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Biomedical subjects

Daoben Zhu

Publications and source records attributed to Daoben Zhu.

At least 55 records · Page 3Linked to original sources
PubMed2005

Fabrication of polydiacetylene nanowires by associated self-polymerization and self-assembly processes for efficient field emission properties.

The paper described here concerns a challenge of general interest for producing a novel structure of a polymer aggregate, the achievement of nanowires with controlled diameters. We provide a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes. The polymer nanowire film shows excellent field emission properties with the turn-on field of 8.2 V/mum at 10 muA/cm2 and the maximum current density of 5 mA/cm2 at an applied field of 15 V/mum.

Acetylene↗
PubMed2005

Fluorescent amplifying recognition for DNA G-quadruplex folding with a cationic conjugated polymer: a platform for homogeneous potassium detection.

Single-stranded DNA with G-rich sequences can fold into secondary structures, G-quadruplexes, via intramolecular hydrogen-bonding interactions. This conformational change can be detected by a homogeneous assay method based on fluorescence resonance energy transfer (FRET) from a water-soluble cationic conjugated polymer (CCP) to a fluorescein chromophore labeled at the terminus of the G-quadruplex DNA. The space charge density around the DNA controls the efficiency of FRET from the CCP to the fluorescein. The higher FRET efficiency for the CCP/G-quadruplex pair is correlated to the stronger electrostatic interactions between the more condensed G-quadruplex and the CCP in comparison to the CCP/ssDNA pair. Since the potassium ion can specifically bind to the G-quadruplex DNA, the G-quartet-DNA/CCPs assembly can also be used as a platform to sense the potassium ion in water with high selectivity and sensitivity.

Biosensing Techniques↗
PubMed2005

Actuator based on MWNT/PVA hydrogels.

The first actuator based on multiwalled carbon nanotube (MWNT) hydrogels was developed through simple hydrogelation with poly(vinyl alcohol) (PVA). This actuator exhibited excellent actuating properties compared with the corresponding actuator based on poly(acrylic acid)/PVA hydrogels.

Letter↗
PubMed2005

Tuning the CD spectrum and optical rotation value of a new binaphthalene molecule with two spiropyran units: mimicking the function of a molecular "AND" logic gate and a new chiral molecular switch.

With the view to developing new chiral molecular switches and logic gates, a new binaphthalene molecule with two spiropyran units (1) was synthesized and characterized. Absorption and 1H NMR spectral studies of 1 after reaction with acid/base indicate acidichromism can occur to compound 1. The synergistic actions of acid and UV light irradiation result in a remarkable change for the CD spectrum of the relatively dilute solution of 1, mimicking the behavior of a chiral "AND" gate, since the "ouput" is the CD signal. Furthermore, the optical rotation value of the relatively concentrated solution of 1 can be reversibly tuned after sequential reactions with acid and base, and thus a chiral molecular switch with nondestructive "output" signal is realized. The present results not only add a new example of chiral molecular switch with nondestructive readout but also provide a chiral "AND" gate based on the axial chiral binaphthalene to which switchable units are linked.

Journal Article↗
PubMed2005

Facile route to synthesize multiwalled carbon nanotube/zinc sulfide heterostructures: optical and electrical properties.

A simple method to decorate the multiwalled carbon nanotubes (MWCNTs) with ZnS nanospheres has been developed. The method involves ultrasonic pretreatment and heat treatments of MWCNTs, zinc chloride, and thiourea in ethanol. The heterostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Comparative experiments show that both ultrasonic treatment and heat treatment are necessary for synthesizing the MWCNTs/ZnS heterostructures. Moreover, a photoluminescence spectrum shows that the MWCNTs/ZnS heterostructures feature a broad blue emission at about 430 nm, indicating that there exists significant ground-state interaction between ZnS nanospheres and MWCNTs. Meanwhile, the current-voltage characteristic of the MWCNTs/ZnS exhibits clear rectifying behavior, revealing charge transfer between MWCNTs and ZnS nanospheres.

Journal Article↗
PubMed2005

n-Type field-effect transistors made of an individual nitrogen-doped multiwalled carbon nanotube.

We report on the fabrication and characterization of field-effect transistor based on an individual multiwalled nitrogen-doped carbon nanotube. Our measurements show that the N-doped carbon nanotubes have n-type properties. The contact properties of the tube and Pt electrodes are also studied in detail. Temperature dependence of two-terminal transport experiments suggests that transport is dominated by thermionic emission and tunneling through a 0.2 eV Schottky contact barrier.

Journal Article↗
PubMed2005

High-performance field-effect transistors based on Langmuir-Blodgett films of cyclo[8]pyrrole.

We demonstrate the field-effect transistors (FETs) made of cyclo[8]pyrrole thin films prepared by the Langmuir-Blodgett (LB) method. The cyclo[8]pyrrole molecule possesses a 30-pi-electron system and narrower highest-occupied molecular orbital-lowest-unoccupied molecular orbital energy gap (0.63 eV), forms a stable, reproducible monolayer at the air-water interface, and transfers onto a substrate with a nearly unity transfer ratio and face-to-face configuration due to its strong pi-pi interaction. The LB films are uniform characterized by atomic force microscopy and in ordered form confirmed by X-ray diffraction. The FET exhibited high performances with one of the highest hole mobilities (0.68 cm2 V(-1) s(-1)) for thin-film transistors and a high on/off ratio, implying a promising material in the FET family.

