Nanoscale materials are beginning to have an impact in the field of molecular diagnostics. In particular, gold nanoparticles surface-functionalized with DNA have garnered much recent interest. Due to the unusual optical and catalytic properties of gold nanoparticle labels, several distinct advantages for assay readout have been realized. This review focuses on the progress made in our group over the past seven years in the development of particle surface chemistry and ultrasensitive protein and nucleic acid assays based upon DNA-functionalized gold nanoparticles. For DNA targets, experiments demonstrate that assays based upon gold nanoparticle labels have enhanced target specificity and in certain cases the sensitivity of polymerase chain reaction (PCR), without the need for target amplification. For protein targets, similar experiments demonstrate that assays based upon gold nanoparticles are up to one million times more sensitive than conventional protein detection methods. Recent data using human samples demonstrate the utility of such assays.

This article is an edited transcript based on a presentation given by Rebecca M. Bergman (Medtronic Inc.) as part of Symposium X—Frontiers of Materials Research on November 30, 2004, at the Materials Research Society Fall Meeting in Boston. Materials innovations have been at the heart of many important advances in implantable medical devices. Miniaturization, improved durability and longevity, enhanced biocompatibility, and controlled delivery are several areas where materials innovations have been important in advancing medical products and therapies. The demands on materials used in the physiological environment are stringent and include requirements related to materials properties as well as safety, quality, and reliability. Looking ahead, materials will undoubtedly continue to be an enabling technology for future innovations in medicine, including novel therapies such as tissue engineering, cell therapy, and gene therapy.

The design of safe and efficient gene transfer vectors remains one of the key challenges in gene therapy. Despite their remarkable transfection efficiency, viral vectors suffer from known safety issues. Consequently, significant research activity has been undertaken to develop nonviral approaches to gene transfer during the last decade. Numerous academic and industrial research groups are investigating synthetic cationic vectors, such as cationic amphiphiles, with the objective of increasing the gene transfection activity. Within this area, the development of functional synthetic vectors that respond to local environmental effects have met with success. These synthetic vectors are based on mechanistic principles and represent a significant departure from earlier systems. Many of these systems for gene delivery in vitro and in vivo are discussed in this article.

Numerous human diseases are associated with conformational change and aggregation of proteins, including Alzheimer's, Parkinson's, prion diseases (such as mad cow disease), familial amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), Huntington's, and type II (mature onset) diabetes. In many cases, it has been demonstrated that conformational change and aggregation can occur outside living cells and complex biochemical networks. Hence, approaches from materials and physical science have enhanced our understanding of the role of protein aggregation in these diseases at the molecular and nanoscale levels. In this article, we will review what is known about these protein structures from the perspective of materials science, focusing on the details of emergent oligomeric and nanotube-like structures, their interactions with model lipid bilayers, how the structures relate to observed biological phenomena, and how protein aggregation and amyloid formation can be employed for the good in biology and materials science.

Arthur von Hippel, a pioneer in the emergence of modern materials science, had a great goal: “the molecular designing of materials and devices.” In this article, I describe how computational materials theory has evolved over the last half century, helping to transform that goal from dream to reality. I start with two great puzzles of the 1950s: why band theory and the nearly free electron picture work. These were resolved by Landau's quasiparticle theory and by pseudopotential theory, respectively.Together with the creation and development of density functional theory, key methodological advances, and the rapid evolution of computer hardware and software, these two insights have resulted in the achievement of the quantitative prediction of the structures and properties of complex materials. Bandgapengineering and design of multilayer multifunctional materials are given as examples of “molecular design.”

Recently, a variety of patterning techniques have reached feature sizes of 100 nm or less, a size range very relevant to biology. Proteins, vesicles, and macromolecular assemblies can now be handled and specifically placed onto predefined artificial patterns, triggering defined functions in cells and revealing the details of cell–surface interactions. Simultaneously, novel surface chemistries have been developed that are able to induce specific bioresponses (e.g., mimicking the features of the extracellular matrix) and at the same time suppress the nonspecific effects of complex biological solutions. This article reviews the basic principles and properties of multifunctional physisorbed monolayers that can be used in combination with nanopatterning techniques to create biologically relevant surface features. Furthermore, selected examples of nanopatterns created by novel combinations of different top-down and bottom-up approaches are presented, including systems with specific bioligands, proteins, vesicles, and cells.

Self-assembly—the spontaneous generation of order in systems of components—is ubiquitous in chemistry; in biology, it generates much of the functionality of the living cell. Self-assembly is relatively unused in microfabrication, although it offers opportunities to simplify processes, lower costs, develop new processes, use components too small to be manipulated robotically, integrate components made using incompatible technologies, and generate structures in three dimensions and on curved surfaces. The major limitations to the self-assembly of micrometer- to millimeter-sized components (mesoscale self-assembly) do not seem to be intrinsic, but rather operational: selfassembly can, in fact, be reliable and insensitive to small process variations, but fabricating the small, complex, functional components that future applications may require will necessitate the development of new methodologies. Proof-of-concept experiments in mesoscale self-assembly demonstrate that this technique poses fascinating scientific and technical challenges and offers the potential to provide access to hard-to-fabricate structures.

