Chao-Tsen Chen

Synthesis of Fluorescent Carbohydrate-Protected Au Nanodots for Detection of Concanavalin A and Escherichia coli

This study describes a novel, simple, and convenient method for the preparation of water-soluble biofunctional Au nanodots (Au NDs) for the detection of Concanavalin A (Con A) and Escherichia coli (E. coli). First, 2.9 nm Au nanoparticles (Au NPs) were prepared through reduction of HAuCl(4).3H(2)O with tetrakis(hydroxymethyl)phosphonium chloride (THPC), which acts as both a reducing and capping agent. Addition of 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-SH) onto the surfaces of the as-prepared Au NPs yielded the fluorescent mannose-protected Au nanodots (Man-Au NDs) with the size and quantum yield (QY) of 1.8 (+/-0.3) nm and 8.6%, respectively. This QY is higher than those of the best currently available water-soluble, alkanethiol-protected Au nanoclusters. Our fluorescent Man-Au NDs are easily purified and by multivalent interactions are capable of sensing, under optimal conditions, Con A with high sensitivity (LOD = 75 pM) and remarkable selectivity over other proteins and lectins. To the best of our knowledge, this approach provided the lowest LOD value for Con A when compared to the other nanomaterials-based detecting method. Furthermore, we have also developed a new method for fluorescence detection of E. coli using these water-soluble Man-Au NDs. Incubation with E. coli revealed that the Man-Au NDs bind to the bacteria, yielding brightly fluorescent cell clusters. The relationship between the fluorescence signal and the E. coli concentration was linear from 1.00 x 10(6) to 5.00 x 10(7) cells/mL (R(2) = 0.96), with the LOD of E. coli being 7.20 x 10(5) cells/mL.

A New Strategy for Intracellular Delivery of Enzyme Using Mesoporous Silica Nanoparticles: Superoxide Dismutase

We developed mesoporous silica nanoparticle (MSN) as a multifunctional vehicle for enzyme delivery. Enhanced transmembrane delivery of a superoxide dismutase (SOD) enzyme embedded in MSN was demonstrated. Conjugation of the cell-penetrating peptide derived from the human immunodeficiency virus 1 (HIV) transactivator protein (TAT) to mesoporous silica nanoparticle is shown to be an effective way to enhance transmembrane delivery of nanoparticles for intracellular and molecular therapy. Cu,Zn-superoxide dismutase (SOD) is a key antioxidant enzyme that detoxifies intracellular reactive oxygen species, ROS, thereby protecting cells from oxidative damage. In this study, we fused a human Cu,Zn-SOD gene with TAT in a bacterial expression vector to produce a genetic in-frame His-tagged TAT-SOD fusion protein. The His-tagged TAT-SOD fusion protein was expressed in E. coli using IPTG induction and purified using FMSN-Ni-NTA. The purified TAT-SOD was conjugated to FITC-MSN forming FMSN-TAT-SOD. The effectiveness of FMSN-TAT-SOD as an agent against ROS was investigated, which included the level of ROS and apoptosis after free radicals induction and functional recovery after ROS damage. Confocal microscopy on live unfixed cells and flow cytometry analysis showed characteristic nonendosomal distribution of FMSN-TAT-SOD. Results suggested that FMSN-TAT-SOD may provide a strategy for the therapeutic delivery of antioxidant enzymes that protect cells from ROS damage.

