Functional magnetic nanoshells integrated nanosensor for trace analysis of environmental uranium contamination

Transuranic radionuclides such as uranium tend to be a pervasive environmental contaminant. It is absorbed through the intestine or a lung, deposited in the tissues, predominantly kidney and bone, and is carcinogenic. A novel nanosensor system has been developed for voltammetric tracing of environmental uranium contamination.The sensor consists of an organophosphorous ligand, (t-butylphenyl)-N,N-di-(isobutyl) carbamoylmethylphosphineoxide (CMPO) functionalized superparamagnetic core-shell magnetic nanoparticles and magnet based electrodes. It exploits the natural affinity of uranium for phosphate molecules to fabricate a highly specific and reproducible sensor. The small dimension along with a dramatically increased contact surface has lead to a faster response and higher sensitivity. The system uses an external magnetic field gradient for preconcentration and removal of the analyte from the surrounding aqueous media. The redox properties of the analyte are exploited for enumeration of variables by electrochemical techniques such as square wave voltammetry. The detection limit of the system is observed to be in parts-per-billion (ppb) of the uranyl concentration.     

The rise of inorganic nanomaterial implementation in food applications

The amalgamation of nanoparticles (NPs) with food industry has improved the quality of our lives despite the discovery of some plausible health concerns arising from the inclusion of NPs. Certain physical properties such as fine particle size, high surface area, and high reactivity are the preeminent reasons for the frequent application of NPs in a diversified range of industrial applications. The contribution of inorganic nanomaterials (INMs) is of great significance considering its potential for development of the food industry. Therefore, the toxicological impact on human health causes by INM-associated food applications is an issue currently being addressed. Albeit there being plenteous associations with nanomaterials in the food industry, inclusion of INMs is chiefly found in food packaging. INMs are also used to encapsulate sustenance supplements, develop sensors, or detectors that are utilizable in food applications and to boost the growth of crops. Only a limited number of elements such as Zn, Al, Ti, Au, Ag, Si, Cu, Co, and Fe and/or their derivatives have been documented as possible INMs befitting food applications. Implementation of most INMs is still in the research and development stage, and applications in the food industry are yet to find approval owing to health concerns. In this review recent findings, benefits, detriments, conveniences, and risks that are associated with INMs in food applications are discussed.     

Stochastic surface effects in nanobeam sensors

This work analyzes the statistical properties of nanobeam deflections due to stochastic surface stresses, induced by the surface adsorption/desorption of surrounding particles. A mechanical model for a heterogeneous nanobeam is first introduced. The model considers combined axial forces and bending moments due to non-uniform surface effects. Then, local surface interactions are statistically derived from the Langmuir interaction model and their corresponding stochastic surface stresses are introduced. Two types of nanobeam sensor are studied: a cantilever beam with pure surface bending effect and a clamped beam with mixed surface force and bending moment effects. The advantages of each type are discussed. The deflection statistics are found analytically and validated by Monte Carlo simulations. An analytical relation between the adsorption/desorption rates and the maximum deflection variance is found.     

Physical and Electrical Performance of Vapor–Solid Grown ZnO Straight Nanowires

Physical and electrical properties of wurtzitic ZnO straight nanowires grown via a vapor–solid mechanism were investigated. Raman spectrum shows four first-order phonon frequencies and a second-order Raman frequency of the ZnO nanowires. Electrical and photoconductive performance of individual ZnO straight nanowire devices was studied. The results indicate that the nanowires reported here are n-type semi-conductors and UV light sensitive, and a desirable candidate for fabricating UV light nanosensors and other applications.     

DNA nanotechnology: a future perspective

In addition to its genetic function, DNA is one of the most distinct and smart self-assembling nanomaterials. DNA nanotechnology exploits the predictable self-assembly of DNA oligonucleotides to design and assemble innovative and highly discrete nanostructures. Highly ordered DNA motifs are capable of providing an ultra-fine framework for the next generation of nanofabrications. The majority of these applications are based upon the complementarity of DNA base pairing: adenine with thymine, and guanine with cytosine. DNA provides an intelligent route for the creation of nanoarchitectures with programmable and predictable patterns. DNA strands twist along one helix for a number of bases before switching to the other helix by passing through a crossover junction. The association of two crossovers keeps the helices parallel and holds them tightly together, allowing the assembly of bigger structures. Because of the DNA molecule''s unique and novel characteristics, it can easily be applied in a vast variety of multidisciplinary research areas like biomedicine, computer science, nano/optoelectronics, and bionanotechnology.     

