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We have demonstrated the detection of 2.5 μM target DNA labeled with 16 nm Fe3O4 nanoparticles (NPs) and 50 nm commercial MACS™ NPs using arrays of magnetic tunnel junction sensors with (001)-oriented MgO barrier layers. Signal-to-noise ratios of 25 and 12 were obtained with Fe3O4 and MACS™ NPs, respectively. These data show conclusively that MgO-based MTJ sensor arrays are very promising candidates for future applications involving the accurate detection and identification of biomolecules tagged with magnetic nanoparticles. [ABSTRACT FROM AUTHOR]

We report a facile method for assembly of a monolayer array of nitrogen-doped graphene (NG) and nanoparticles (NPs) and the subsequent transfer of two layers onto a solid substrate (S). Using 3 nm NiPd NPs as an example, we demonstrate that NiPd-NG-Si (Si=silicon wafer) can function as a catalyst and show maximum NiPd catalysis for the hydrolysis of ammonia borane (H3NBH3, AB) with a turnover frequency (TOF) of 4896.8 h−1 and an activation energy ( Ea) of 18.8 kJ mol−1. The NiPd-NG-S catalyst is also highly active for catalyzing the transfer hydrogenation from AB to nitro compounds, leading to the green synthesis of quinazolines in water. Our assembly method can be extended to other graphene and NP catalyst materials, providing a new 2D NP catalyst platform for catalyzing multiple reactions in one pot with maximum efficiency. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies have been carried out on the spin valve sensor signal dependence on the spatial locations of magnetic nanoparticles as potential biomolecular labels in the magnetic biodetection technology. Superparamagnetic 16 nm magnetite (Fe3O4) nanoparticles were site specifically deposited at different positions relative to a submicron-wide spin valve sensor. The spin valve sensor signal showed both polarity and magnitude differences with the particles at different positions. A theoretical model including magnetic sensor-particle interaction confirms the experimental results and provides a design guide to the sensing area. Moreover, the theoretical calculations reveal a nonmonotonic signal dependence on the vertical particle-to-sensor distance due to the sensor-particle interaction, and show that an optimum distance exists for signal strength and quantification. [ABSTRACT FROM AUTHOR]

We have fabricated a series of highly sensitive spin valve sensors on a micron scale that successfully detected the presence of a single superparamagnetic bead (Dynabeads M-280, 2.8 μm in diameter), and thus showed suitability for identifying biomolecules labeled by such magnetic beads. By polarizing the magnetic microbead on a spin valve sensor with a dc magnetic field and modulating its magnetization with an orthogonal ac magnetic field, we observed a magnetoresistance (MR) signal reduction caused by the magnetic dipole field from the bead that partially cancelled the applied fields to the spin valve. A lock-in technique was used to measure a voltage signal due to the MR reduction. A signal of 1.2 mV rms or 5.2 mΩ of resistance reduction was obtained from a 3 μm wide sensor and a signal of 3.8 mV rms or 11.9 mΩ from a 2.5 μm wide sensor. Micromagnetic simulations were also performed for the spin valve sensors with a single bead and gave results consistent with experiments. Further experiments and simulations suggested that these sensors or their variations can detect 1-10 Co nanoparticles with a diameter of ∼11 nm, and are suitable for DNA fragment detection. [ABSTRACT FROM AUTHOR]

Monodisperse FePt nanoparticles were prepared using high-temperature solution phase synthesis. Polymer-mediated layer-by-layer growth leads to precise control of the particle self assembly. The narrow particle size distribution (σ &les; 5%) offers the potential for increased data storage density by utilizing a smaller mean particle size and ultimately storage of one bit per individual nanoparticle. We have studied self-assembled multilayers of magnetic FePt nanoparticles. The L1[SUB0] phase of FePt has a very high magnetic anisotropy that allows the magnetization of particles of about 4 nm diameter to be thermally stable at room temperature. Magnetic measurements using a vibrating sample magnetometer were combined with x-ray diffraction (XRD) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy to study the annealed FePt nanoparticle assemblies and to optimize annealing conditions. NEXAFS spectra showed that a fraction of the iron in the as-deposited particles was oxidized, and this fraction was reduced by annealing in inert or reducing atmospheres. A very thin layer (<0.4 nm) of oxide surrounding the particle is sufficient to explain the observed spectra. Structural analysis using XRD showed that a minimum temperature of 450°C was required to start the formation of the ordered ferromagnetic phase. Annealing for longer times and at higher temperatures led to higher coercivity and a larger fraction of ordered phase but also to the onset of some agglomeration of the nanoparticles. [ABSTRACT FROM AUTHOR]

