A simple and direct biomolecule detection scheme based on a microwave resonator

Although several successful biosensors exist, they often require complex fabrication sequence or time-consuming sensing processes such as an off-site verification of a sensing result. At the same time, the biosensors generally focus on high sensitivity. This paper reports a cost-competitive biosensor that is capable of simple and direct detection of biomolecules without any off-site verification. The biosensor is realized with a microwave passive with a simple structure, a coplanar waveguide (CPW)-to-slotline ring resonator (CSRR) that resonant frequency is 3.375 GHz. The CSRR biosensor was then modified for higher sensitivity by increasing the effective sensing area. Two kinds of the CSRR biosensor were realized using micromachining technology. After simple fabrication, the biosensors were electrically characterized by measuring the resonant frequency shift as the biotin and streptavidin attached on the CSRR biosensor. The biotin and streptavidin induce a resonant frequency decrease of 65 and 10 MHz for the original CSRR biosensor, and 79 and 18 MHz for the modified CSRR biosensor, respectively. Based on the measurement of the resonant frequency shift, the relative permittivity of the biomolecules was calculated by numerical simulation, and was found to be 9800 for biotin and 500 for streptavidin.     

Development and optimization of the laser-assisted bonding process for a flip chip package

In a fine pitch flip chip package, a laser-assisted bonding (LAB) technology has recently been developed to overcome several reliability and throughput issues in the conventional mass reflow (MR) and thermal compression bonding technology. This study investigated the LAB process for a flip chip package with a copper (Cu) pillar bump using numerical heat transfer and thermo-mechanical analysis. During the LAB process, the temperature of the silicon die was uniform across the entire surface and increased to 280 °C within a few seconds; this was high enough to melt the solder. The heat in the die was quickly conducted to the substrate through the Cu pillar bumps. Meanwhile, the substrate temperature was low and remained constant. Therefore, a stable solder interconnection was quickly achieved with minimal stress and thermal damage to the package. The substrate thickness, the number of Cu bumps, and the bonding stage temperature were found to be important factors affecting the heat transfer behavior of the package. The temperature of the die decreased when a thinner substrate, a higher number of Cu bumps, and a lower bonding stage temperature were used. If the temperature of the die was not sufficiently high, insufficient heat was transferred to the solder to melt it, resulting in incomplete solder joint formation. Thermo-mechanical analysis also showed that the LAB process produced lower warpage and thermo-mechanical strain than the conventional MR process. These results indicated that a LAB process using a selective local heating method would be beneficial in reducing thermo-mechanical stress and increasing throughput for the fine pitch flip chip packages.

     

Carbon nanotube‐based thermoplastic polyurethane‐poly(methyl methacrylate) nanocomposites for pressure sensing applications

We have synthesized unique flexible pressure‐sensitive nanocomposites by means of a solution mixing method, by adding multiwalled carbon nanotubes (MWCNTs) into a thermoplastic urethane (TPU) matrix along with poly(methyl methacrylate) (PMMA) microbeads of various sizes. The influence of the various PMMA bead sizes on the pressure sensing properties of the nanocomposites was studied over a range of pressures. The PMMA microbeads were used to achieve an early percolation threshold at low loadings of MWCNTs. We used scanning electron microscopy to study the nanocomposites' morphology, and conducted differential scanning calorimetry analyses to investigate their thermal properties. The nanocomposites' electrical and thermal conductivities were also measured under various applied pressures. The nanocomposites displayed repeatable electrical responses under various applied pressures, demonstrating their suitability for use as pressure sensing materials. The proposed material is an ideal candidate for use in the preparation of pressure‐sensitive devices. POLYM. ENG. SCI. 56:1031–1036, 2016. © 2016 Society of Plastics Engineers     

An integrated sensor for pressure, temperature, and relative humidity based on MEMS technology

This paper presents an integrated multifunctional sensor based on MEMS technology, which can be used or embedded in mobile devices for environmental monitoring. An absolute pressure sensor, a temperature sensor and a humidity sensor are integrated in one silicon chip of which the size is 5 mmX 5 mm. The pressure sensor uses a bulk-micromachined diaphragm structure with the piezoresistors. For temperature sensing, a silicon temperature sensor based on the spreading-resistance principle is designed and fabricated. The humidity sensor is a capacitive humidity sensor which has the polyimide film and interdigitated capacitance electrodes. The different piezoresistive orientation is used for the pressure and temperature sensor to avoid the interference between sensors. Each sensor shows good sensor characteristics except for the humidity sensor. However, the linearity and hysteresis of the humidity sensor can be improved by selecting the proper polymer materials and structures.     

