Assembling Vertical Nanogap Arrays with Nanoentities for Highly Sensitive Electrical Biosensing.

Nanogap biosensors have emerged as promising platforms for detecting and measuring biochemical substances at low concentrations. Although the nanogap biosensors provide high sensitivity, low limit of detection (LOD), and enhanced signal strength, it requires arduous fabrication processes and costly equipment to obtain micro/nanoelectrodes with extremely narrow gaps in a controlled manner. In this work, we report the novel design and fabrication processes of vertical nanogap structures that can electrically detect and quantify low-concentration biochemical substances. Approximately 40 nm gaps are facilely created by magnetically assembling antibody-coated nanowires onto a nanodisk patterned between a pair of microelectrodes. Analyte molecules tagged with conductive nanoparticles are captured and bound to nanowires and bridge over the nanogaps, which consequently causes an abrupt change in the electrical conductivity between the microelectrodes. Using biotin and streptavidin as model antibodies and analytes, we demonstrated that our nanogap biosensors can effectively measure the protein analytes with the LOD of ∼18 pM. The outcome of this research could inspire the design and fabrication of nanogap devices and nanobiosensors, and it would have a broad impact on the development of microfluidics, biochips, and lab-on-a-chip architectures.

An angle-compensating colorimetric strain sensor with wide working range and its fabrication method.

The visual response is one of the most intuitive principles of sensors. Therefore, emission and change of the colors are widely studied for development of chemical, thermal and mechanical sensors. And it is still a challenging issue to fabricate them with a simple working mechanism, high sensitivity, good reliability, and a cost-effective fabrication process. In this study, we propose a mechanical strain sensor, which has 2D photonic crystal structures in nanoscale on stretchable polydimethylsiloxane (PDMS) substrate. Due to the periodic nanostructures, the surface of the sensor produces structural colors. And when it is stretched, the periodicity of the nanostructures changes, which results in the shift of the colors. Multiple nanostructures with different periodicities are integrated on the sensor in order to extend the working range up to 150% with high sensitivity. In addition, reusable and robust molds, which are fabricated by self-assembly of nanoparticles, are used for multiple replications of sensor substrates. Thus, the fabrication process of this study is believed to be potential for possible industrial manufacturing. This study is expected to contribute to strain sensors in the future for the applications of health care, infrastructure monitoring, soft robotics, and wearable devices.

Fabrication of robust and reusable mold with nanostructures and its application to anti-counterfeiting surfaces based on structural colors.

In this study, we report a method to fabricate molds and flexible stamps with 2D photonic crystal structures. This includes self-assembly of polystyrene particles into monolayer, oxygen reactive ion etching, thin film (chromium (Cr)) deposition, and polydimethylsiloxane replication. By tuning the thickness of Cr layer, reusable master molds with nano bumps or nano concaves could be prepared selectively. We showed that the replicated flexible stamps out of these molds exhibited structural colors. Characteristics of the colors depended on viewing angle, brightness of background and light source. And the colors even faded out when the background is white or when the stamp was bent. By using this feature, possible strategies for anti-counterfeiting applications have been suggested in this study. Since the molds are reusable and the fabrication method is simple and cost-effective, this study is expected to contribute to nano devices for industries in future.

Electrical, Structural, Optical, and Adhesive Characteristics of Aluminum-Doped Tin Oxide Thin Films for Transparent Flexible Thin-Film Transistor Applications.

The properties of Al-doped SnOx films deposited via reactive co-sputtering were examined in terms of their potential applications for the fabrication of transparent and flexible electronic devices. Al 2.2-atom %-doped SnOx thin-film transistors (TFTs) exhibit improved semiconductor characteristics compared to non-doped films, with a lower sub-threshold swing of ~0.68 Vdec-1, increased on/off current ratio of ~8 × 107, threshold voltage (Vth) near 0 V, and markedly reduced (by 81%) Vth instability in air, attributable to the decrease in oxygen vacancy defects induced by the strong oxidizing potential of Al. Al-doped SnOx films maintain amorphous crystallinity, an optical transmittance of ~97%, and an adhesive strength (to a plastic substrate) of over 0.7 kgf/mm; such films are thus promising semiconductor candidates for fabrication of transparent flexible TFTs.