Pregnenolone stabilizes microtubules and promotes zebrafish embryonic cell movement

Embryonic cell movement is essential for morphogenesis and the establishment of body shapes, but little is known about its mechanism. Here we report that pregnenolone, which is produced from cholesterol by the steroidogenic enzyme Cyp11a1 (cholesterol side-chain cleavage enzyme, P450scc), functions in promoting cell migration during epiboly. Epiboly is a process in which embryonic cells spread from the animal pole to cover the underlying yolk. During epiboly, cyp11a1 is expressed in an extra-embryonic yolk syncytial layer. Reducing cyp11a1 expression in zebrafish using antisense morpholino oligonucleotides did not perturb cell fates, but caused epibolic delay. This epibolic defect was partially rescued by the injection of cyp11a1 RNA or the supplementation of pregnenolone. We show that the epibolic delay is accompanied by a decrease in the level of polymerized microtubules, and that pregnenolone can rescue this microtubule defect. Our results indicate that pregnenolone preserves microtubule abundance and promotes cell movement during epiboly.

Gold nanoparticle-based competitive colorimetric assay for detection of protein–protein interactions

A gold nanoparticle-based competitive colorimetric assay uses the ensemble of Concanavalin (ConA) and mannopyranoside-encapsulated gold nanoparticles (Man-GNPs) to identify the binding partners for ConA and the binding constants are determined based on the wavelength shifts.

Comparison of thiophene- and selenophene-bridged donor–acceptor low band-gap copolymers used in bulk-heterojunction organic photovoltaics

We report a detailed comparison of absorption spectroscopy, electrochemistry, DFT calculations, field-effect charge mobility, as well as organic photovoltaic characteristics between thiophene- and selenophene-bridged donor–acceptor low-band-gap copolymers. In these copolymers, a significant reduction of the band-gap energy was observed for selenophene-bridged copolymers by UV-visible absorption spectroscopy and cyclic voltammetry. Field-effect charge mobility studies reveal that the enhanced hole mobility of the selenophene-bridged copolymers hinges on the solubilising alkyl side chain of the copolymers. Both cyclic voltammetry experiments and theoretical calculations showed that the decreased band-gap energy is mainly due to the lowering of the LUMO energy level, and the raising of the HOMO energy level is just a secondary cause. These results are reflected in a significant increase of the short circuit current density (JSC) but a slight decrease of the open circuit voltage (VOC) of their bulk-heterojunction organic photovoltaics (BHJ OPVs), of which the electron donor materials are a selenophene-bridged donor–acceptor copolymer: poly{9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl) benzo[c][1,2,5]-thiadiazole} (pCzSe) or poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-b′]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTSe), or a thiophene-bridged donor–acceptor copolymer: poly{9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pCzS) or poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-b′]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTS); the electron acceptor material is [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Judging from our device data, the potential Se–Se interactions of the selenophene-bridged donor–acceptor copolymers, which is presumably beneficial for the fill factor (FF) of BHJ OPVs, is rather susceptible to the device fabrication conditions.

Acridinium salt-based fluoride and acetate chromofluorescent probes: molecular insights into anion selectivity switching.

A series of acridinium salt-based probes capable of detecting fluoride and acetate anions via a nucleophilic attack at the C9 position of the acridinium moiety is reported. The formation of corresponding acridane displays drastic changes, in both UV-vis absorption and fluorescence emission. The sensing mechanism is a reversible process upon treating either tetrafluoroborate salt or an acid.

Photoassisted Synthesis of Luminescent Mannose–Au Nanodots for the Detection of Thyroglobulin in Serum

We have employed mannose-modified gold nanodots (Man-Au NDs) as a luminescence sensor for the detection of the thyroid-cancer marker thyroglobulin (Tg) in homogeneous solutions. The luminescent Man-Au NDs are prepared through the reaction of 2.9 nm-diameter gold nanoparticles (Au NPs) with 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-RSH) under the irradiation of a light-emitting diode (LED). We have found that the irradiation enhances the quantum yield (approximately 11%), alters the emission wavelength and lifetimes, and shortens the preparation time. A luminescence assay has been developed for Tg based on the competition between Tg and Man-Au NDs for the interaction with the concanavalin A (Con A). Because luminescence quenching of the Man-Au NDs by Con A is inhibited by Tg selectivity, we have obtained a highly sensitive and selective assay for Tg.