Fabrication of bulk heterojunctions with well-ordered arrays of organic and inorganic semiconductors is a promising route to increasing the efficiency of polymer photovoltaic cells. In such structures, almost all excitons formed are close enough to the organic–inorganic interface to be dissociated by electron transfer, all charge carriers have an uninterrupted pathway to the electrodes, and polymer chains are aligned to increase their charge carrier mobility. Furthermore, ordered structures are interesting because they are relatively easy to model. Studies of ordered cells are likely to lead to better design rules for making efficient photovoltaic cells.

The recent discovery of forward-voltage degradation in SiC pin diodes has created an obstacle to the successful commercialization of SiC bipolar power devices. Accordingly, it has attracted intense interest around the world. This article summarizes the progress in both the fundamental understanding of the problem and its elimination.The degradation is due to the formation of Shockley-type stacking faults in the drift layer, which occurs through glide of bounding partial dislocations. The faults gradually cover the diode area, impeding current flow. Since the minimization of stress in the device structure could not prevent this phenomenon, its driving force appears to be intrinsic to the material. Stable devices can be fabricated by eliminating the nucleation sites, namely, dissociated basal-plane dislocations in the drift layer.Their density can be reduced by the conversion of basal-plane dislocations propagating from the substrate into threading dislocations during homoepitaxy.

The controlled formation of submicrometer-scale structures in three dimensions is of increasing interest in many applications. Not intended to produce the smallest structures, but instead aimed at complex topographies, two-photon lithography is an intrinsic 3D lithography technique that enables the fabrication of structures difficult to access by conventional single-photon processes with far greater spatial resolution than other 3D microfabrication techniques. By tightly focusing a femtosecond laser beam into a resin, subsequent photo-induced reactions such as polymerization occur only in the close vicinity of the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns. The current research effort in two-photon lithography is largely devoted to the design and synthesis of high-efficiency photoinitiators and sensitizers, as well as the development of new materials and systems. This article provides an overview of the progress in two-photon processes for the formation of complex images and the development of patterned structures.

Recent results have demonstrated that hybrid photovoltaic cells based on a blend of inorganic nanocrystals and polymers possess significant potential for low-cost, scalable solar power conversion. Colloidal semiconductor nanocrystals, like polymers, are solution processable and chemically synthesized, but possess the advantageous properties of inorganic semiconductors such as a broad spectral absorption range and high carrier mobilities. Significant advances in hybrid solar cells have followed the development of elongated nanocrystal rods and branched nanocrystals, which enable more effective charge transport. The incorporation of these larger nanostructures into polymers has required optimization of blend morphology using solvent mixtures. Future advances will rely on new nanocrystals, such as cadmium telluride tetrapods, that have the potential to enhance light absorption and further improve charge transport. Gains can also be made by incorporating application-specific organic components, including electroactive surfactants which control the physical and electronic interactions between nanocrystals and polymer.

The following article is based on a presentation given by Samuel I. Stupp of Northwestern University as part of Symposium X—Frontiers of Materials Research on April 13, 2004, at the Materials Research Society Spring Meeting in San Francisco. Materials designed at the molecular and supramolecular scales to interact with cells, biomolecules, and pharmaceuticals will have a profound impact on technologies targeting the regeneration of body parts. Materials science is a great partner to stem cell biology, genomics, and proteomics in crafting the scaffolds that will effectively regenerate tissues lost to trauma, disease, or genetic defects. The repair of humans should be minimally invasive, and thus the best scaffolds would be liquids programmed to create materials inside our bodies. In this regard, self-assembling materials will play a key role in future technologies. This article illustrates how molecules are designed to assemble into cell scaffolds for human repair and provides examples relevant to brain damage, fractures of the skeleton, spinal cord injuries leading to paralysis, and diabetes.

The function of biologically important ion channels can be measured in supported lipid membranes by impedance spectroscopy. This approach offers substantial advantages over traditional electrophysiological measurements. In this article, we present an overview of the field, with a special emphasis on the reconstitution of ion channels in lipid bilayers tethered to gold electrodes and the modulation of their channel activity by specific ligand binding.

The transmission of light through a hole was thought to be very weak when all of the lateral dimensions of the hole were much smaller than the wavelength of the light.The discovery of enhanced transmission has changed this view, raising fundamental questions and leading to many practical applications ranging from photonics to chemical sensing. A key feature of the transmission process is the activation of surface plasmons. In this article, we review the present understanding of this phenomenon and illustrate its potential through several examples of applications in different fields.

Significant progress has been made in the development of SiC metal semiconductor field-effect transistors (MESFETs) and monolithic microwave integrated-circuit (MMIC) power amplifiers for high-frequency power applications. Three-inch-diameter high-purity semi-insulating 4H-SiC substrates have been used in this development, enabling high-volume fabrication with improved performance by minimizing surface- and substrate-related trapping issues previously observed in MESFETs. These devices exhibit excellent reliability characteristics, with mean time to failure in excess of 500 h at a junction temperature of 410°C. A sampling of these devices has also been running for over 5000 h in an rf high-temperature operating-life test, with negligible changes in performance. High-power SiC MMIC amplifiers have also been demonstrated with excellent yield and repeatability. These MMIC amplifiers show power performance characteristics not previously available with conventional GaAs technology. These developments have led to the commercial availability of SiC rf power MESFETs and to the release of a foundry process for MMIC fabrication.