements in device performance, but very little is understood about the ultimate limits of these devices, the microscopic physical mechanisms responsible for their limitations, and, more generally, the intrinsic transport properties of organic semiconductors. These topics are now being investigated through the study of transport in organic transistors realized using molecular single crystals of unprecedented chemical purity and structural quality. These studies are elucidating detailed microscopic aspects of the physics of organic semiconductors and corresponding devices and have also led to unforeseen high values for carrier mobility in these materials. Here, we discuss developments in this area and present a brief outlook on future goals that have come into experimental reach.

Condensation is a phase change phenomenon often encountered in nature, as well as used in industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance. Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of superhydrophobic surfaces with even higher droplet mobility and, in some cases, coalescence-induced droplet jumping. Here, we provide a review of new insights gained to tailor superhydrophobic surfaces for enhanced condensation heat transfer considering the role of surface structure, nucleation density, droplet morphology, and droplet dynamics. Furthermore, we identify challenges and new opportunities to advance these surfaces for broad implementation in thermofluidic systems.

Mesoscale (nanometers to microns) magnetic particles are becoming increasingly important in biomedical applications both in vitro for cell and tissue-based research and in vivo for clinical imaging and therapy. These applications generally rely on the fact that, while the body is relatively transparent to magnetic fields, magnetic particles within the body, or in ex vivo biological samples, will couple strongly to applied external fields. By synthesizing bio-functionalized, biocompatible polymer/magnetic particle composites, this remote coupling provides a mechanism for the precisely targeted actuation of cell signaling pathways, delivery of genes, targeted transmission of thermal energy, generation of tissue matrix, and imaging (via magnetic resonance imaging), among others. This article explores a variety of biomedical applications of mesoscale magnetic particles, some of which are routinely used in the clinic and in biomedical laboratories, with others approaching the realm of science fiction.

We have investigated protic ionic liquids (PILs) as proton conductors for non-humidified intermediate-temperature fuel cells. PILs exhibit proton conductivity and activity in fuel cell electrode reactions, as seen in acidic aqueous solutions and acidic polymer membranes. The wide molecular designability of PILs enabled the finding of a promising candidate, diethylmethylammonium trifluoromethanesulfonate ([dema][ TfO]), which exhibits favorable bulk properties and electrochemical activity. Solid thin films containing [dema][ TfO] were fabricated using sulfonated polyimide as a matrix polymer. By using the composite membrane, non-humidifying fuel cell operation at 120°C succeeded. The fuel cell performance can be further improved by the optimization of the catalyst layer and with further research on PILs.

Light emitted by molecules embedded within metal nanoparticle clusters is strongly enhanced by interaction with surface plasmons. This allows, for example, the observation of Raman scattering from individual molecules. The symmetry of the metal cluster may affect the Raman-scattered light by generating new polarization states. This article reviews the use of symmetry theory to analyze the plasmonic normal modes of metal nanoparticle trimers. The lowest bright energy modes are degenerate for an equilateral triangle but split when the symmetry is broken. When a single molecule in the gap between two of the particles emits, it excites the plasmon modes, typically off-resonance, and the ensuing interference between the modes rotates the polarization of the emitted light. This so-called Raman optical activity can generate circularly polarized light at the Raman frequency. This curious phenomenon, which was demonstrated experimentally, may prove useful for future plasmonic devices.

Defects in solid-state systems are responsible for much of what we take for granted in modern society, with applications ranging from electronics and lasers, to metallic alloys with tailored properties, and the unique characteristics of gemstones. As we enter the age of quantum technology, solid-state defects are also having their say, with substantial research focused on using their properties for fundamental tests of quantum mechanics, storage of quantum information, and investigations of quantum decoherence. Two of the most exciting prospects of quantum technology are the creation of computers that take advantage of quantum rather than classical laws to outperform current devices, and the realization of highly sensitive magnetometers limited only by quantum uncertainty. In pursuit of these two goals, many proposals and proof-of-principle experiments have been performed in the solid-state, which required location of defects very close to the host crystal’s surface. This article reviews recent work on creation of nitrogen-vacancy centers near the diamond surface and experiments toward the realization of these goals.

Artificially layered superlattices of oxide materials have been intensely investigated for some time, but continue to reveal new potential as a route to advanced functional materials. As well as considering electrostatics and strain, a more complete picture of the interfaces in these systems also needs to incorporate the possibility of additional structural distortions, electronic redistributions, and complex polarization domain structures. Here we focus on superlattices composed of two perovskite oxide materials, where one is a ferroelectric, and discuss the important interactions between the component materials that determine the behavior of the new artificial material. We discuss interfaces both with and without electronic screening. The first class of interface contains technologically relevant ultrathin ferroelectric capacitors and the more recently studied ferroelectric-metal superlattices. In these systems, the influence of the ferroelectric polarization decreases rapidly with distance from the interface. By contrast, in systems where the materials adjacent to the ferroelectric layers are dielectrics, the polarization of the ferroelectric layer influences the properties of the adjacent layers over a much longer distance, setting the stage for fascinating competition between the properties of the combined materials.

Lighting consumes almost one-fifth of all electricity generated today. In principle, with more efficient light sources replacing incandescent lamps, this demand can be reduced at least twofold. A dramatic improvement in lighting efficiency is possible by replacing traditional incandescent bulbs with light-emitting diodes (LEDs) in which current is directly converted into photons via the process of electroluminescence. The focus of this article is on the emerging technology of LEDs that use solution-processed semiconductor quantum dots (QDs) as light emitters. QDs are nano-sized semiconductor particles whose emission color can be tuned by simply changing their dimensions. They feature near-unity emission quantum yields and narrow emission bands, which result in excellent color purity. Here, we review spectroscopic studies of QDs that address the problem of nonradiative carrier losses in QD-LEDs and approaches for its mitigation via the appropriate design of QD emitters. An important conclusion of our studies is that the realization of high-performance LEDs might require a new generation of QDs that in addition to being efficient single-exciton emitters would also show high emission efficiency in the multicarrier regime.

