Myoung-Seon Gong

Size-dependent cellular toxicity of silver nanoparticles†

Silver nanoparticles (AgNPs) have found a variety of uses including biomedical materials; however, studies of the cytotoxicity of AgNPs by size effects are only in the beginning stage. In this study, we examined the size-dependent cellular toxicity of AgNPs using three different characteristic sizes (∼ 10, 50, and 100 nm) against several cell lines including MC3T3-E1 and PC12. The cytotoxic effect determined based on the cell viability, intracellular reactive oxygen species generation, lactate dehydrogenase release, ultrastructural changes in cell morphology, and upregulation of stress-related genes (ho-1 and MMP-3) was fairly size- and dose-dependent. In particular, AgNPs stimulated apoptosis in the MC3T3-E1 cells, but induced necrotic cell death in the PC12 cells. Furthermore, the smallest sized AgNPs (10 nm size) had a greater ability to induce apoptosis in the MC3T3-E1 cells than the other sized AgNPs (50 and 100 nm). These data suggest that the AgNPs-induced cytotoxic effects against tissue cells are particle size-dependent, and thus, the particle size needs careful consideration in the design of the nanoparticles for biomedical uses.

Humidity sensor using epoxy resin containing quaternary ammonium salts

Humidity-sensitive epoxy monomer, glycidyl trimethyl ammonium chloride (GTMAC) was selected as the humidity-sensing resin. Polypropylene glycol diglycidyl ether (PPGDGE) and methyl tetrahydrophthalic anhydride (MTPHA) were used as a comonomer and a curing agent, respectively. The humidity-sensitive membranes were composed of GTMAC, PPGDGE and MTPHA. When impedance characteristics of the epoxy resins containing quaternary ammonium salts were measured, the impedance decreased linearly with an increase in the content of GTMAC in its semi-logarithmic graph. The impedance changed from 10 7 to 10 3 O between 30 and 90%RH, which was required for a common humidity sensor. Temperature dependence, frequency dependence and response time were also measured. The humidity-sensitive characteristics of the sensor did not change even after soaking in water. # 2001 Elsevier Science B.V. All rights reserved.

Highly efficient blue OLED based on 9-anthracene-spirobenzofluorene derivatives as host materials

A novel spiro[benzo[c]fluorene-7,9′-fluorene](SBFF)-based blue host material, 9-(10-phenylanthracene-9-yl)SBFF (BH-9PA), 9-(10-(naphthalene-1-yl)anthracene-9-yl)SBFF (BH-9NA) and 9-(10-(4-(naphthalene-1-yl)phenyl)anthracene-9-yl)SBFF (BH-9NPA) were successfully prepared by reacting 9-bromo-SBFF (2) with 10-phenylanthracene-9-yl boronic acid, 10-(naphthalene-1-yl)anthracene-9-yl boronic acid and 10-(4-(naphthalene-1-yl)phenyl)anthracene-9-yl boronic acid through the Suzuki reaction, respectively. Bis[4-(di-p-N,N-diphenylamino)styryl]stilbene (DSA-Ph) and N,N-diphenyl-N′,N′-dim-tolyl-SBFF-5,9-diamine (BD-6MDPA) were used as dopant materials. Blue OLEDs with the configuration ITO/DNTPD/NPB/host : 5% dopant/Alq3/Al-LiF were prepared from the three host materials doped with DSA-Ph and BD-6MDPA dopants and the device composed of BH-9PA doped with DSA-Ph and BD-6MDPA showed blue EL spectra at 468 and 464 nm at 7 V and luminance efficiencies of 7.03 and 6.60 cd A−1, respectively.

Humidity-sensitive properties of a cross-linked polyelectrolyte prepared from mutually reactive copolymers

Two mutually reactive three component copolymers were synthesized to utilize as humidity-sensitive membranes. The major ingredient of a humid membrane is the cross-linked polyelectrolyte obtained from the copolymers 4-vinylpyridine (VP)–(methacryloxyethyl)trimethylammonium chloride (METAC)–n-butyl acrylate (BA) = 1 ∶ 2 ∶ 1, 2 ∶ 2 ∶ 1, 2 ∶ 3 ∶ 1 and 3 ∶ 2 ∶ 1, and 2-chloroethyl acrylate (CEA)–METAC–BA = 1 ∶ 2 ∶ 1, 2 ∶ 2 ∶ 1, 2 ∶ 3 ∶ 1 and 3 ∶ 2 ∶ 1. The humidity sensor prepared from the reaction of VP–METAC–BA = 3 ∶ 2 ∶ 1 with CEA–METAC–BA = 3 ∶ 2 ∶ 1 showed average impedance of 620, 41.9 and 3.38 kΩ at 30, 60 and 90% relative humidity humidity (RH), respectively. Temperature dependence, frequency dependence and response time were measured. The variation of humidity on temperature between 5 and 35 °C was −0.62 to −0.67% RH °C−1 and the hygrometric hysteresis between humidification and desiccation processes were less than ±2% RH. The humidity sensors using polyelectrolyte cross-linked were quite resistant to water.

