Taechang An

Preparation of stable superhydrophobic mesh with a biomimetic hierarchical structure

Stable superhydrophobic meshes with a biomimetic hierarchical structure were fabricated via simple electropolymerization and chemical polymerization processes. Because the multi-scale hierarchical structure provides a stable superhydrophobic state by maintaining a Cassie state, these meshes have high static and dynamic waterproof capabilities.

Replicable Multilayered Nanofibrous Patterns on a Flexible Film

This report describes a simple method for the direct patterning of nanofibers on a flexible, insulating film. The method allows the replication of nanofibrous patterns from a single patterned electrode and the fabrication of multilayered patterns from various electrode shapes. The architecture of the fibrous patterns can be controlled by tailoring the ambient humidity, thickness of the insulating film, polarity of the electrode, and size of the patterned electrode. Using this novel technique, it is possible to fabricate various complex patterns of nanofibers as well as inexpensive patterned structures.

Fabrication of functional micro- and nanoneedle electrodes using a carbon nanotube template and electrodeposition

Carbon nanotube (CNT) is an attractive material for needle-like conducting electrodes because it has high electrical conductivity and mechanical strength. However, CNTs cannot provide the desired properties in certain applications. To obtain micro- and nanoneedles having the desired properties, it is necessary to fabricate functional needles using various other materials. In this study, functional micro- and nanoneedle electrodes were fabricated using a tungsten tip and an atomic force microscope probe with a CNT needle template and electrodeposition. To prepare the conductive needle templates, a single-wall nanotube nanoneedle was attached onto the conductive tip using dielectrophoresis and surface tension. Through electrodeposition, Au, Ni, and polypyrrole were each coated successfully onto CNT nanoneedle electrodes to obtain the desired properties.

Carbon-Nanotube-Modified Electrodes for Highly Efficient Acute Neural Recording

Microelectrodes are widely used for monitoring neural activities in various neurobiological studies. The size of the neural electrode is an important factor in determining the signal-to-noise ratio (SNR) of recorded neural signals and, thereby, the recording sensitivity. Here, it is demonstrated that commercial tungsten microelectrodes can be modified with carbon nanotubes (CNTs), resulting in a highly sensitive recording ability. The impedance with the respect to surface area of the CNT-modified electrodes (CNEs) is much less than that of tungsten microelectrodes because of their large electrochemical surface area (ESA). In addition, the noise level of neural signals recorded by CNEs is significantly less. Thus, the SNR is greater than that obtained using tungsten microelectrodes. Importantly, when applied in a mouse brain in vivo, the CNEs can detect action potentials five times more efficiently than tungsten microelectrodes. This technique provides a significant advance in the recording of neural signals, especially in brain regions with sparse neuronal densities.

Ionic liquid flow along the carbon nanotube with DC electric field

Liquid pumping can occur along the outer surface of an electrode under a DC electric field. For biological applications, a better understanding of the ionic solution pumping mechanism is required. Here, we fabricated CNT wire electrodes (CWEs) and tungsten wire electrodes (TWEs) of various diameters to assess an ionic solution pumping. A DC electric field created by a bias of several volts pumped the ionic solution in the direction of the negatively biased electrode. The resulting electro-osmotic flow was attributed to the movement of an electric double layer near the electrode, and the flow rates along the CWEs were on the order of picoliters per minute. According to electric field analysis, the z-directional electric field around the meniscus of the small electrode was more concentrated than that of the larger electrode. Thus, the pumping effect increased as the electrode diameter decreased. Interestingly in CWEs, the initiating voltage for liquid pumping did not change with increasing diameter, up to 20 μm. We classified into three pumping zones, according to the initiating voltage and faradaic reaction. Liquid pumping using the CWEs could provide a new method for biological studies with adoptable flow rates and a larger ‘Recommended pumping zone’.

Cell behaviour on a polyaniline nanoprotrusion structure surface

The extracellular matrix provides mechanical support and affects cell behaviour. Nanoscale structures have been shown to have functions similar to the extracellular matrix. In this study, we fabricated nanoprotrusion structures with polyaniline as cell culture plates using a simple method and determined the effects of these nanoprotrusion structures on cells.

Bioinspired Structural Colors Fabricated with ZnO Quasi-Ordered Nanostructures

Despite their advantages in different applications, structural colors are difficult to use because of the inability to change a structural color once it is implemented, as well as their high fabrication costs; implementing multiple structural colors simultaneously on one substrate is a challenge as well. In this study, structural colors were reproduced using quasi-ordered scattering to mitigate these issues. To this end, a ZnO flower-like structure having unimodal distributions of size and spacing was fabricated by ZnO hydrothermal growth. This fabricated nanostructure has a thickness on the order of 103 nm and a diameter on the order of 102 nm. The thickness and diameter increase in proportion with the synthesis time (thickness growth rate = 43 nm/min, diameter growth rate = 20 nm/min). The shape of the nanostructure can be easily tuned by simply adjusting the synthesis and etching times. This method combines the advantages of top-down and bottom-up synthetic approaches in that the structural color can be continuously modified once fabricated.