Nano sand filter with functionalized nanoparticles embedded in anodic aluminum oxide templates.

Since the ancient Egyptians had used sand as filter media for water purification, its principle has been inherited through generations and it is still being used now in industries. The sand filter consists of sand literally, and the voids within the sand bed are the pores for filtration. Here we present a filtration principle using nanoparticles, so that the voids between the nanoparticles can be considered as effective pores in nanoscale dimension. Anodic aluminum oxide (AAO) membrane has been used as the working template, and the nanoparticles have been injected and embedded within the pores of the AAO template. Nanoparticles with multiple sizes have been used in order to obtain smaller voids. Moreover, the nanoparticles have been functionalized, or electrically charged, with arginine/phenylalanine (RF) peptide group. In this way, filtration performance for charged particles or molecules, such as methylene blue, has been enhanced. Consequently, this study is expected to provide a new principle for fabrication of nano voids, or nano pores, and for filtration in nanoscale dimension.

Effect of fermented earthworm cast on egg production and egg quality as well as removal of odor in feces from egg laying hens.

The objective of the present study was to determine the effect of feeding fermented earthworm casts (EEC) to layers on egg-laying performance, blood lipid profiles, cecal microflora, and fecal odor removing performance. A total of 200 Hyline Brown layer chicks at 33-week-old were used in this study. They were randomly assigned to two numerically equal groups with 100 replications per treatment for 10 weeks. All the birds were caged individually. The control group was not treated with EEC. The EEC group was treated with top dressing containing 3.5% EEC. The present study revealed that egg production and egg weight were increased after feeding diet containing EEC at the top dressing level. Haugh unit, eggshell thickness, and eggshell breaking strength of EEC group were higher than those of control group. Egg yolk was determined for fatty acid profiling. It was found that EEC group had higher ratio of unsaturated- to saturated fatty acid as compared to control group. Lower ratios of n-6 to n-3 fatty acids were found in the egg yolk of EEC group. Plasma triglyceride and total cholesterol contents were lower in the EEC group. However, high density lipoprotein-cholesterol content was higher in the EEC group as compared to that in control group. The number of cecal Lactobacillus was increased while the population of Escherichia coli and coliform bacteria decreased in the EEC group. Fecal ammonia and hydrogen sulfide contents were lower in the EEC group as compared to those in control group. Taken together, these results suggested that EEC could improve egg production and egg quality. In addition, it could remove odour from laying-hen manure.

Automated lipid membrane formation using a polydimethylsiloxane film for ion channel measurements.

A black lipid membrane (BLM) is a powerful platform for studying the electrophysiology of cell membranes as well as transmembrane proteins. However, BLMs have disadvantages in terms of stability, accessibility, and transportability, which preclude their industrial applications. To resolve these issues, frozen membrane precursor (MP) was devised to improve the transportability and storability of BLMs. As described previously, MP is a storable and transportable platform that can be delivered to the point-of-use, where BLMs are automatically formed upon thawing at room temperature. However, MP has an inconsistent thinning-out time, ranging from 30 min to 24 h, as well as a low success rate of BLM formation (~27%), which make it undesirable for practical use. In our study, polydimethylsiloxane (PDMS) was introduced as a replacement for conventionally used Teflon film to control thinning-out time. As such, we used a PDMS thin-film, a porous-structured hydrophobic polymer, and squalene, a high viscosity solvent, to facilitate membrane formation, whereas the absorption rates of solvents were controlled to achieve consistent BLM formation time. We successfully reduced thinning-out time down to <1 h as well as enhanced the success rate of BLM formation to greater than 80%. Moreover, we demonstrated the feasibility of our platform for use in drug screening using gramicidin A and guanidine.