It is not often that the prefix multipliers kilo and nano come together, and when they do, it usually is in the opening chapters of physical sciences textbooks where the point is made that the universe around us spans enormous space and time scales while operating in unimaginably small ones. We are truly awestruck and inspired by the tension. Kilometer-long nanowires do have a similar eponymous echo. Researchers have now reported the first successful fabrication of arrays of millions of ordered indefinitely long nanowires and nanotubes in a flexible polymer fiber. The results are kilometer-long nanowires - a novel approach to nanowire fabrication that might bring with it fresh solutions.
The future of your shirts, socks and gloves will be electronic. In years to come, wearable electronics will look nothing like even your smallest iPod or mobile phone today. Not only will such devices be embedded on textile substrates, but an electronics device or system could become the fabric itself. Here is some recent work that demonstrates the kind of issues scientists are working on today and that will help improve the performance of electronic textile structures. Using atomic layer deposition (ALD), researchers have grown coatings of inorganic materials on the surface of textiles like woven cotton and nonwoven polypropylene. By fabricating an all-fiber capacitor, they show that their coated materials are sufficiently conductive to perform in simple device architectures.
In a standard dye sensitized solar cell, an organic molecule adsorbed on the surface of a porous electrode absorbs light and then initiates the charge separation process eventually leading to generation of photocurrent. While the dye appears to have "sensitized" the large bandgap material, it never actually does, because only the dye molecules absorb the light and generate the carriers, the large bandgap material primarily serves the function of a conducting channel to take the electrons out. While wide bandgap materials alone can not absorb the sun light efficiently, it has been predicted that if two large bandgap materials with type-II band alignment form coaxial nanowires, the effective indirect bandgap could be substantially smaller than either of the individual materials. After a few years effort, one research team has now demonstrated a real functional device that exhibits the key feature of the idea: the use of two large bandgap materials to make a solar cell behaving like a small bandgap material.
In order to get a true picture of the processes and events that take place inside unmodified, living cells, probing techniques need to be non-destructive, noninvasive and in real-time. Due to their small dimensions, high-aspect ratio nanomaterials such as nanofibers, nanowires and carbon nanotubes are ideal for cellular applications since they can cross the cell membrane without causing significant damage. In particular, semiconductor nanowires attract a lot of interest because of their uniformity, reproducibility and possibility of fine-tuning their intrinsic properties - physical dimensions, crystal structure, electrical and optical properties, etc. Researchers have now shown, for the first time, the spontaneous and close interface of arrays of vertically aligned indium arsenide nanowires with two relevant cell lines, human embryonic kidney cells and rat embryonic dorsal root ganglion neurons.
Nanowires - particularly those of silicon - promise great potentials for high-efficiency, low-cost solar energy conversion. This promise has not yet been met by experimental evidence, raising fundamental questions whether silicon nanowires are intrinsically disadvantaged and whether the photovoltaic research community should continue working on this material. Despite intense efforts, the performance of silicon nanowire-based solar cells remains significantly lower than what has been achieved for bulk silicon or micrometer-scale wires. The gap between the predicted performance and the inability to deliver raises an important question with regard to the origin of this problem. New research shows that the poor performance is not a result of the nanowire morphology, but is intrinsic to the growth chemistry.
Nanotechnology-enabled fabrication of solar cells with conventional nanoparticle-based thin-films has a drawback in that the diffusion length of the charge carriers is too short to get charge separation, although the nanoparticles themselves provide copious surface areas; whereas photovoltaic devices fabricated by aligned or partially aligned nanowire array configurations have exhibited enhanced performance owing to improved carrier collection, reduced optical reflection, and efficient absorption. While the nanowire-based approach indeed increases the diffusion length of carriers it also reduces the available surface area. However, being able to fully capture the promising surface and transport properties of nanoscale materials in practical devices or systems relies on the capability of effectively translating the extraordinary characteristics of nanoparticles or nanowires into larger-scale, three-dimensional (3D) structures. Researchers now have come up with a promising approach to address this problem by growing uniformly distributed and high density nanorods into high-aspect ratio nanochannels.
Nanotechnology researchers working on self-powered nanodevices - nanoscale systems that scavenge energy from their surrounding environment - have been experimenting with various power sources ranging from piezoelectric systems to sound. However, the most abundant energy available in biosystems is chemical and biochemical energy, such as glucose. Researchers in China have now reported a nanowire-based biofuel cell based on a single proton conductive polymer nanowire for converting chemical energy from biofluids into electricity, using glucose oxidase and laccase as catalyst. The output of this biofuel cell is sufficient to drive pH, glucose or photon sensors. The high output power, low cost and easy fabrication process, large-scale manufacturability, high 'on-chip' integrability and stability demonstrates its great potential for in vivo biosensing.
Off-targeting remains a key challenge of researchers working on nanoparticle drug delivery - the majority of intravenously administered therapeutic nanoparticles are also reaching normal tissues, resulting in considerable adverse side effects. Another challenge of nanoparticle drug delivery includes the limited penetration depth of particles into the tumors. While extensive efforts have been devoted for designing therapeutic nanoparticles, a new study - echoing the journey through the human body in Fantastic Voyage - represents the first example of coupling such drug nanocarriers with self-propelled nanoshuttles. The ability of synthetic nanomotors to carry 'cargo' has already been demonstrated; but not in connection to common drug-loaded particles. In a new study, researchers demonstrate that catalytic nanoshuttles can readily pickup common biocompatible and biodegradable drug-loaded particles and liposomes and transport them over predefined routes towards predetermined destination.