Browsing by Author "Lin, Hsiu-Pen"

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Controlling the electrostatic interaction using a thermal signal to structurally change thermoresponsive nanoparticles
(2019-09-20)
Akimoto, Jun
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Lin, Hsiu-Pen
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Li, Yaw-Kuen
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Ito, Yoshihiro
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應用化學系
The negatively charged thermoresponsive polymers poly(benzyl methacrylate)-b-poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PBzMA-b-PAAc-b-PIPAAm) were prepared by reversible-addition fragmentation chain transfer polymerization. The polymer formed core-shell polymeric micelles possessing a thermoresponsive corona composed of PAAc-b-PIPAAm below the lower critical solution temperature (LCST) of the PIPAAm chain. The nonionic thermoresponsive polymeric micelle composed of PBzMA-b-PIPAAm exhibited extensive intermicellar aggregation after the hydrophobic phase transition of the corona-forming PIPAAm chains. In contrast, insertion of the PAAc chain into the thermoresponsive micelle maintained its dispersibility above the LCST of PIPAAm because of the electrostatic repulsion between the micelles. The micelles with short PAAc chains suppressed the effect of the negative charge derived from PAAc below the LCST because of the extended PIPAAm chain on the micellar surface. In contrast, the negative charge property appeared due to collapse of the PIPAAm layer above the LCST. This thermoresponsive change in its electrostatic behavior enables the micelle to control the adsorption and desorption of oppositely charged molecules in response to the temperature change across the LCST.
Magnetic Fe@FeOx, Fe@C and alpha-Fe2O3 Single-Crystal Nanoblends Synthesized by Femtosecond Laser Ablation of Fe in Acetone
(2018-08-01)
Zhang, Dongshi
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Choi, Wonsuk
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Oshima, Yugo
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Wiedwald, Ulf
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Cho, Sung-Hak
There are few reports on zero-field-cooled (ZFC) magnetization measurements for Fe@FeOx or FeOx particles synthesized by laser ablation in liquids (LAL) of Fe, and the minimum blocking temperature (T-B) of 120 K reported so far is still much higher than those of their counterparts synthesized by chemical methods. In this work, the minimum blocking temperature was lowered to 52 K for 4-5 nm alpha-Fe2O3 particles synthesized by femtosecond laser ablation of Fe in acetone. The effective magnetic anisotropy energy density (K-eff) is calculated to be 2.7-5.4 x 10(5) J/m(3), further extending the K-eff values for smaller hematite particles synthesized by different methods. Large amorphous-Fe@alpha-Fe2O3 and amorphous-Fe@C particles of 10-100 nm in diameter display a soft magnetic behavior with saturation magnetization (M-s) and coercivities (H-c) values of 72.5 emu/g and 160 Oe at 5 K and 61.9 emu/g and 70 Oe at 300 K, respectively, which mainly stem from the magnetism of amorphous Fe cores. Generally, the nanoparticles obtained by LAL are either amorphous or polycrystalline, seldom in a single-crystalline state. This work also demonstrates the possibility of synthesizing single-crystalline alpha-Fe2O3 hematite crystals of several nanometers with (104), (113), (116) or (214) crystallographic orientations, which were produced simultaneously with other products including carbon encapsulated amorphous Fe (a-Fe@C) and Fe@FeOx core-shell particles by LAL in one step. Finally, the formation mechanisms for these nanomaterials are proposed and the key factors in series events of LAL are discussed.
Selective Control of Cell Activity with Hydrophilic Polymer-Covered Cationic Nanoparticles
(1970-01-01)
Lin, Hsiu-Pen
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Akimoto, Jun
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Li, Yaw-Kuen
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Ito, Yoshihiro
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交大名義發表
Cationic polymers exhibit high cytotoxicity via strong interaction with cell membranes. To reduce cell membrane damage, a hydrophilic polymer is introduced to the cationic nanoparticle surface. The hydrophilic polymer coating of cationic nanoparticles resulted in a nearly neutral nanoparticle. These particles are applied to mouse fibroblast (3T3) and human cervical adenocarcinoma (Hela) cells. Interestingly, nanoparticles with a long cationic segment decrease cell activity regardless of cell type, while those with a short segment only affect 3T3 cell activity at lower concentrations less than 500 mu g mL(-1). Most nanoparticles are located inside 3T3 cells but on the cell membrane of Hela cells. The short cationic nanoparticle shows negligible cell membrane damage despite its high accumulation on Hela cell membranes. Cell activity changed by hydrophilic polymer-coated cationic nanoparticles is caused by incorporated nanoparticle accumulation in the cells, not cell membrane damage. To suppress the cytotoxicity from the cationic polymer, cationic nanoparticle needs to completely cover with hydrophilic polymer so as not to exhibit the cationic effect and applies to cell with low concentrations to reduce the nonselective cytotoxicity from the cationic polymer.