New instrumentation is being developed to better understand the in vivo properties of magnetic particles suspended in solution or lodged in tissue. We describe three novel methods with the necessary sensitivity to measure the microscopic magnetic properties of individual magnetic particles and complexes quantitatively. The first method is based on proton nuclear magnetic resonance of a magnetic particle suspended in water in a microcapillary probe; the second method uses high-resolution magnetic resonance imaging of water surrounding a magnetic particle; and the third method is based on AC susceptometry with a magnetic cantilever that combines magnetic particle imaging concepts with probe microscopy. We present the physical basis for the measurements, estimate sensitivity limits, and discuss future impacts on the development of magnetic particles for bioimaging and bioassays.

The atoms at the surfaces of materials represent the frontier separating the bulk from the surrounding medium. Over the last decades, scientists have intensely studied the structure and properties of surfaces with the goal of understanding and improving the electronic and chemical properties of materials. The surface–medium interaction determines wetting, friction, chemical, biological, and electronic properties. The activity of catalysts, phenomena occurring in water droplets and particles in the atmosphere, and the electronic properties of semiconductor devices are direct consequences of surface-environment interactions. While the need to pursue studies in the normal environment that surrounds a material has always been recognized, the techniques used in the past have only partially fulfilled this need, as most of them work best under high vacuum conditions. My research over the last 10 years has focused on discovering the structure of a surface and its dynamics in real life—in everyday environments. This required the development of new techniques and methods. I present some of the new tools developed in my laboratory and new properties that were discovered by their application in the areas of environmental science, surface chemistry, and catalysis.

The aim of this article is to briefly review the progress made over the past few years in the theoretical description of the intrinsic charge-transport properties of organic molecular crystals. We first discuss the state-of-the-art methodologies used in the derivation of the electronic coupling and electron-phonon coupling constants. We illustrate the application of these techniques to two classes of semiconductors of interest for crystal-based organic electronics: crystals consisting of a single molecular building block, such as oligoacenes and their derivatives, and bimolecular crystals consisting of donor and acceptor compounds. After a brief overview of recent developments in the polaron modeling of the electronic and electrical properties of these systems, we examine the impact that the interplay between electronic interactions and various electron-phonon mechanisms has on the temperature dependence of the charge-carrier mobility.

Colloidal quantum dots (QDs) hold great promise as electrically excited emitters in light-emitting diodes (LEDs) for solid-state lighting and display applications, as highlighted recently by the demonstration of a red-emitting QD-LED with efficiency on par with that of commercialized organic LED technologies. In the past five years, important advances have been made in the synthesis of QD materials, the understanding of QD physics, and the integration of QDs into solid-state devices. Insights from this progress can be leveraged to develop a set of guidelines to direct QD-LED innovation. This article reviews the fundamental causes of inefficiency in QD-LEDs understood to date and proposes potential solutions. In particular, we emphasize the challenge in developing QD emitters that exhibit high luminescent quantum yields in the combined presence of charge carriers and electric fields that appear during traditional LED operation. To address this challenge, we suggest possible QD chemistries and active layer designs as well as novel device architectures and modes of QD-LED operation. These recommendations serve as examples of the type of innovations needed to drive development and commercialization of high-performance QD-LEDs.

Trapped ions are sensitive to electric-field noise from trap-electrode surfaces. This noise has been an obstacle to progress in trapped-ion quantum information processing (QIP) experiments for more than a decade. It causes motional heating of the ions, and thus quantum-state decoherence. This heating is anomalous because it is not easily explained by typical technical-noise sources. Experimental evidence of its dependence on ion-electrode distance, frequency, and electrode temperature points to the surface, rather than the bulk, of the trap electrodes as the origin. In this article, we review experimental efforts and models to help identify and reduce or eliminate the source of the anomalous heating. Recent progress to reduce the heating with in situ cleaning indicates that it may not be a fundamental limit to trapped-ion QIP. Moreover, the extreme sensitivity of trapped ions to electric-field noise may potentially be used as a new tool in surface science.

Bioactive paper, or paper that exhibits biorecognition properties, is a promising tool for on-site environmental monitoring. A critical parameter for production of paper-based sensors is the immobilization of biomolecules onto paper with retention of long-term activity. High loading, control over biomolecule orientation and accessibility, and protection of biomolecules from external denaturation need to be provided by the immobilization technique. We present here a summary of the current strategies for enzyme, antibody, bacteriophage, and aptamer immobilization on cellulose and provide examples of the application of bioactive paper in environmental monitoring.

Surface wettability has emerged as a powerful tool to influence phase change phenomena such as ice formation and steam condensation. Ice mitigation using passive coatings offers tremendous promise; however, there remain several fundamental, durability- and manufacturing-related challenges that need to be addressed to harness the benefits of these coatings. Challenges limiting industrial utilization of such coatings can be classified into three categories: fundamental (frost buildup, non-zero ice adhesion, bulk ice nucleation, variable icing conditions), durability-related (harsh environment resistance, liquid impact resistance, erosion, fatigue), and manufacturing-related (scalability, coating economics). The role of passive surfaces in enhancing condensation heat transfer is a potential game changer in power plant efficiency enhancement; however, the benefits of such coatings will only be realized when durability and manufacturing challenges have been fully addressed.