Secondary Sensitivity Control of Silver‐Nanowire‐Based Resistive‐Type Strain Sensors by Geometric Modulation of the Elastomer Substrate

A secondary method for modulation of the sensitivity in silver nanowire (AgNW) resistive‐type strain sensors without the need to change the material or coating process in the sensory layer is demonstrated. Instead of using a planar elastomer (polydimethylsiloxane is used in this study) substrate, diverse relief structures are introduced to induce nonuniform and complex strain within the elastic substrate and thereby different distributions of the crack density of the AgNWs upon stretching, which plays an important role in the modulation of the gauge factor (GF). Analysis of the sensory layer and mechanical studies reveal that a lower height ratio and greater number of trenches enhance the sensor sensitivity, for example, reaching a GF of 926 at 9.6% in this study. The demonstration of wrist‐motion sensors using the technology illustrates the feasibility of using relief structures for various types of sensors and sensitivity ranges using an identical sensor layer.     

Transformation of metal nanowires into metal nanotubes by a sequential thermal process

The simple, low-cost and scalable transformation of metallic nanowires to metallic nanotubes was demonstrated by employing sequential thermal treatments.

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Radical scavenging capacities of saba-narezushi,Japanese fermented chub mackerel,and its lactic acid bacteria

Narezushi (salted and fermented fish with rice) is a traditional Japanese food prepared using lactic acid-fermentation. In the current study, the antioxidant (2,2-diphenyl-1-picrylhydrazyl (DPPH^?)) and superoxide anion radical (O₂^?) scavenging capacities of four saba-narezushi (fermented chub mackerel with rice) products were determined. Lactose utilizing, bile resistant, acidophilic and antioxidative lactic acid bacteria (LAB) were also screened from 182 isolates derived from narezushi samples for use as starters of fermented foods as well probiotics. Radical scavenging capacities varied by product, with viable cell counts ranging from 7.9 to 9.4 log CFU/g and lactic acid content ranging from 0.27 to 1.2 mmol/g. Of the LAB isolates examined, five (four Lactobacillus plantarum and one Leuconostoc mesenteroides) were identified that were able to ferment lactose, grow in MRS containing 3 g/L bile, grow in broth adjusted to pH 3.6, and scavenge DPPH^? and/or O₂^? radicals. Two strains, Lb. plantarum 7FM10 and Ln. mesenteroides 1RM3, were able to grow and ferment in soybean milk and vegetable juice. These LAB also exhibited synergistic effects in milk fermentation, where samples containing both LAB showed a significant increase in O₂^? radical scavenging capacity.     

Analysis of InP Regrowth on Deep-Etched Mesas and Structural Characterization for Buried-Heterostructure Quantum Cascade Lasers

We investigated the effect of deep-etched mesa sidewall profile and oxide overhang length on the regrowth structural characteristics for buried- heterostructure (BH) quantum cascade lasers (QCLs) grown by metalorganic chemical vapor deposition (MOCVD). The relationship between etched mesa sidewall geometry, oxide overhang length, oxide thickness, and growth uniformity was examined and is extensively discussed. In particular, anomalous growth in the vicinity of the oxide edge resulting from insufficient oxide overhang length was identified and studied. An ideal ratio of mesa height to oxide overhang length between 2.5 and 3.0 is proposed and experimentally justified to yield satisfactory planar regrowths without anomalous growth. Mesas in the [ 0 1[` 1] ] [ 0 1\overline{ 1} ] direction with smoothly etched entrant profile yield a higher degree of growth uniformity than mesas in the [011] direction with the re-entrant profile.     

Synthesis and characterization of polymer–nanoclay conductive nanocomposites

Polymer–clay nanocomposites based on poly(3,4‐ethylenedioxythiophene)/polystyrene sulfonate (PEDOT) : PSS and nanoclay montmorillonite were synthesized and characterized. The doping of PEDOT with polystyrene sulfonate made it water dispersible (PEDOT–PSS). Sodium dodecyl benzene sulfonate (SDBS) and ionic liquid were used to increase the interlayer spacing and the conductivity of the nanocomposites, respectively. The nanocomposite was characterized by various techniques, such as X‐ray diffraction (XRD), TEM, surface resistivity, and thermogravimetric measurement analysis. Interlayer spacing increased as a result of the addition of SDBS, and this was confirmed by the 2θ shift observed via XRD analysis. The surface morphology of the conductive coated clay was examined by TEM analysis. Good electrical surface conductivity, interlayer spacing, and polymer coating were observed for the material prepared using the surfactant and conductive ionic liquid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of growth temperature on the coaxial InxGa1 − xN/GaN nanowires grown by metalorganic chemical vapor deposition

We report on the growth of coaxial In_xGa_1 − xN/GaN nanowires (NWs) on Si(111) substrates by using pulsed flow metalorganic chemical vapor deposition. The coaxial In_xGa_1 − xN/GaN NWs were grown by a two step process in which the core (GaN) structure was grown at a higher temperature followed by the shell (In_xGa_1 − xN) structure at a lower temperature. Dense and well-oriented coaxial In_xGa_1 − xN/GaN NWs were grown with an average diameter and length of about 300 ± 50 nm and 1.5-2.0 μm, respectively. The coaxial In_xGa_1 − xN/GaN NW was confirmed by cathodoluminescence mapping and high-resolution transmission electron microscopy. It is proposed that the critical dissociation of precursors at an elevated growth temperature can lead to a clear formation of an outer-shell in coaxial In_xGa_1 − xN/GaN NWs.