Step-by-Step Assembled Enzyme-Polymer-Carbon Nanotubes for Solution-Processed Bioreactive Composites
(2019-07-01)
Lin, Hsiu-Pen
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Akimoto, Jun
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Li, Yaw-Kuen
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Ito, Yoshihiro
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Kawamoto, Masuki
Protein-conjugated single-walled carbon nano tubes (SWCNTs) have received much attention for their diverse applications in molecular biology. Intrinsically water insoluble SWCNTs avoid conjugation with proteins, which leads to limited availability of biomolecule nanocarbon composites. Because protein functions are directly affected by assembled structures, the synthesis of heterogeneous composites with bioreactive responses is a great challenge. We demonstrate that step-by-step assembled enzyme/polymer/SWCNTs are obtained by using noncovalent-bonding methodologies in aqueous media. A multifunctional polymer containing aromatic, cationic, and redox-active units allows for a direct aqueous dispersion of SWCNTs through pi interactions and a subsequent charge attraction to the enzyme, which yields the ternary composites. The resulting composites show bioreactive responses in enzyme-conjugated SWCNT networks. The solution-processed glucose oxidase (GO(x))/polymer/SWCNT composite displays a high current density of 1420 mu A cm(-2) by enzymatic oxidation of glucose. Only 2.4 mu g of GO(x) is shown to be necessary for the enzymatic reaction with a sensitivity of 72 mu A mM(-1) cm(-2). This high sensitivity results from the assembled structure through noncovalent-bonding interactions. We demonstrate that the bioreactive composite allows energy conversion from a glucose-including beverage (cola) to electricity. Lactate oxidase-driven bioreactivity also takes place on the structurally organized composite. This step-by-step methodology would be beneficial for enzyme-assisted energy conversion nanocomposites.
Two Birds with One Stone: Spontaneous Size Separation and Growth Inhibition of Femtosecond Laser-Generated Surfactant-Free Metallic Nanoparticles via ex Situ SU-8 Functionalization
(2018-09-01)
Zhang, Dongshi
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Choi, Wonsuk
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Yazawa, Kenjiro
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Numata, Keiji
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Tateishi, Ayaka
Laser ablation in liquids (LAL) offers a facile technique to develop a large variety of surfactant-free nanomaterials with high purity. However, due to the difficulty in the control of the particle synthesis process, the as-prepared nanomaterials always have a broad size distribution with a large polydispersity (s). Surfactant-free properties can also cause problems with particle growth, which further increases the difficulty in size control of the colloids. Therefore, searching for strategies to simultaneously unify the sizes of colloids and inhibit particle growth has become significantly important for LAL-synthesized nanomaterials to be extensively used for biological, catalytic, and optical applications, in which fields particle size plays an important role. In this work, we present a facile way to simultaneously realize these two goals by ex situ SU-8 photoresist functionalization. Ag nanoparticles (NPs) synthesized by femtosecond laser ablation of silver in acetone at laser powers of 300 and 600 mW were used as starting materials. The synthesized Ag NPs have a broad size distribution between 1 and 200 nm with an average size of ca. 5.9 nm and sigma of 127-207%. After ex situ SU-8 functionalization and 6 months storage, most particles larger than 10 nm become aggregates and precipitate, which makes the size distribution narrow with an average diameter of 4-5 nm and s of 48-78%. The precipitation process is accompanied by the decrease in colloid mass from the initial similar to 0.2 to 0.10-0.11 mg after ex situ SU-8 functionalization and 6 months colloid storage. Morphology analysis indicates that ex situ SU-8 functionalization inhibits the particle growth into polygonal nanocrystals. Radical polymerization of SU-8 on Ag NPs is considered to be the reason for both spontaneous size separation and growth inhibition phenomena. Benefiting from Ag NPs embedment and acetone dissolution, the glass-transition temperature of SU-8 photoresist increased from 314 to 331 degrees C according to thermogravimetric analysis. The universality of ex situ SU-8 functionalization-induced growth inhibition and size separation behaviors is further proved using the Au colloids generated by LAL in acetone. This work is expected to provide a new route for better size control of LAL-synthesized colloids via ex situ photoresist functionalization, although a half of colloidal mass is wasted due to radical polymerization-induced colloidal precipitation.