Seyeong Lee

Sub-0.5 V Highly Stable Aqueous Salt Gated Metal Oxide Electronics

Recently, growing interest in implantable bionics and biochemical sensors spurred the research for developing non-conventional electronics with excellent device characteristics at low operation voltages and prolonged device stability under physiological conditions. Herein, we report high-performance aqueous electrolyte-gated thin-film transistors using a sol-gel amorphous metal oxide semiconductor and aqueous electrolyte dielectrics based on small ionic salts. The proper selection of channel material (i.e., indium-gallium-zinc-oxide) and precautious passivation of non-channel areas enabled the development of simple but highly stable metal oxide transistors manifested by low operation voltages within 0.5 V, high transconductance of ~1.0 mS, large current on-off ratios over 107, and fast inverter responses up to several hundred hertz without device degradation even in physiologically-relevant ionic solutions. In conjunction with excellent transistor characteristics, investigation of the electrochemical nature of the metal oxide-electrolyte interface may contribute to the development of a viable bio-electronic platform directly interfacing with biological entities in vivo.

Polypyrrole multilayer-laminated cellulose for large-scale repeatable mercury ion removal

In this research, we report a polypyrrole (PPy) multilayer-laminated cellulose network aimed at the cost-effective removal of aqueous potentially toxic metal ions with high adsorption efficiency and good adsorbent recyclability. The preparation of conformal adsorbent coatings on a fibrous cellulose network was accomplished by performing multiple cycles of simple dip-coating of a non-toxic oxidant and vapor-phase polymerization of PPy. The resultant PPy multilayer-deposited cellulose exhibited stable adhesion between the vapor-deposited PPy and the underlying cellulose support even in a strongly acidic solution. Using this non-hazardous hybrid adsorbent, mercury ions could be efficiently adsorbed over a large pH range with a maximum specific adsorption capacity of 31.689 mg g−1, either in the form of a thick suspended adsorbent for large-scale decontamination or a thin dripper-type membrane for portable water purification. Furthermore, the PPy multilayer-laminated cotton fabric enabled the large-scale repetitive removal of mercury ions (100 ppm, 1 liter) with efficiency above 91%. This study suggests that the PPy-cotton hybrid may serve as a large-scale, economical, and recyclable decontamination platform for efficient removal of highly potentially toxic metal ions (e.g., Hg(II) and Cr(VI)), which could be beneficial for water purification, particularly in resource-limited locations.

Heparin-immobilized gold-assisted controlled release of growth factors via electrochemical modulation

We developed a versatile platform for the electrochemical release of growth factors assisted by a heparin-immobilized gold surface. The controlled release of basic fibroblast growth factor (bFGF) from heparinized gold could be effectively modulated by biphasic electrochemical stimulation which actively controlled specific interactions between heparin and bFGF in a remote manner so that the released bFGF maintained its bioactivity.

Strong contact coupling of neuronal growth cones with height-controlled vertical silicon nanocolumns

In this study, we report that height-controlled vertically etched silicon nano-column arrays (vSNAs) induce strong growth cone-to-substrate coupling and accelerate In vitroneurite development while preserving the essential features of initial neurite formation. Large-scale preparation of vSNAs with flat head morphology enabled the generation of well-controlled topographical stimulation without cellular impalement. A systematic analysis on topography-induced variations on cellular morphology and cytoskeletal dynamics was conducted. In addition, neurite development on the grid-patterned vSNAs exhibited preferential adhesion to the nanostructured region and outgrowth directionality. The arrangement of cytoskeletal proteins and the expression of a focal adhesion complex indicated that a strong coupling existed between the underlying nanocolumns and growth cones. Furthermore, the height-controlled nanocolumn substrates differentially modulated neurite polarization and elongation. Our findings provide an important insight into neuron-nanotopography interactions and their role in cell adhesion and neurite development.

Hydrogen production based on a photoactivated nanowire-forest

For several decades, the key challenge associated with thermochemical hydrogen generation has been the achievement of water splitting and catalyst regeneration at low temperatures while maintaining a reasonably high conversion efficiency over many cycles. Herein, we report low-temperature thermochemical hydrogen generation using hierarchically assembled iron oxide nanoarchitectures. Iron oxide nanoparticles conformally deposited onto a SnO2 nanowire forest allowed the splitting of water molecules and the production of hydrogen gas at temperatures of 400–800 °C, with a high specific gas-forming rate as high as ∼25000 μmol per g per cycle (250 min). More remarkably, deep-ultraviolet photoactivation enabled low-temperature (200 °C) catalyst regeneration and thereby multiple cycles of hydrogen production without any significant coalescence of the oxide nanoparticles nor substantial loss of the water-splitting efficiency. Hierarchically arranged iron oxide nanoarchitectures, in combination with photochemical catalyst regeneration, are promising for practical hydrogen generation by harvesting wasted thermal energy, even at temperatures below 500 °C.

Correction: Polypyrrole multilayer-laminated cellulose for large-scale repeatable mercury ion removal

Correction for ‘Polypyrrole multilayer-laminated cellulose for large-scale repeatable mercury ion removal’ by Zahid Hanif et al., J. Mater. Chem. A, 2016, 4, 12425–12433.

Vertical nanocolumn-assisted pluripotent stem cell colony formation with minimal cell-penetration

The biological applications of vertical nanostructures mostly rely on their intracellular accessibility through the cellular membrane by promoting cell-to-nanostructure interactions. Herein, we report a seemingly counter-intuitive approach for the spontaneous formation of mouse induced pluripotent stem cell (iPSC)-derived three-dimensional spherical colonies with unlimited self-renewal and differentiation potential. The comprehensive analyses of iPSCs cultured on vertical silicon nanocolumn arrays (vSNAs) with various nanocolumn geometries show reduced cell-to-substrate adhesion and enhanced cell-to-cell interactions under optimized vSNA conditions, successfully accommodating the spontaneous production of iPSC-derived spherical colonies. Remarkably, these colonies which were only minimally penetrated by and thereby easily harvested from wafer-sized vSNAs display a substantial increase in pluripotency marker expression and successfully differentiate into three germ layers. Our vSNAs capable of large-scale fabrication, efficient for spherical colony formation, and reusable for multiple iPSC culture could serve as a broad-impact culture platform for stem cell research.