The shape-controlled synthesis of MnFe2O4 nanoparticles and shape-induced texture of the particles in a self-assembled superlattice is reported. Shape-induced texture of MnFe2O4 nanoparticles offers a practical example that chemical process can be used to regulate the growth of a particle and control the crystal orientation of a particle in a superlattice assembly.

Flexible pressure sensors have recently attracted increasing attention. Piezoresistive sensors are widely used in wearable devices, human health monitoring, electronic skin, human-computer interactions, and other fields owing to their good sensitivity and rapid response. The assembly of a pressure sensor using SnO 2 –ZnO hybrid nanofibers is proposed in this study to improve its performance. The heterojunction at the interface between ZnO and SnO 2 facilitates electron transfer from SnO 2 to ZnO by suppressing electron-hole recombination and accelerating electron motion in ZnO. The scaffold sensor, as compared to other reported pressure sensors, exhibits better flexibility, optimized sensitivity, and pressure sensing range, and can detect dynamic pressure over a wide range (0–60 kPa). The sensor exhibits strong sensitivity (11.5 kPa−1), fast response and recovery times of 42 and 28 ms, respectively, and durable cyclic stability (600 cycles). This sensor can quickly detect human motion from subtle deformations, including weak changes in the joints of the fingers, wrists, and elbows, with a bending degree of approximately 20°. Owing to its excellent performance, breathability, and washability, it can be directly attached to skin or clothing for long-term use and has broad application prospects in wearable electronics. [ABSTRACT FROM AUTHOR]

A simple chemical process of assembling FePt nanoparticles with control on assembly thickness and dimension is described. The process can be applied to any sized and shaped substrate thus offering a great potential for FePt-based nanodevice fabrication.

The sharing economy is a recent worldwide development; however, its impact on sustainability remains unclear, particularly in regards to the advancement of cleaner production. In order to explore the potential and contribution of specific sharing economy business practices in the transition to cleaner production, this study empirically analyzed how China's free-floating bike-sharing (FFBS) improved environmental sustainability through optimization of product life cycle design. Specifically, the impact on climate change and human health of three generations of shared bike products was quantitatively analyzed by using product environmental footprint (PEF) approach. The results show that sustainable product lifecycle design can effectively improve the sustainability of FFBS. Through optimized design and product upgrades, the environmental impact intensity of FFBS has decreased by approximately 25.09% –34.34%. This causes FFBS to gradually evolve from exerting negative impacts on climate change to achieving considerable climate benefits (22.18 CO 2 -eq/pkm). The environmental benefits on ozone depletion and photochemical ozone formation also increased by about 2.46 μg CFC11eq/pkm and 85.77 mg NMVOC eq/pkm with the upgrade of shared bikes from the first generation to the third generation. In addition, although the negative effects of FFBS on respiratory inorganics, non-cancer human health effects and cancer human health effects have been significantly reduced, the corresponding positive environmental benefits still need to be achieved by significantly increasing the utilization rate of shared bikes. Furthermore, this suggests that the sustainable production life cycle design of FFBS can follow the principles of safety, ease of maintenance, durability, ease of use, universality, resource conservation, and recyclability. This empirical study can not only help authorities, managers and the public better understand the contribution of the sharing economy to cleaner production, but also provides new insights and valuable references for improving the sustainability of the sharing economy. • The potential contribution of the sharing economy to cleaner production is explored. • The impact of product updates on the sustainability of free-floating bike-sharing (FFBS) is quantitatively estimated. • Sustainable product life cycle design can significantly improve the sustainability of FFBS. • The first-generation shared bike had a negative impact on the environment. • FFBS trips based on third-generation shared bikes can achieve considerable climate benefits. [ABSTRACT FROM AUTHOR]