Donguk Kwon

Highly Sensitive, Flexible, and Wearable Pressure Sensor Based on a Giant Piezocapacitive Effect of Three-Dimensional Microporous Elastomeric Dielectric Layer.

We report a flexible and wearable pressure sensor based on the giant piezocapacitive effect of a three-dimensional (3-D) microporous dielectric elastomer, which is capable of highly sensitive and stable pressure sensing over a large tactile pressure range. Due to the presence of micropores within the elastomeric dielectric layer, our piezocapacitive pressure sensor is highly deformable by even very small amounts of pressure, leading to a dramatic increase in its sensitivity. Moreover, the gradual closure of micropores under compression increases the effective dielectric constant, thereby further enhancing the sensitivity of the sensor. The 3-D microporous dielectric layer with serially stacked springs of elastomer bridges can cover a much wider pressure range than those of previously reported micro-/nanostructured sensing materials. We also investigate the applicability of our sensor to wearable pressure-sensing devices as an electronic pressure-sensing skin in robotic fingers as well as a bandage-type pressure-sensing device for pulse monitoring at the human wrist. Finally, we demonstrate a pressure sensor array pad for the recognition of spatially distributed pressure information on a plane. Our sensor, with its excellent pressure-sensing performance, marks the realization of a true tactile pressure sensor presenting highly sensitive responses to the entire tactile pressure range, from ultralow-force detection to high weights generated by human activity.

Soft Nanocomposite Based Multi-point, Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography

The practical utilization of soft nanocomposites as a strain mapping sensor in tactile sensors and artificial skins requires robustness for various contact conditions as well as low-cost fabrication process for large three dimensional surfaces. In this work, we propose a multi-point and multi-directional strain mapping sensor based on multiwall carbon nanotube (MWCNT)-silicone elastomer nanocomposites and anisotropic electrical impedance tomography (aEIT). Based on the anisotropic resistivity of the sensor, aEIT technique can reconstruct anisotropic resistivity distributions using electrodes around the sensor boundary. This strain mapping sensor successfully estimated stretch displacements (error of 0.54 ± 0.53 mm), surface normal forces (error of 0.61 ± 0.62 N), and multi-point contact locations (error of 1.88 ± 0.95 mm in 30 mm × 30 mm area for a planar shaped sensor and error of 4.80 ± 3.05 mm in 40 mm × 110 mm area for a three dimensional contoured sensor). In addition, the direction of lateral stretch was also identified by reconstructing anisotropic distributions of electrical resistivity. Finally, a soft human-machine interface device was demonstrated as a practical application of the developed sensor.

Extremely Robust and Patternable Electrodes for Copy-Paper-Based Electronics.

We propose a fabrication process for extremely robust and easily patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary donor layer and a simple laminating process, AgNWs can be easily transferred to copy paper as well as various other substrates using a dry process. Intercalating a polymeric binder between the AgNWs and the substrate through a simple printing technique enhances adhesion, not only guaranteeing high foldability of the electrodes, but also facilitating selective patterning of the AgNWs. Using the proposed process, extremely crease-tolerant electronics based on copy paper can be fabricated, such as a printed circuit board for a 7-segment display, portable heater, and capacitive touch sensor, demonstrating the applicability of the AgNWs-based electrodes to paper electronics.

Exogenous Gene Integration for Microalgal Cell Transformation Using a Nanowire-Incorporated Microdevice.

Superior green algal cells showing high lipid production and rapid growth rate are considered as an alternative for the next generation green energy resources. To achieve the biomass based energy generation, transformed microalgae with superlative properties should be developed through genetic engineering. Contrary to the normal cells, microalgae have rigid cell walls, so that target gene delivery into cells is challengeable. In this study, we report a ZnO nanowire-incorporated microdevice for a high throughput microalgal transformation. The proposed microdevice was equipped with not only a ZnO nanowire in the microchannel for gene delivery into cells but also a pneumatic polydimethylsiloxane (PDMS) microvalve to modulate the cellular attachment and detachment from the nanowire. As a model, hygromycin B resistance gene cassette (Hyg3) was functionalized on the hydrothermally grown ZnO nanowires through a disulfide bond and released into green algal cells, Chlamydomonas reinhardtii, by reductive cleavage. During Hyg3 gene delivery, a monolithic PDMS membrane was bent down, so that algal cells were pushed down toward ZnO nanowires. The supply of vacuum in the pneumatic line made the PDMS membrane bend up, enabling the gene delivered algal cells to be recovered from the outlet of the microchannel. We successfully confirmed Hyg3 gene integrated in microalgae by amplifying the inserted gene through polymerase chain reaction (PCR) and DNA sequencing. The efficiency of the gene delivery to algal cells using the ZnO nanowire-incorporated microdevice was 6.52 × 10(4)- and 9.66 × 10(4)-fold higher than that of a traditional glass bead beating and electroporation.