Mechanical strain modulation of domain wall currents across LiNbO3 nanosensors

Recently, studies on low-dimensional conducting domain walls (DWs) in insulating ferroelectrics have opened up new research areas that allow information to be mechanically written and electrically read on the nanoscale. Large strains in thin films can change the polarization gradient across the DW region and thus increasing the DW current significantly. This phenomenon can enable the development of high sensitivity mechanical vibration sensors. In this study, the effects of variable uniaxial strain on the structures of 180° conducting DWs in LiNbO₃ (LNO) single-crystal thin films bonded onto Si/SiO₂ substrates were investigated. After the creation of antiparallel domains within each LNO nanosensor integrated at the film surface, strain modulation of DW currents was observed through simple mechanical bending of the film. The DW current increases under application of tensile strain along the axis of polarization, but decreases under application of in-plane compression by a factor of approximately 25. Phase field simulations showed the dramatic change in polarization gradients around the DW regions under the increase in tensile strain, which reduced the band gap. Repetitive band-gap narrowing/broadening with change in local electric field intensity under vibrating mechanical forces can periodically modulate both the carrier density and the DW conduction in the sensors. This finding not only provides the new fundamental physics to enrich the ferroelectric theory, but also paves the way to the near-future development of bending actuators, piezolighters, and micro-/nano-manipulators, etc.     

Energy and spectrum-aware MAC protocol for perpetual wireless nanosensor networks in the Terahertz Band

Wireless NanoSensor Networks (WNSNs), i.e., networks of nanoscale devices with unprecedented sensing capabilities, are the enabling technology of long-awaited applications such as advanced health monitoring systems or surveillance networks for chemical and biological attack prevention. The peculiarities of the Terahertz Band, which is the envisioned frequency band for communication among nano-devices, and the extreme energy limitations of nanosensors, which require the use of nanoscale energy harvesting systems, introduce major challenges in the design of MAC protocols for WNSNs. This paper aims to design energy and spectrum-aware MAC protocols for WNSNs with the objective to achieve fair, throughput and lifetime optimal channel access by jointly optimizing the energy harvesting and consumption processes in nanosensors. Towards this end, the critical packet transmission ratio (CTR) is derived, which is the maximum allowable ratio between the transmission time and the energy harvesting time, below which a nanosensor can harvest more energy than the consumed one, thus achieving perpetual data transmission. Based on the CTR, first, a novel symbol-compression scheduling algorithm, built on a recently proposed pulse-based physical layer technique, is introduced. The symbol-compression solution utilizes the unique elasticity of the inter-symbol spacing of the pulse-based physical layer to allow a large number of nanosensors to transmit their packets in parallel without inducing collisions. In addition, a packet-level timeline scheduling algorithm, built on a theoretical bandwidth-adaptive capacity-optimal physical layer, is proposed with an objective to achieve balanced single-user throughput with infinite network lifetime. The simulation results show that the proposed simple scheduling algorithms can enable nanosensors to transmit with extremely high speed perpetually without replacing the batteries.     

Tin oxide nanosensors for highly sensitive toxic gas detection and their 3D system integration

We present nanosensors based on ultrathin SnO₂ films, which are very sensitive to the highly toxic gases SO₂ and H₂S. The SnO₂-sensing films are fabricated by a spray pyrolysis process on Si substrates with a thickness of 50 nm. The sensor resistance is decreased in the presence of the toxic gases. Exposure to 50 ppm SO₂ leads to a sensor resistance drop of ∼40% whereas a H₂S gas concentration of only 2.5 ppm decreases the resistance by ∼85%, which demonstrates the extraordinary sensitivity of the nanosensors. With respect to further system integration a CMOS technology based micro-hotplate containing heating element and sensing layer has been simulated. Preliminary results show that the micro-hotplates can provide operating temperatures of 400 °C with a power consumption of less than 5 mW. A concept for 3D system integration of the nanosensor chip and a CMOS chip based on Through-Silicon-Via (TSV) technology is proposed as potential roadmap towards smart nanosensor systems for daily life applications.