Humidity sensitive properties of copolymers containing phosphonium salts

Abstract (Vinylbenzyl)triphenylphosphonium chloride (VTPC) was prepared for a humidity-sensitive polyelectrolyte. The humidity-sensitive membranes were composed of cross-linked copolymers with different contents of VTPC, n-butyl acrylate (n-BA) and 2-(N,N-dimethylaminoethyl)methacrylate (VTPC/n-BA/DMAMA=10/35/0, 10/45/0, 10/35/4.5 and 10/35/9). When impedance characteristics of the copolymers were measured, the impedance was decreased with an increase in the content of VTPC. The impedance ranged from 107 Ω to 103 Ω between 50% RH and 95% RH, which was required for a humidity sensor operating at high humidity or a dew point. Temperature dependence, hysteresis and a response time were also measured. The humidity-sensitive characteristics of the cross-linked copolymer of VTPC, n-BA and DAEMA changed little even after soaking in water for 120 min.

Triplet host engineering for triplet exciton management in phosphorescent organic light-emitting diodes

The device performances of green phosphorescent organic light-emitting diodes with a triplet mixed host emitting layer were correlated with the energy levels and composition of the host materials. Two hole-transport-type host materials, (4,4′-N,N′-dicarbazole)biphenyl (CBP) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), were combined with two electron-transport-type host materials, 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) and PH1. The maximum quantum efficiency was obtained in the 5:5 mixed host in the case of TCTA:TPBI and TCTA:PH1, while CBP:PH1 showed the best performances in the 9:1 mixed host. The quantum efficiency of the green mixed host devices was improved by more than 50% compared with that of the corresponding single host devices.

Preparation of silver-coated cotton fabrics using silver carbamate via thermal reduction and their properties.

In this study, cotton fabric was successfully coated with silver to have both antibacterial and conductive properties through a facile thermal reduction process at a low temperature using silver 2-ethylhexylcarbamate as the starting material. The cotton fabric modified with 3-mercaptopropyltriethoxysilane was padded with a solution of silver 2-ethylhexylcarbamate in methanol and then reduced for the in situ generation of Ag nanoparticles by only heating at 130°C. The silver-coated cotton fabrics (cotton/Ag) were examined by a scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. The morphology of cotton/Ag nanocomposite fabrics conveyed a uniform and continuous layer of silver metal on the cotton surface. The results indicated that the silver nanoparticles were assembled on cotton fibers with a size range from 20 to 100 nm. The cotton/Ag imparts high conductivity to the textiles with electric resistance as low as 3.92±0.18 Ω. The antibacterial effects of the treated cotton fabric against Escherichia coli O157:H7 (ATCC 43889) and Staphylococcus aureus (ATCC 25923) were examined and found to be excellent.

Humidity sensitive properties of alkoxysilane-crosslinked polyelectrolyte using sol-gel process

New trialkoxysilyl group-containing copolymers for humidity-sensitive polyelectrolytes were prepared by copolymerization of [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC), 3-(trimethoxysilyl)propyl methacrylate (TSPM) and 2-ethylhexyl acrylate (2-EHA). They were self-crosslinkable copolymers composed of different contents of METAC/TSPM/2-EHA = 4/1/5 and 4/2/4. The resistance varied from 10(7) to 10(3)[capital Omega] between 20% RH and 95% RH, which was required for a humidity sensor operating at ambient humidity. Temperature dependence, hysteresis, response time, water durability and long-term stability at high temperature and humidity were also measured and estimated.

Silk fibroin–polyurethane blends: Physical properties and effect of silk fibroin content on viscoelasticity, biocompatibility and myoblast differentiation

As a way to modify both the physical and biological properties of a highly elastic and degradable polyurethane (PU), silk fibroin (SF) was blended with the PU at differing ratios. With increasing SF content, the tensile strength decreased as did the strain at break; the stiffness increased to around 35 MPa for the highest silk content. C2C12 (a mouse myoblast cell line) cells were used for in vitro experiments and showed significantly improved cell responses with increasing SF content. With increasing SF content the number of non-adherent cells was reduced at both 4 and 8h compared to the sample with the lowest SF content. In addition, muscle marker genes were upregulated compared to the sample containing no SF, and in particular sarcomeric actin and α-actin.

Tetrathiaoxa Macrocycles with Dibenzo-subunits: A Search for New Tl(I)- and Ag(I)-Selective Ionophores

Novel S4O n mixed donor macrocycles (1, n=1; 2, n=2) were synthesized by the coupling reactions of corresponding dichlorides with dithiols under high dilution conditions. Synthesis and crystal structures of Tl+ and Ag+ complexes, [Tl(2)+ and Ag(2)+], with macrocycle 2 are described. The electrode based on macrocycle 2 showed excellent potentiometric sensing ability for Tl+ and Ag+ ions. This remarkable sensing of the proposed electrode can be understood in terms of the synergy effect of a soft–soft acid–base interaction and π-coordination, especially for the Tl+ ion, which was observed from the crystal structure of the corresponding complex.