Journal Article↗
PubMed2005

Novel electroactive and photoactive molecular materials based on conjugated donor-acceptor structures for optoelectronic device applications.

Four donor-acceptor functionalized molecular materials with symmetrical structures have been synthesized and investigated for their use in optoelectronic applications. These pi-conjugated molecules consist of one electron-donating moiety, for instance, carbazole, triphenylamine, or phenothiazine at the center, and two acceptors at each side. Introduction of different donor moieties decreases the band gaps allowing a fine-tuning of the optical and electrical properties. These materials exhibit multifunctional properties, such as a red light-emitting behavior and a large photovoltaic effect. Red organic light-emitting diodes were fabricated in a facile nondoping configuration based on these materials. Saturated red-emission is observed with a CIE of x = 0.64 and y = 0.33, and an external quantum efficiency of 0.19%. In addition, our first observation of photovoltaic response in the pi-conjugated molecule with donor-acceptor-donor structure is reported. The organic single-component photovoltaic cells were fabricated and characterized. Their open-circuit voltage and short-circuit current density are 1.1 V and 0.07 mA cm(-2), respectively. The photovoltaic effect corresponds to the absorption characteristics of the compound and depends on the nature of the electron-donating group.

Journal Article↗
PubMed2005

Structures, electronic states, photoluminescence, and carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles.

The excellent electroluminescent (EL) properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles, 1-methyl-1,2,3,4,5-pentaphenylsilole (MPPS), and 1,1,2,3,4,5-hexaphenylsilole (HPS) have been found. Despite some studies devoted to these materials, very little is known about the real origin of their unique EL properties. Therefore, we investigated the structures, photoluminescence (PL), and charge carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles as well as the effect of substituents on these characteristics. The single crystals of the three siloles involving 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS), MPPS, and HPS were grown and their crystal structures were determined by X-ray diffraction. Three siloles have nonplanar molecular structures. The substituents at 1,1-positions enhance the steric hindrance and have predominant influence on the twisted degree of phenyl groups at ring carbons. This nonplanar structure reduces the intermolecular interaction and the likelihood of excimer formation, and increases PL efficiency in the solid state. The silole films show high fluorescence quantum yields (75-85%), whereas their dilute solutions exhibit a faint emission. The electronic structures of the three siloles were investigated using quantum chemical calculations. The highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) are mainly localized on the silole ring and two phenyl groups at 2,5-positions in all cases, while the LUMOs have a significant orbital density at two exocyclic Si-C bonds. The extremely theoretical studies of luminescent properties were carried out. We calculated the nonradiative decay rate of the first excited state as well as the radiative one. It is found that the faint emission of DMTPS in solutions mainly results from the huge nonradiative decay rate. In solid states, molecular packing can remarkably restrict the intramolecular rotation of the peripheral side phenyl ring, which has a large contribution to the nonradiative transition process. This explains why the 1,1-disubstituted 2,3,4,5-tetraphenylsiloles in the thin films exhibit high fluorescence quantum yields. The charge carrier mobilities of the MPPS and HPS films were measured using a transient EL technique. We obtained a mobility of 2.1 x 10(-)(6) cm(2)/V.s in the MPPS film at an electric field of 1.2 x 10(6) V/cm. This mobility is comparable to that of Alq(3), which is one of the most extensively used electron transport materials in organic light-emitting diodes (LEDs), at the same electric field. The electron mobility of the HPS film is about approximately 1.5 times higher than that of the MPPS film. To the best of our knowledge, this kind of material is one of the most excellent emissive materials that possess both high charge carrier mobility and high PL efficiency in the solid states simultaneously. The excellent EL performances of MPPS and HPS are presumably ascribed to these characteristics.

Journal Article↗
PubMed2005

Third-order nonlinear optical properties of an ultrathin film containing a porphyrin derivative.

An ultrathin nanoscopic multilayer film has been fabricated through the electrostatic layer-by-layer self-assembly of negatively charged 5,10,15,20-tetrakis(3,4,5-trihydroxyphenyl)porphyrin (DHP) and oppositely charged polyethylenimine (PEI). UV-vis spectra showed a continuous and uniform deposition process of PEI and DHP. The film structure was characterized by small-angle X-ray diffraction measurement and AFM images. The nonlinear optical properties of ultrathin film were studied by Z-scan technique with laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited strong nonlinear saturated absorption and a self-defocusing effect. The nonlinear absorption coefficient and refractive index of the self-assembly ultrathin film are -9.7 x 10(-5) m/W and -7.56 x 10(-12) m(2)/W, respectively.

Journal Article↗
PubMed2005

A self-assembled nano optical switch and transistor based on a rigid conjugated polymer, thioacetyl-end-functionalized poly(para-phenylene ethynylene).

A nanometer-scale optical switch and transistor were fabricated with thioacetyl-end-functionalized poly(para-phenylene ethynylene)s and Au nanogap electrodes by self-assembly. With photoirradiation, the switch can be switched on/off quickly with a switching ratio as high as 1000. Moreover, the device works well as a p-type transistor. With an increase in gate bias, strong conductance oscillation was observed in this self-assembled transistor (under low temperature 147 K), which is very likely due to single-electron charging oscillations arising from electron tunneling through the nanometer-scale transistor.

Journal Article↗