High efficiency non-dopant blue organic light-emitting diodes based on anthracene-based fluorophores with molecular design of charge transport and red-shifted emission proof

A new series of 9,10-diphenylanthracene (DPA)-based blue fluorophores have been synthesized and characterized for organic light-emitting diode (OLED) applications. These fluorophores have a bulky substituent, such as triphenylsilane in TPSDPA and mesitylene in TMPDPA, on the C-2 position. The C-2 substituent also includes electron transporting diphenylphosphine oxide in PPODPA and dimesitylene borane in BMTDPA, or hole transporting N-phenylnaphthalen-1-amine in NPADPA. For TMPDPA blue fluorophores, 9,10-diphenyl substituents of the anthracene core are further attached to hole-transporting 9H-carbazole in CBZDPA and electron-transporting 2-phenyl-1,3,4-oxadiazole in OXDDPA. Absorption and emission spectroscopic properties of all DPA-derived fluorophores, either in solution or in the condensed phase, were fully characterized and the HOMO/LUMO energy levels of these fluorophores were determined. The frontier molecular orbitals of the DPA derivatives were analysed by theoretical methods to determine the possible intramolecular charge transfer (ICT) characteristics. Whereas the blue emission is best preserved in TMPDPA, in which the non-conjugated bulky mesitylene group suppresses red-shifted emissions, the ICT is attributed to the deterioration in the emissions of NPADPA and BMTDPA. In the solid state, PPODPA suffered from red-shifted and weakened emissions because of adverse crystallization, which is promoted by the dipolar nature of the diphenylphosphine oxide substituent. Non-dopant OLEDs were fabricated with DPA, TPSDPA, TMPDPA, PPODPA, CBZDPA, and OXDDPA. Except for PPODPA, the electroluminescence efficiency of these DPA derivatives was significantly improved compared with that of the DPA OLEDs. In particular, CBZDPA and OXDDPA OLEDs exhibited the best external quantum efficiency of 4.5% and 4.0% with a true blue colour, with CIEx,y coordinates of (0.17, 0.17) and (0.16, 0.18), respectively. The improved electroluminescence efficiency can be attributed to the molecular charge transport design of CBZDPA and OXDDPA.

Generation and Spectroscopic Profiles of Stable Multiarylaminium Radical Cations Bridged by Fluorenes

A series of arylaminofluorene derivatives (DTFA-1, TTFA-2, TAFB-3, and TAFA-4) were synthesized, and the generation of their corresponding arylaminium cation radicals was readily achieved by Cu(ClO(4))(2) in CH(3)CN. Moreover, the cation radicals were stable at ambient temperature with substantially long life times and exhibited distinct colors. The oxidation mechanism and spectroscopic features of the resulting cation radicals were probed by UV-vis-NIR spectroscopy and electron spin resonance experiments.

En Route to White-Light Generation Utilizing Nanocomposites Composed of Ultrasmall CdSe Nanodots and Excited-State Intramolecular Proton Transfer Dyes

One single material that emits white light is of paramount interest for the development of white light-emitting diodes (WLEDs). Here we report a novel nanocomposite, in which a new type of excited-sate intramolecular proton transfer (ESIPT) molecule, namely 5-(1,2-dithiolan-3-yl)-N-(2-{[4-(3-hydroxy-4-oxo-4H-chromen-2-yl)phenyl](methyl)amino}ethyl)pentanamide (HF-N-LA), is anchored onto the surface of ultrasmall CdSe quantum dots through dithiol functionality. Authentic white light with a CIE coordinate of (0.33, 0.33) could then be generated by confluence of 440 nm emission from CdSe and 570 nm proton-transfer tautomer emission from HF-N-LA. Moreover, linear color tunability could be achieved simply by altering relative amount of the two species, i.e., number of HF-N-LA onto CdSe, in one single nanocomposite, thus opening an innovative route toward applying nanocrystals in the field of WLEDs.