Tiejin Li

Fabrication of Magnetic Luminescent Nanocomposites by a Layer-by-Layer Self-assembly Approach

Magnetic luminescent nanocomposites were prepared via a layer-by-layer (LbL) assembly approach. The Fe3O4 magnetic nanoparticles of 8.5 nm were used as a template for the deposition of the CdTe quantum dots (QDs)/polyelectrolyte (PE) multilayers. The number of polyelectrolyte multilayers separating the nanoparticle layers and the number of QDs/polyelectrolyte deposition cycles were varied to obtain two kinds of magnetic luminescent nanocomposites, Fe3O4/PEn/CdTe and Fe3O4/(PE3/CdTe)n, respectively. The assembly processes were monitored through microelectrophoresis and UV−vis spectra. The topography and the size of the nanocomposites were studied by transmission electron microscopy. The LbL technique for fabricating magnetic luminescent nanocomposites has some advantages to tune their properties. It was found that the selection of a certain number of the inserted polyelectrolyte interlayers and the CdTe QDs loading on the nanocomposites could optimize the photoluminescence properties of the nanocomposites....

Synthesis of water-soluble ZnS : Mn2+ nanocrystals by using mercaptopropionic acid as stabilizer

The synthesis of water-soluble Mn doped ZnS nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer is described. The coordination of Zn ion with MPA helps efficient doping of Mn and thus makes the process reproducible as compared to the common co-precipitation method. To obtain a high luminescent intensity, post-preparative treatments are performed. It is found that the surface states of the nanocrystals, such as the adsorption of oxygen and the coordination of MPA, play important roles in the enhancement of the luminescent intensity.

Application of impedance spectroscopy for monitoring colloid Au-enhanced antibody immobilization and antibody-antigen reactions.

We used colloidal Au to enhance the amount of antibody immobilized on a gold electrode and ultimately monitored the interaction of antigen-antibody by impedance measurement. Self-assembly of 6 nm (diameter) colloidal Au onto the self-assembled monolayers (SAMs) of 4-aminothiophenol modified gold electrode resulted in an easier attachment of antibody. The redox reactions of [Fe(CN)6](4-)/[Fe(CN)6](3-) on the gold surface were blocked due to the procedures of self-assembly of 4-aminothiophenol and antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.4 with various concentrations of antigen at 37 degrees C for 30 min. The antibody recognition layers and their interactions with various concentrations of antigen could be detected by measurements of the impedance change. The results show that this method has good correlation for detection of Hepatitis B virus surface antigen in the range of 0.5-200 microg/l and a detection limit of about 50 ng/l.

Electrochemical detection of DNA immobilized on gold colloid particles modified self-assembled monolayer electrode with silver nanoparticle label.

The target DNA was immobilized successfully on gold colloid particles associated with a cysteamine monolayer on gold electrode surface. Self-assembly of colloidal Au onto a cysteamine modified gold electrode can enlarge the electrode surface area and enhance greatly the amount of immobilized single stranded DNA (ssDNA). The electron-transfer processes of [Fe(CN)6](4-)/[Fe(CN)6](3-) on the gold surface were blocked due to the procedures of the target DNA immobilization, which was investigated by impedance spectroscopy. Then single stranded target DNA immobilized on the gold electrode hybridized with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution, and the indirect determination of the released solubilized Ag(I) ions by anodic stripping voltammetry (ASV) at a carbon fiber microelectrode. The results show that this method has good correlation for DNA detection in the range of 10-800 pmol/l and allows the detection level as low as 5 pmol/l of the target oligonucleotides.

Oxygen-vacancy-related dielectric relaxations in SrTiO3 at high temperatures

We herein present comparative investigation on the dielectric properties of both ceramic and single crystal SrTiO3 samples in the temperature from room temperature to 1073 K. Two relaxations were observed in both samples. They behave as Debye-like and relaxor-like relaxations in ceramic and single crystal samples, respectively. These relaxations were found to be bulk effect related to oxygen-vacancy. In single crystal sample, the relaxations result from the long-range conduction associated with singly and doubly charged oxygen vacancies. In ceramic sample, the oxygen vacancies are more strongly localized in relation to the crystal. This leads to a new phenomenon of formation and dissociation of oxygen vacancy clusters before the vacancies make contribution to the long-range conduction. The low-temperature relaxation in ceramic sample was determined by the clustering and dissociating processes of the oxygen vacancies. The high-temperature relaxation in ceramic sample was found to share the same mechanism a...

