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Yongkeun Oh,Dae-Sung Kwon,Youngkee Eun,Wondo Kim,Min-Ook Kim,Hee-Jin Ko,Seong Gu Kang,Jongbaeg Kim 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.4
In this paper, we present a flexible hybrid energy harvester for single- or multi-source energy collection. To increase harvesting power, piezoelectric and thermoelectric conversions are used simultaneously. The piezoelectric portion of the harvester collects energy from low-frequency kinetic motion using frequency up-conversion. The thermoelectric part is suitable for harvesting energy from a curved surface, thanks to its flexibility. By harvesting from two different energy sources (kinetic and thermal), the harvester allows for sustainable energy harvesting. The average power density obtained was 28.57 and 0.64 μW/cm2 by piezoelectric and thermoelectric conversion, respectively.
Kim, Doyeon,Oh, Nuri,Kim, Kyoohyun,Lee, SangYun,Pack, Chan-Gi,Park, Ji-Ho,Park, YongKeun Elsevier 2018 Methods Vol.136 No.-
<P><B>Abstract</B></P> <P>Delivery of gold nanoparticles (GNPs) into live cells has high potentials, ranging from molecular-specific imaging, photodiagnostics, to photothermal therapy. However, studying the long-term dynamics of cells with GNPs using conventional fluorescence techniques suffers from phototoxicity and photobleaching. Here, we present a method for 3-D imaging of GNPs inside live cells exploiting refractive index (RI) as imaging contrast. Employing optical diffraction tomography, 3-D RI tomograms of live cells with GNPs are precisely measured for an extended period with sub-micrometer resolution. The locations and contents of GNPs in live cells are precisely addressed and quantified due to their distinctly high RI values, which was validated by confocal fluorescence imaging of fluorescent dye conjugated GNPs. In addition, we perform quantitative imaging analysis including the segmentations of GNPs in the cytosol, the volume distributions of aggregated GNPs, and the temporal evolution of GNPs contents in HeLa and 4T1 cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Label-free imaging of gold nanoparticles inside live cells without using fluorescent probes. </LI> <LI> Time-lapsed 3D refractive index imaging with the tomogram over a long period. </LI> <LI> Cross-validation of 3D refractive index tomography of gold nanoparticles inside cells with confocal fluorescent images. </LI> <LI> Quantitative analysis of the volumes and 3D distributions of gold nanoparticles. </LI> </UL> </P>
So Young CHOI,Jeonghun OH,JaeHwang JUNG,YongKeun PARK,Sang Yup LEE 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Polyhydroxyalkanoates (PHAs) are natural polymers accumulated as insoluble granules in numerous microorganisms and are considered sustainable and eco-friendly plastics. Despite great advances in PHA research, spatiotemporal characteristics of PHA granules in vivo are not well understood due to technical limitations. Here we report the results of 3D quantitative analysis of PHA granules in a living cell by measuring the refractive index distributions using optical diffraction tomography. The formation of PHA granules in the cells of Cupriavidus necator, the most-studied native PHA producer, and recombinant Escherichia coli was comparatively examined. Through the statistical analysis of cells, the distinctive differences for PHA granules in the two microorganisms were found, providing insights into PHA biosynthesis mechanism.
So Young CHOI,Jeonghun OH,JaeHwang JUNG,YongKeun PARK,Sang Yup LEE 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
As plastic pollution has been emerging as a serious environmental problem, polyhydroxyalkanoates (PHAs) have been attracting much attention. PHAs are biodegradable natural polymers accumulated in the form of insoluble granules within numerous microorganisms and can be used for various applications such as disposable products, packaging, and medical uses. Despite great advances in PHA research, spatiotemporal characteristics of PHA granule formation in a live bacterial cell are not well understood due to technical limitations. Here, we observed and quantitatively analyzed how PHA granule is being accumulated in living bacteria cells through 3D holographic microscopy. A deeper understanding of PHA granule formation in vivo is now possible, which will help develop efficient microbial plastic factories.