Moon-Keun Lee

Sonochemical-assisted synthesis of 3D graphene/nanoparticle foams and their application in supercapacitor

Graphene and its derivatives have attracted much attention in application of electrochemical devices. Construction of three-dimensional (3D) heterostructured composites is promising for establishing high-performance devices, which enables large surface area, facilitated ion and electron transport, and synergistic effects between multicomponents. Here, we report a simple and general sonochemical-assisted synthesis to prepare various 3D porous graphene/nanoparticle (i.e., Pt, Au, Pd, Ru, and MnO2) foams using colloidal template. The 3D porous network structure of composite foams significantly improves a large surface area of around 550m(2)g(-1) compared to the bare graphene (215m(2)g(-1)). This unique structure of 3D graphene/MnO2 enables further improvement of electrochemical characteristics, compared with bare graphene/MnO2 composite, showing a high specific capacitance of 421Fg(-1) at 0.1Ag(-1), high rate capability (97% retention at 20Ag(-1)), and good cycling performance (97% retention over 1000 cycles). Moreover, electrochemical impedance analysis demonstrates that electron and ion transfer are triggered by 3D porous structure.

Micropillar arrays enabling single microbial cell encapsulation in hydrogels

Single microbial cell encapsulation in hydrogels is an important task to find valuable biological resources for human welfare. The conventional microfluidic designs are mainly targeted only for highly dispersed spherical bioparticles. Advanced structures should be taken into consideration for handling such aggregated and non-spherical microorganisms. Here, to address the challenge, we propose a new type of cylindrical-shaped micropillar array in a microfluidic device for enhancing the dispersion of cell clusters and the isolation of individual cells into individual micro-hydrogels for potential practical applications. The incorporated micropillars act as a sieve for the breaking of Escherichia coli (E. coli) clusters into single cells in a polymer mixture. Furthermore, the combination of hydrodynamic forces and a flow-focusing technique will improve the probability of encapsulation of a single cell into each hydrogel with a broad range of cell concentrations. This proposed strategy and device would be a useful platform for genetically modified microorganisms for practical applications.

Microbial inactivation and pesticide removal by remote exposure of atmospheric air plasma in confined environments.

Microbial inactivation and pesticide removal by remote exposure of atmospheric air plasma were investigated in confined environments, including an airtight box and commercial refrigerator. The relative sterilization ratios of remote plasma exposure in an airtight box were found to be affected by the distance from the plasma generator, the volume of box and the time of irradiation; however, over 99% saturation was obtained within only 120 s in all experiments. The sterilization of microorganisms and the removal of pesticide in a refrigerator with a volume of 292 l were also successfully achieved, resulting in over 99% inactivation or decontamination in a few minutes. Considering the reported results by direct plasma exposure and circulation, it can be concluded that the confined environment enhances the efficient irradiation of plasma by eliminating air flow. This system can be applied to the storage to keep agricultural products freshly and exclusion of harmful materials on the products.

Surfactant-Free Synthesis of CaSO4 Nanorod/Nanowire by Electrochemical Deposition

High density and ordered CaSO 4 nanorods and nanowires were prepared on a Au-coated Si substrate by electrochemical deposition in a dimethylformamide solution of calcium chloride and thionyl chloride. This approach represents a synthetic route for a rapid and large-scale preparation of CaSO 4 one-dimensional nanostructures. The lengths and diameters of the nanorods and nanowires were controlled by regulating the concentration of the precursor solution. It is suggested that the morphology of the CaSO 4 nanorods and nanowires strongly depends on both the chloride ion and water concentration. The formation mechanism of CaSO 4 on the substrate and in solution is believed to be the result of electrochemical reactions increasing the concentration of sulfate ions via a reaction with calcium cations. During the growth process of CaS0 4 , the chloride ion was adsorbed to a specific side of the CaS0 4 nanostructures such that nanorods and nanowires were grown in one direction.

Bio‐inspired Hierarchical Nanowebs for Green Catalysis

Bio-inspired 3D hierarchical nanowebs are fabricated using silicon micropillars, carbon nanotubes (CNT), and manganese oxide. The Si pillars act as artificial branches for growing CNTs and the secondary metal coating strengthens the structures. The simple but effective structure provides both chemical and mechanical stability to be used as a green catalyst for recycling waste polymers into raw materials.

Development of Lateral Flow Assay Based on Size-Controlled Gold Nanoparticles for Detection of Hepatitis B Surface Antigen

In this study, we developed lateral flow assay (LFA) biosensors for the detection of hepatitis B surface antigens using well-controlled gold nanoparticles (AuNPs). To enhance colorimetric signals, a seeded growth method was used for the preparation of size-controlled AuNPs with a narrow size distribution. Different sizes of AuNPs in the range of 342–137.8 nm were conjugated with antibodies and then optimized for the efficient detection of LFA biosensors. The conjugation stability was investigated by UV-vis spectroscopy of AuNP dispersion at various pH values and concentrations of antibody. Based on optimized conjugation conditions, the use of 42.7 ± 0.8 nm AuNPs exhibited superior performance for the detection of LFAs relative to other sizes of AuNPs.

An integrated and wearable healthcare-on-a-patch for wireless monitoring system

The measurement system for healthcare signals such as heart rate and body temperature is significantly important to prevent and monitor of potential heart attack. Although numerous researchers have developed wearable devices and systems, there are still lots of issues to be solved to expand their applications. To overcome such issues, we propose the new types of healthcare-on-a-patch using flexible PCB and flexible battery. This patch system could measure and transmit the physiological signal on body skin. The heart rate and the body temperature were excellently monitored in Bluetooth wireless communication. Furthermore, it was flexible enough to be rolled in a small barrel while working.

A Universal Spring-Probe System for Reliable Probing of Electrochemical Lab-on-a-Chip Devices

For achieve sensitivity in lab-on-a-chip electrochemical detection, more reliable probing methods are required, especially for repeated measurements. Spring-probes are a promising candidate method which can replace needle-like probes and alligator clips that usually produce scratches on the surface of gold electrodes due to the strong physical contacts needed for electrochemical measurements. The superior reliability of amperometric measurements by a spring-probe system was compared with results by conventional probing methods. We demonstrated that a universal spring-probe system would be potentially suitable to achieve high performance in lab-on-a-chip devices using electrochemical detection.