Growth of ultrathin SiO2 on Si by surface irradiation with an O2+Ar electron cyclotron resonance microwave plasma at low temperatures

Ultrathin SiO2 films were grown by Si surface irradiation with an O2+Ar electron cyclotron resonance (ECR) microwave plasma at low temperatures. These films without hydrogen and silicon deposition were easily grown in a few minutes at low temperatures and at relatively low working pressures (1.0–3.9×10−1 Pa). The promoting growth process of an ultrathin oxidized layer (1–9 nm) was analyzed by in situ Fourier transform infrared reflective absorption spectroscopy. By using the sputter erosion technique, the dependence of x-ray photoelectron spectroscopy on the depth profiling of the films was obtained. The compositional deviations of the films from the stoichiometric SiO2 were also discussed in the interface region of Si/SiO2. This study indicated that an O2 ECR microwave plasma was efficient to form controlled ultrathin SiO2 dielectric films. The dependence of the film quality on the working pressure and gas flow rate ratios of the O2 to Ar was discussed.

From Achiral Molecular Components to Chiral Supermolecules and Supercoil Self‐Assembly

The self-assembly in chloroform of a pair of achiral molecular compo- nents, 5-(4-dodecyloxybenzylidene)-(1H,3H)-2,4,6-pyrimidinetrione (1) and 4-ami- no-2,6-didodecylamino-1,3,5-triazine (2) was found to generate a mesoscopic super- coil structure some 10 mm in length and about 300 nm in diameter. The self-assembly process took over 1200 h to reach equilibrium in chloroform at room temperature. In this system of positive cooperativity, chiral supermolecules based on a network of hydrogen bonds are initially generated from 1 and 2. Further assembly of such chiral supermolecules results in the formation of the observed mesoscopic supercoil structure. Owing to the lack of chirality in 1 and 2, both left- and right-handed supercoils are observed.

Application of surface photovoltage technique in photocatalysis studies on modified TiO2 photo-catalysts for photo-reduction of CO2

Surface photovoltage spectrum (SPS) is a useful technique in photocatalysis studies. Here, the relationship between the catalytic activities of modified TiO2, which are composed of Pd/RuO2/TiO2 (A), Pd/TiO2 (B), a-TiO2 (C) and b-TiO2 (D) for photoreduction of CO2 and surface photovoltage (SPV) response was studied by means of this technique. The SPV response increased after surface noble metal (Pd and Ru) depositing and a new SPV response band appeared in the SPS curve of A and B in near IR, which was attributed to the surface state population transition formed by Pd deposition. Corresponding to SPV response, the catalytic activity of photoreduction of CO2 improved after surface noble metal (Pd and Ru) depositing. Moreover, the stronger SPV response is, the higher the catalytic activity of photoreduction of CO2 is. The effect of metal depositing on the behavior of photo-generated carriers in TiO2 semiconductor photocatalysts, as well as the mechanism on photoreduction CO2 of A was discussed.

Surface photovoltage spectra and photoelectrochemical properties of semiconductor-sensitized nanostructured TiO2 electrodes

Three kinds of TiO2 nanostructured thin films and their CdS-sensitized films, consisting of different sizes of TiO2 nanoparticles prepared with different methods, have been investigated. The surface photovoltage spectra (SPS) measurements indicate that the density of surface states on TiO2 is likely dependent upon the details of prepared methods. TiO2 particles prepared from basic sol have more surface states than that prepared from acidic sol. When the TiO2 thin films prepared using the TiO2 sols were sensitized by CdS particles, the SPS responses relative to the surface states on TiO2 from 350 to 800 nm were decreased. The photoelectrochemical properties of nanostructured TiO2 electrodes suggest that the fewer the surface states and the smaller the particle sizes of TiO2, the larger the photocurrent response. For CdS sensitized TiO2 thin film electrode, it is shown that the semiconductor sensitization is an efficient way to decrease the influence of surface states on the charge separation, and can improve the intensity of photocurrent response

A new type of organic-inorganic multilayer: fabrication and photoelectric properties

Abstract Fabrication and photoelectric characteristics of a new type of organic-inorganic alternating multilayer are reported. The multilayers exhibit a strong photovoltaic response in spite of their weak absorbance. Electric field induced surface photovoltage spectroscopy (EFISPS) indicates obvious unilateral selectivity for the application of an external voltage on multilayers