Porous dielectric elastomer based ultra-sensitive capacitive pressure sensor and its application to wearable sensing device

In this paper, we report a wearable and flexible capacitive pressure sensor based on porous dielectric elastomer with ultra-high sensitivity and stability. The capacitance response to a wide pressure range of 0~130kPa was investigated, which is generally considered as a human tactile pressure regime. The porous dielectric layer based pressure sensor showed highly sensitive and stable performance with pore-closing mechanism over the whole tactile pressure regime without any drift or structural instability. Finally, we demonstrated a bandage-type wearable pressure sensor for real-time monitoring of human wrist pulse.

Rapid, High-Throughput, and Direct Molecular Beacon Delivery to Human Cancer Cells Using a Nanowire-Incorporated and Pneumatic Pressure-Driven Microdevice

Tracking and monitoring the intracellular behavior of mRNA is of paramount importance for understanding real-time gene expression in cell biology. To detect specific mRNA sequences, molecular beacons (MBs) have been widely employed as sensing probes. Although numerous strategies for MB delivery into the target cells have been reported, many issues such as the cytotoxicity of the carriers, dependence on the random probability of MB transfer, and critical cellular damage still need to be overcome. Herein, we have developed a nanowire-incorporated and pneumatic pressure-driven microdevice for rapid, high-throughput, and direct MB delivery to human breast cancer MCF-7 cells to monitor survivin mRNA expression. The proposed microdevice is composed of three layers: a pump-associated glass manifold layer, a monolithic polydimethylsiloxane (PDMS) membrane, and a ZnO nanowire-patterned microchannel layer. The MB is immobilized on the ZnO nanowires by disulfide bonding, and the glass manifold and PDMS membrane serve as a microvalve, so that the cellular attachment and detachment on the MB-coated nanowire array can be manipulated. The combination of the nanowire-mediated MB delivery and the microvalve function enable the transfer of MB into the cells in a controllable way with high cell viability and to detect survivin mRNA expression quantitatively after docetaxel treatment.

High-Sensitivity and Low-Power Flexible Schottky Hydrogen Sensor Based on Silicon Nanomembrane

High-performance and low-power flexible Schottky diode-based hydrogen sensor was developed. The sensor was fabricated by releasing Si nanomembrane (SiNM) and transferring onto a plastic substrate. After the transfer, palladium (Pd) and aluminum (Al) were selectively deposited as a sensing material and an electrode, respectively. The top-down fabrication process of flexible Pd/SiNM diode H2 sensor is facile compared to other existing bottom-up fabricated flexible gas sensors while showing excellent H2 sensitivity (Δ I/ I0 > 700-0.5% H2 concentrations) and fast response time (τ10-90 = 22 s) at room temperature. In addition, selectivity, humidity, and mechanical tests verify that the sensor has excellent reliability and robustness under various environments. The operating power consumption of the sensor is only in the nanowatt range, which indicates its potential applications in low-power portable and wearable electronics.

Self-powered, highly sensitive pressure sensor based on thin-film solar cell and pressure-responsive porous elastomer film

This paper reports a novel flexible optical pressure sensor based on a porous elastomer film as a light transmission medium with ultra-high sensitivity and simplicity. The pore-closing behavior under external pressure and corresponding change of light transmittance of porous elastomer film were investigated. The porous elastomer film based optical pressure sensor showed highly sensitive and stable performance with the sensitivity of 2.177 kPa−1 over the pressure range of 0–10 kPa. Finally, the optical pressure sensor was integrated with thin film solar cell to modulate the generated electrical current towards self-powered sensing platform.

Molecular Delivery: Rapid, High-Throughput, and Direct Molecular Beacon Delivery to Human Cancer Cells Using a Nanowire-Incorporated and Pneumatic Pressure-Driven Microdevice (Small 46/2015)

A nanowire-incorporated and pneumatic pressure-driven microdevice for rapid, high-throughput and direct molecular beacon (MB) delivery is described by I. Park, T. S. Seo, and co-workers. On page 6215, they show how the microdevice, composed of a manifold layer, a monolithic PDMS membrane, and a nanowire-patterned microchannel layer, could manipulate cellular movement, so the attachment and detachment from the MB-functionalized nanowire array is performed in a controllable way to increase MB delivery efficiency.

A nanowire-integrated microfluidic device for hydrodynamic trapping and anchoring of bacterial cells

In this work, we proposed a novel method for facile hydrodynamic trapping and anchoring of bacterial cells using nanowire array with fishnet-like structure in microfluidic channel. Vertically well-aligned ZnO nanowires were directly synthesized onto side walls of microslit structures by hydrothermal method to form mesh-like cage structures. We found that the mesh-like cages were effective in trapping and anchoring of Escherichia coli cells as model bacteria. In addition, we observed two anchoring modes; impaling and wedging, by electron microscopy and they resulted in irreversible and reversible damage to the anchored cells, respectively. We expected that the suggested bacterial cell trapping method can be used as a simple cell-manipulating platform for advanced microfluidic system.