Fabrication and Calibration of pH Sensor Using Suspended CNT Nanosheet

In this research, the pH sensor was developed using CNT nanosheet with Nafion coating for the advanced medical sensor such as a blood gas analyzer. The CNT nanosheet was formed by dielectrophoresis and water-meniscus between cantilever-type electrodes. Then, the process of the heat annealing and the Nafion coating was conducted for reducing contact resistance and giving proton selectivity respectively. We measured the response of the pH sensor as the electrolyte-gated CNT-nanosheet field effect transistor. The sensor showed a linear current ratio in a similar range of the normal blood pH. A calibration method for decreasing of the response variation among sensors has also been introduced. Coefficient of variance of the pH sensor was decreased by applying the calibration method. A linear relation between the calibrated response of the sensors and pH variance was also obtained. Finally, the pH sensor with a high resolution was fabricated and we verify the feasibility of the sensor by applying the calibration method.

Site-specific immobilization of microbes using carbon nanotubes and dielectrophoretic force for microfluidic applications

We developed a microbial immobilization method for successful applications in microfluidic devices. Single-walled nanotubes and Escherichia coli were aligned between two cantilever electrodes by a positive dielectrophoretic force resulting in a film of single-walled nanotubes with attached Escherichia coli. Because this film has a suspended and porous structure, it has a larger reaction area and higher reactant transfer efficiency than film attached to the substrate surface. The cell density of film was easily controlled by varying the cell concentration of the suspension and varying the electric field. The film showed excellent stability of enzyme activity, as demonstrated by measuring continuous reaction and long-term storage times using recombinant Escherichia coli that expressed organophosphorus hydrolase.

Fabrication of Conducting Polymer Nanowires

The advancement of nanotechnology provides opportunities for fabrication of nanoscale materials and higher performance devices using nanomaterials with high precision. Currently, various nanomaterials and nanostructures in the range of 1 to 100 nm have been produced by chemical and physical methods. Among various nanostructured materials, one-dimensional (1D) materials, such as nanowires, nanotubes, nanorods, and nanobelts, have potential applications in nanoscale electronics (Cui & Lieber, 2001), optoelectronics (Duan et al., 2001), photonics (Gudiksen et al., 2002; Huang et al., 2001), sensors (Cui et al., 2001), and solar cells (Law et al., 2005) due to their unique electrical, chemical, and optical properties (Li et al., 2006; Thelander et al., 2006; Wang et al., 2008). Nanowires are useful in chemical or biological sensors for detecting single molecules because they have a high surfaceto-volume ratio and a highly sensitive 1D nanostructure that gives rise to large conductivity change associated with binding molecules (Cui et al., 2001; Ramanathan et al., 2005). Conducting polymers, such as polypyrrole, polyaniline, polythiophene, and their derivatives, are promising materials for synthesis of nanostructured materials and devices (Langea et al., 2008; Malinauskas et al., 2005). Compared with other materials, conducting polymers have some unique electrical, chemical, and optical properties because of their conjugated structures, and they are easily synthesized using chemical or electrochemical synthetic methods at room temperatures with low cost (Aleshin, 2006; Briseno et al., 2008; Guimard et al., 2007; Xia et al., 2010). Conducting polymers have electrical and optical properties similar to those of metals and semiconductors, while maintaining the flexibility and properties commonly associated with conventional polymer substances (Dai et al., 2002; Heeger, 2002; Shirakawa, 2002). For example, the electrical conductivity of these polymers can be adjusted from an insulator to traditional metals by varying the species and concentrations of doping ions. Undoped conducting polymers with conductivities of 10-10 to 10-5 S cm-1 can be changed into semiconducting or metallic materials with conductivities of 1 to 104 S cm-1 through a chemical or electrochemical doping process (MacDiarmid, 2002). Also, optical absorption bands and mechanical volume of conducting polymers can be changed by entrapped doping ions. Therefore, they have been used for various applications such as electronic devices (Hashizume, 2006), optoelectronic devices (Noy et al., 2002), actuators (Berdichevsky & Lo, 2006), transistors (Alam et al., 2005), and chemical sensors (Bangar et al., 2009; Garcia-Aljaro et al., 2010). In recent years, 1D conducting polymer nanostructures have been demonstrated to have improved performance with low dimensionality. Many different fabrication methods have