Ansoon Kim

SERS-based pesticide detection by using nanofinger sensors.

Simple, sensitive, and rapid detection of trace levels of extensively used and highly toxic pesticides are in urgent demand for public health. Surface-enhanced Raman scattering (SERS)-based sensor was designed to achieve ultrasensitive and simple pesticide sensing. We developed a portable sensor system composed of high performance and reliable gold nanofinger sensor strips and a custom-built portable Raman spectrometer. Compared to the general procedure and previously reported studies that are limited to laboratory settings, our analytical method is simple, sensitive, rapid, and cost-effective. Based on the SERS results, the chemical interaction of two pesticides, chlorpyrifos (CPF) and thiabendazole (TBZ), with gold nanofingers was studied to determine a fingerprint for each pesticide. The portable SERS-sensor system was successfully demonstrated to detect CPF and TBZ pesticides within 15 min with a detection limit of 35 ppt in drinking water and 7 ppb on apple skin, respectively.

Deterministic nanoparticle assemblies: from substrate to solution

The deterministic assembly of metallic nanoparticles is an exciting field with many potential benefits. Many promising techniques have been developed, but challenges remain, particularly for the assembly of larger nanoparticles which often have more interesting plasmonic properties. Here we present a scalable process combining the strengths of top down and bottom up fabrication to generate deterministic 2D assemblies of metallic nanoparticles and demonstrate their stable transfer to solution. Scanning electron and high-resolution transmission electron microscopy studies of these assemblies suggested the formation of nanobridges between touching nanoparticles that hold them together so as to maintain the integrity of the assembly throughout the transfer process. The application of these nanoparticle assemblies as solution-based surface-enhanced Raman scattering (SERS) materials is demonstrated by trapping analyte molecules in the nanoparticle gaps during assembly, yielding uniformly high enhancement factors at all stages of the fabrication process.

Self-Heating-Induced Deterioration of Electromechanical Performance in Polymer-Supported Metal Films for Flexible Electronics

The retention of electrical performance under the combined conditions of mechanical strain and an electrical current is essential for flexible electronics. Here, we report that even below the critical current density required for electromigration, the electrical current can significantly deteriorate the electromechanical performance of metal film/polymer substrate systems. This leads to a loss of stretchability, and this effect becomes more severe with increasing strain as well as increasing current. The local increase of electrical resistance in the metal film caused by damage, such as localized deformations, cracks, etc., locally raises the temperature of the test sample via Joule heating. This weakens the deformation resistance of the polymer substrate, accelerating the necking instability, and consequently leading to a rapid loss of electrical conductivity with strain. To minimize such a current-induced deterioration of the polymer-supported metal films, we develop and demonstrate the feasibility of two methods that enhance the deformation resistance of the polymer substrate at elevated temperatures: increasing the thickness of the polymer substrate, and utilizing a polymer substrate with a high glass transition temperature.

Elasticity-based development of functionally enhanced multicellular 3D liver encapsulated in hybrid hydrogel

Current in vitro liver models provide three-dimensional (3-D) microenvironments in combination with tissue engineering technology and can perform more accurate in vivo mimicry than two-dimensional models. However, a human cell-based, functionally mature liver model is still desired, which would provide an alternative to animal experiments and resolve low-prediction issues on species differences. Here, we prepared hybrid hydrogels of varying elasticity and compared them with a normal liver, to develop a more mature liver model that preserves liver properties in vitro. We encapsulated HepaRG cells, either alone or with supporting cells, in a biodegradable hybrid hydrogel. The elastic modulus of the 3D liver dynamically changed during culture due to the combined effects of prolonged degradation of hydrogel and extracellular matrix formation provided by the supporting cells. As a result, when the elastic modulus of the 3D liver model converges close to that of the in vivo liver (≅ 2.3 to 5.9u202fkPa), both phenotypic and functional maturation of the 3D liver were realized, while hepatic gene expression, albumin secretion, cytochrome p450-3A4 activity, and drug metabolism were enhanced. Finally, the 3D liver model was expanded to applications with embryonic stem cell-derived hepatocytes and primary human hepatocytes, and it supported prolonged hepatocyte survival and functionality in long-term culture. Our model represents critical progress in developing a biomimetic liver system to simulate liver tissue remodeling, and provides a versatile platform in drug development and disease modeling, ranging from physiology to pathology.nnnSTATEMENT OF SIGNIFICANCEnWe provide a functionally improved 3D liver model that recapitulates in vivo liver stiffness. We have experimentally addressed the issues of orchestrated effects of mechanical compliance, controlled matrix formation by stromal cells in conjunction with hepatic differentiation, and functional maturation of hepatocytes in a dynamic 3D microenvironment. Our model represents critical progress in developing a biomimetic liver system to simulate liver tissue remodeling, and provides a versatile platform in drug development and disease modeling, ranging from physiology to pathology. Additionally, recent advances in the stem-cell technologies have made the development of 3D organoid possible, and thus, our study also provides further contribution to the development of physiologically relevant stem-cell-based 3D tissues that provide an elasticity-based predefined biomimetic 3D microenvironment.